1. Theme Actual Significance      Anaesthesiology is unique in that it requires a working familiarity with mostother speci...
5.2. Pediatric Anesthetic Risk5.3. Pediatric Anesthetic Techniques (Preoperative Interview, PreoperativeFasting, Premedica...
impaired, resuscitation must be initiated immediately. In critically ill patients,resuscitation and assessment proceed sim...
intubation (blind or fiberoptic) in spontaneously breathing patients with suspectedcervical spine injury, although this te...
bleeding; the second priority is to replace intravascular volume. Cardiac arrestduring transport to the hospital or shortl...
ExposureThe patient should be undressed to allow examination for injuries. In-lineimmobilization should be used if a neck ...
catalogues all injuries after initial resuscitation and operative interventions. Ittypically occurs within 24 h of injurie...
avoid nitrous oxide entirely in these patients because of the possibility of apneumothorax and because it limits inspired ...
passage of an endotracheal tube or nasogastric tube in patients with basal skullfractures risks cribriform plate perforati...
Trauma to the chest may severely compromise the function of the heart orlungs, leading to cardiogenic shock or hypoxia. A ...
spontaneous inspiration), and a high index of suspicion will help make thediagnosis. Pericardiocentesis provides temporary...
intraabdominal injuries do not have pain or signs of peritoneal irritation (muscleguarding, percussion tenderness, or ileu...
hemorrhage. Transfusion-induced hyperkalemia           is   equally   as   lethal   asexsanguination and must be treated a...
compartment pressures: greater than 45 mm Hg or within 10–30 mm Hg ofdiastolic blood pressure. Early fasciotomy to save th...
Anesthesia for Thoracic Surgery       Indications and techniques for thoracic surgery have continually evolvedsince its or...
All these effects worsen ventilation/perfusion mismatching and predispose tohypoxemia.The Open Pneumothorax       The lung...
Factors that decrease blood flow to the ventilated lung can be equallydetrimental; they counteract the effect of HPV by in...
The balance between comfort and respiratory depression in patients withmarginal lung function is difficult to achieve with...
due to necrosis of the suture line associated with inadequate blood flow orinfection.       Some complications are rare bu...
approaches to hip replacement utilizing computer-assisted surgery, arenecessitating modifications in anesthetic management...
replaced, patient, and surgical technique. In many cases cemented and cementlesscomponents are used in the same patient (e...
minute ventilation in the spontaneously breathing patient and, rarely,dysrhythmias. Ironically, cuff deflation and blood r...
precipitant event. Signs during general anesthesia may include a decline in ETCO2and arterial oxygen saturation or a rise ...
guidelines of the American College of Obstetricians and Gynecologists andAmerican Society of Anesthesiologists require tha...
little or no neonatal respiratory depression and are reported to have no effect onApgar scores. Morphine is not used becau...
example, the ED50 during labor is 124 mkg for epidural fentanyl and 21 mkg forepidural sufentanil. The higher doses may be...
abandoned because of less versatility (they are most effective for perinealanalgesia/anesthesia), the need for large volum...
patients is reported to be 5 cm from the skin. Placement of the epidural catheter atthe L3–4 or L4–5 interspace is general...
epidural catheter provides a route for subsequent analgesia for labor and deliveryor anesthesia for cesarean section. Addi...
Version and extractionManual removal of a retained placentaReplacement of an inverted uterusPsychiatric patients who becom...
anesthesia has been associated with higher maternal mortality. Deaths associatedwith general anesthesia are generally rela...
of phenylephrine, 25–100 mkg, or an infusion up to 100 mkg/min may also be usedsafely. Some studies suggest less neonatal ...
Pediatric patients are not small adults. Neonates (0–1 months), infants (1–12months), toddlers (1–3 years), and small chil...
are lower in neonates than in adults, resulting in even faster induction times andpotentially increasing the risk of overd...
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
Bohomolets anaesthesiology clinical
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Bohomolets anaesthesiology clinical

  2. 2. 1. Theme Actual Significance Anaesthesiology is unique in that it requires a working familiarity with mostother specialties, including surgery and its subspecialties, internal medicine,pediatrics, and obstetrics as well as clinical pharmacology, applied physiology, andbiomedical technology. There are a lot of special considerations in different fieldsof Surgery. The purposes of this topic is to familiarize students with features ofanaesthesia in some special fields.2. Educational purposes of practical classThe Core Topics are:1. Anesthesia for the Trauma Patient1.1. Initial Assessment (Primary Survey, Secondary Survey, Tertiary Survey)1.2. Anesthetic Considerations1.2.1. General Considerations1.2.2. Head and Spinal Cord Trauma1.2.3. Chest Trauma1.2.4. Abdominal Trauma1.2.5. Exremity Trauma2. Anesthesia for Thoracic Surgery2.1. Special Consideretions (The Lateral Decubitus Position, Positive-PressureVentilation, Open Pneumothorax, Mediastinal Shift, One-Lung Ventilation)2.2. Postoperative Management2.3. Postoperative Complications3. Anesthesia for Orthopedic Surgery3.1. Special Considerations in Orthopedic Surgery (Bone Cement, PneumaticTourniquets)3.2. Special Complications (Fat Embolism Syndrome, Deep Venous Thrombosisand Thromboembolism)4. Obstetric Anesthesia4.1. Anesthesia for Labor and Vaginal Delivery4.1.1. Psychological and Nonpharmacological Techniques4.1.2. Parenteral Agents4.1.3. Pudendal Nerve Block4.1.4. Regional Anesthetic Techniques (Lumbar Epidural Anaglesia, CombinedSpinal and Epidural (CSE) Analgesia, Spinal Anesthesia)4.1.5. General Anesthesia4.2. Anesthesia for Cesarean Section4.2.1. Regional anesthesia4.2.2. CSE Anesthesia4.2.3. General Anesthesia5. Pediatric Anesthesia5.1. Pharmacological Differences (Inhalational Anesthetics, NonvolatileAnesthetics, Muscle Relaxants)
  3. 3. 5.2. Pediatric Anesthetic Risk5.3. Pediatric Anesthetic Techniques (Preoperative Interview, PreoperativeFasting, Premedication, Monitoring, Intravenous Access, Regional Anesthesia,Sedation for Procedures in and out of the Operating Room)5.4. Emergence and Recovery5.4.1. Laryngospasm5.4.2. Postintubation Croup5.4.3.Postoperative Pain Management6. Geriatric Anesthesia6.1. Age-Related Anatomic and Physiological Changes6.2. Age-Related Pharmacological Changes (Inhalational Anesthetics, NonvolatileAnesthetic Agents, Muscle Relaxants)7. Postanesthesia Care7.1. Emergence from General Anesthesia7.1.1. Delayed Emergence8Routine Recovery: General Anesthesia7.1.2 Routine Recovery: Regional Anesthesia7.2.Pain Control7.3. Nausea and Vomiting7.4. Shivering and Hypothermia7.5. Discharge from ICU or Recovery Room3. Contents of a theme Anesthesia for the Trauma Patient Trauma is the leading cause of death in the world from the first to the thirty-fifth year of age. Up to one-third of all hospital admissions are directly related totrauma. Fifty percent of trauma deaths occur immediately, with another 30%occurring within a few hours of injury (the "golden hour"). Because many traumavictims require immediate surgery, anesthesiologists can directly affect theirsurvival. In fact, the role of the anesthesiologist is often that of primaryresuscitator, with provision of anesthesia a secondary activity. It is important forthe anesthesiologist to remember that these patients may have an increasedlikelihood of being drug abusers, acutely intoxicated, and carriers of hepatitis orhuman immunodeficiency virus (HIV). This chapter presents a framework for theinitial assessment of the trauma victim and anesthetic considerations in thetreatment of patients with injuries of the head and spine, chest, abdomen, andextremities.Initial Assessment The initial assessment of the trauma patient can be divided into primary,secondary, and tertiary surveys. The primary survey should take 2–5 min andconsists of the ABCDE sequence of trauma: Airway, Breathing, Circulation,Disability, and Exposure. If the function of any of the first three systems is
  4. 4. impaired, resuscitation must be initiated immediately. In critically ill patients,resuscitation and assessment proceed simultaneously by a team of traumapractitioners. Basic monitoring including the electroencephalograph (ECG),noninvasive blood pressure, and pulse oximetry can often be initiated in the fieldand is continued during treatment. Trauma resuscitation includes two additionalphases: control of hemorrhage and definitive repair of the injury. Morecomprehensive secondary and tertiary surveys of the patient follow the primarysurvey.Primary SurveyAirway Establishing and maintaining an airway is always the first priority. If apatient can talk the airway is usually clear, but if unconscious the patient willlikely require airway and ventilatory assistance. Important signs of obstructioninclude snoring or gurgling, stridor, and paradoxical chest movements. Thepresence of a foreign body should be considered in unconscious patients.Advanced airway management (such as endotracheal intubation, cricothyrotomy,or tracheostomy) is indicated if there is apnea, persistent obstruction, severe headinjury, maxillofacial trauma, a penetrating neck injury with an expandinghematoma, or major chest injuries. Cervical spine injury is unlikely in alert patients without neck pain ortenderness. Five criteria increase the risk for potential instability of the cervicalspine: (1) neck pain, (2) severe distracting pain, (3) any neurological signs orsymptoms, (4) intoxication, and (5) loss of consciousness at the scene. A cervicalspine fracture must be assumed if any one of these criteria is present, even if thereis no known injury above the level of the clavicle. Even with these criteria, theincidence of cervical spine trauma is approximately 2%. The incidence of cervicalspine instability increases up to 10% in the presence of a severe head injury. Toavoid neck hyperextension, the jaw-thrust maneuver is the preferred means ofestablishing an airway. Oral and nasal airways may help maintain airway patency.Unconscious patients with major trauma are always considered to be at increasedrisk for aspiration, and the airway must be secured as soon as possible with anendotracheal tube or tracheostomy. Neck hyperextension and excessive axialtraction must be avoided, and manual immobilization of the head and neck by anassistant should be used to stabilize the cervical spine during laryngoscopy("manual in-line stabilization" or MILS). The assistant places his or her hands oneither side of the head, holding down the occiput and preventing any head rotation.Studies have demonstrated neck movement, however, particularly at C1 and C2,during mask ventilation and direct laryngoscopy despite attempts at stabilization(eg, MILS, axial traction, sandbags, forehead tape, soft collar, Philadelphia [hard]collar). Of all these techniques, MILS may be most effective, but it also makesdirect laryngoscopy more difficult. For this reason, some clinicians prefer nasal
  5. 5. intubation (blind or fiberoptic) in spontaneously breathing patients with suspectedcervical spine injury, although this technique may be associated with a higher riskof pulmonary aspiration. Others advocate use of a lightwand, Bullardlaryngoscope, WuScope, or an intubating laryngeal mask airway. Clearly, theexpertise and preferences of individual clinicians affect the choice of technique,together with the need for expediency and risks of complications in a given patient.Most practitioners have greater familiarity with oral intubation, and this techniqueshould be considered in patients who are apneic and require immediate intubation.Furthermore, nasal intubation should be avoided in patients with midface or basilarskull fractures. If an esophageal obturator airway has been placed in the field, itshould not be removed until the trachea has been intubated because of thelikelihood of regurgitation. Laryngeal trauma makes a complicated situation worse. Open injuries maybe associated with bleeding from major neck vessels, obstruction from hematomaor edema, subcutaneous emphysema, and cervical spine injuries. Closed laryngealtrauma is less obvious but can present as neck crepitations, hematoma, dysphagia,hemoptysis, or poor phonation. An awake intubation with a small endotrachealtube (6.0 in adults) under direct laryngoscopy or fiberoptic bronchoscopy withtopical anesthesia can be attempted if the larynx can be well visualized. If facial orneck injuries preclude endotracheal intubation, tracheostomy under localanesthesia should be considered. Acute obstruction from upper airway trauma mayrequire emergency cricothyrotomy or percutaneous or surgical tracheostomy.Breathing Assessment of ventilation is best accomplished by the look, listen, and feelapproach. Look for cyanosis, use of accessory muscles, flail chest, and penetratingor sucking chest injuries. Listen for the presence, absence, or diminution of breathsounds. Feel for subcutaneous emphysema, tracheal shift, and broken ribs. Theclinician should have a high index of suspicion for tension pneumothorax andhemothorax (see below), particularly in patients with respiratory distress. Pleuraldrainage may be necessary before the chest X-ray can be obtained. Most critically ill trauma patients require assisted—if not controlled—ventilation. Bag-valve devices (eg, a self-inflating bag with a nonrebreathingvalve) usually provide adequate ventilation immediately after intubation andduring periods of patient transport. A 100% oxygen concentration is delivered untiloxygenation is assessed by arterial blood gases.Circulation Adequacy of circulation is based on pulse rate, pulse fullness, bloodpressure, and signs of peripheral perfusion. Signs of inadequate circulation includetachycardia, weak or unpalpable peripheral pulses, hypotension, and pale, cool, orcyanotic extremities. The first priority in restoring adequate circulation is to stop
  6. 6. bleeding; the second priority is to replace intravascular volume. Cardiac arrestduring transport to the hospital or shortly after arrival following penetrating chestinjuries and possibly blunt chest is an indication for emergency room thoracotomy(ERT). The latter, which is also called resuscitative thoracotomy, allows rapidcontrol of obvious bleeding, opens the pericardium, and allows suturing of cardiacinjuries and cross-clamping of the aorta above the diaphragm. Some traumasurgeons also advocate ERT for cardiac arrest during transport or shortly afterarrival at the hospital following penetrating or blunt injuries to the abdomen.Pregnant patients at term who are in cardiac arrest or shock often can beresuscitated properly only after delivery of the baby.Hemorrhage Obvious sites of hemorrhage should be identified and controlled with directpressure on the wound. Bleeding from the extremities is easily controlled withpressure dressings and packs; tourniquets can cause reperfusion injuries. Bleedingdue to chest trauma is usually from intercostal arteries and often slows or stopswhen the lung is expanded following chest tube drainage. Bleeding due tointraabdominal injuries, depending on its severity, may tamponade itself, allowinga variable period of fluid and blood resuscitation while surgical evaluation iscompleted. Pneumatic antishock garments can decrease bleeding in the abdomenand lower extremities, increase peripheral vascular resistance, and augmentperfusion of the heart and brain. Bleeding wounds above the level of the suit (egthorax or head) contraindicate the use of these garments because of the risk ofincreasing hemorrhage. The term shock denotes circulatory failure leading to inadequate vital organperfusion and oxygen delivery. Although there are many causes of shock, in thetrauma patient it is usually due to hypovolemia. Physiological responses tohemorrhage range from tachycardia, poor capillary perfusion, and a decrease inpulse pressure to hypotension, tachypnea, and delirium. Serum hematocrit andhemoglobin concentrations are often not accurate indicators of acute blood loss.Peripheral somatic nerve stimulation and massive tissue injury appear toexacerbate the reductions in cardiac output and stroke volume seen in hypovolemicshock. The hemodynamic lability of these patients demands invasive arterial bloodpressure monitoring. In severe hypovolemia, the pulse waveform can almostdisappear during the inspiratory phase of mechanical ventilation. The degree ofhypotension on presentation to the emergency room and operating room correlatesstrongly with the mortality rate.DisabilityEvaluation for disability consists of a rapid neurological assessment. Because thereis usually no time for a Glasgow Coma Scale, the AVPU system is used: awake,verbal response, painful response, and unresponsive.
  7. 7. ExposureThe patient should be undressed to allow examination for injuries. In-lineimmobilization should be used if a neck or spinal cord injury is suspected.Secondary SurveyThe secondary survey begins only when the ABCs are stabilized. In the secondarysurvey, the patient is evaluated from head to toe and the indicated studies (eg,radiographs, laboratory tests, invasive diagnostic procedures) are obtained. Headexamination includes looking for injuries to the scalp, eyes, and ears. Neurologicalexamination includes the Glasgow Coma Scale and evaluation of motor andsensory functions as well as reflexes. Fixed dilated pupils do not necessarily implyirreversible brain damage. The chest is auscultated and inspected again forfractures and functional integrity (flail chest). Diminished breath sounds mayreveal a delayed or enlarging pneumothorax that requires chest tube placement.Similarly, distant heart sounds, a narrow pulse pressure, and distended neck veinsmay signal pericardial tamponade, calling for pericardiocentesis. A normal initialexamination does not definitively eliminate the possibility of these problems.Examination of the abdomen should consist of inspection, auscultation, andpalpation. The extremities are examined for fractures, dislocations, and peripheralpulses. A urinary catheter and nasogastric tube are also normally inserted.Basic laboratory analysis includes a complete blood count (or hematocrit orhemoglobin), electrolytes, glucose, blood urea nitrogen (BUN), and creatinine.Arterial blood gases may also be extremely helpful. A chest X-ray should beobtained in all patients with major trauma. The possibility of cervical spine injuryis evaluated by examining all seven vertebrae in a cross-table lateral radiographand a swimmers view. Although these studies detect 80–90% of fractures, only anormal computed tomographic scan reliably rules out significant cervical spinetrauma. Additional radiographic studies may include skull, pelvic, and long bonefilms. A focused assessment with sonography for trauma (FAST) scan is a rapid,bedside, ultrasound examination performed to identify intraperitoneal hemorrhageor pericardial tamponade. The FAST scan, which has become an extension of thephysical examination of the trauma patient, examines four areas for free fluid:perihepatic/hepatorenal space; perisplenic space; pelvis; and pericardium.Depending on the injuries and the hemodynamic status of the patient, otherimaging techniques (eg, chest computed tomography [CT] or angiography) ordiagnostic tests such as diagnostic peritoneal lavage (DPL) may also be indicated.Tertiary Survey Many trauma centers also advocate a tertiary trauma survey (TTS) to avoidmissed injuries. Between 2% and 50% of traumatic injuries may be missed byprimary and secondary surveys, particularly following blunt multiple trauma (eg,car accident). A tertiary survey is defined as a patient evaluation that identifies and
  8. 8. catalogues all injuries after initial resuscitation and operative interventions. Ittypically occurs within 24 h of injuries. This delayed evaluation normally results ina more awake patient who is able to fully communicate all complaints, moredetailed information on the mechanism of injury, and a detailed examination of themedical record to determine preexisting comorbidities.The tertiary survey occurs prior to discharge to reassess and confirm knowninjuries and identify occult ones. It includes another "head-to-toe examination" anda review of all laboratory and imaging studies. Missed injuries can includeextremity and pelvic fractures, spinal cord and head injuries, and abdominal andperipheral nerve injuries.Anesthetic ConsiderationsGeneral ConsiderationsRegional anesthesia is usually impractical and inappropriate in hemodynamicallyunstable patients with life-threatening injuries.If the patient arrives in the operating room already intubated, correct positioning ofthe endotracheal tube must be verified. Patients with suspected head trauma arehyperventilated to decrease intracranial pressure. Ventilation may be compromisedby pneumothorax, flail chest, obstruction of the endotracheal tube, or directpulmonary injury. If the patient is not intubated the same principles of airway managementdescribed above should be followed in the operating room. If time permits,hypovolemia should be at least partially corrected prior to induction of generalanesthesia. Fluid resuscitation and transfusion should continue throughoutinduction and maintenance of anesthesia. Commonly used induction agents fortrauma patients include ketamine and Na oxybutiras. Studies suggest that evenafter adequate fluid resuscitation, the induction dose requirements for propofol aregreatly (80–90%) reduced in patients with major trauma. Even drugs such asketamine and nitrous oxide, which normally indirectly stimulate cardiac function,can display cardiodepressant properties in patients who are in shock and alreadyhave maximal sympathetic stimulation. Hypotension may also be encounteredfollowing etomidate induction. Maintenance of anesthesia in unstable patients may consist primarily of theuse of muscle relaxants (also called neuromuscular blocking agents), with generalanesthetic agents titrated as tolerated (mean arterial pressure > 50–60 mm Hg) inan effort to provide at least amnesia. Intermittent small doses of ketamine (25 mgevery 15 min) are often well tolerated and may help reduce the incidence of recall,particularly when used with low concentrations of a volatile agent (< 0.5 minimumalveolar concentration). Other adjuncts that may be useful in preventing recallinclude midazolam (intermittent 1 mg) or scopolamine (0.3 mg). Many clinicians
  9. 9. avoid nitrous oxide entirely in these patients because of the possibility of apneumothorax and because it limits inspired oxygen concentration. Obviously,drugs that tend to lower blood pressure (eg, histamine release from atracurium andmivacurium) should generally be avoided in patients in hypovolemic shock. Therate of rise of the alveolar concentration of inhalational anesthetics is greater inshock because of lower cardiac output and increased ventilation. Higher alveolaranesthetic partial pressures lead to higher arterial partial pressures and greatermyocardial depression. Similarly, the effects of intravenous anesthetics areexaggerated as they are injected into a smaller intravascular volume. The key to thesafe anesthetic management of shock patients is to administer small incrementaldoses of whichever agents are selected. Invasive monitoring (direct arterial, central venous, and pulmonary arterypressure monitoring) can be extremely helpful in guiding fluid resuscitation, butinsertion of these monitors should not detract from the resuscitation itself. Serialhematocrits (or hemoglobin), arterial blood gas measurement, and serumelectrolytes (particularly K+) are invaluable in protracted resuscitations.Head and Spinal Cord Trauma Any trauma victim with altered consciousness must be considered to have abrain injury. The level of consciousness is assessed by serial Glasgow Coma Scaleevaluations. Common injuries requiring immediate surgical intervention includeepidural hematoma, acute subdural hematoma, and some penetrating brain injuriesand depressed skull fractures. Other injuries that may be managed conservativelyinclude basilar skull fracture and intracerebral hematoma. Basilar skull fracturesare often associated with bruising on the eyelids ("raccoon eyes") or over themastoid process (Battles sign), and cerebrospinal fluid (CSF) leaks from the ear ornose (CSF rhinorrhea). Other signs of brain damage include restlessness,convulsions, and cranial nerve dysfunction (eg, a nonreactive pupil). The classicCushing triad (hypertension, bradycardia, and respiratory disturbances) is a lateand unreliable sign that usually just precedes brain herniation. Hypotension israrely due to head injury alone. Patients suspected of sustaining head traumashould not receive any premedication that will alter their mental status (eg,sedatives, analgesics) or neurological examination (eg, anticholinergic-inducedpupillary dilation). Brain injuries are often accompanied by increased intracranial pressure fromcerebral hemorrhage or edema. Intracranial hypertension is controlled by acombination of fluid restriction (except in the presence of hypovolemic shock),diuretics (eg, mannitol, 0.5 g/kg), barbiturates, and deliberate hypocapnia (PaCO2of 28–32 mm Hg). The latter two require endotracheal intubation, which alsoprotects against aspiration caused by altered airway reflexes. Hypertension ortachycardia during intubation can be attenuated with intravenous lidocaine orfentanyl. Awake intubations cause a precipitous rise in intracranial pressure. Nasal
  10. 10. passage of an endotracheal tube or nasogastric tube in patients with basal skullfractures risks cribriform plate perforation and CSF infection. A slight elevation ofthe head will improve venous drainage and decrease intracranial pressure. The roleof corticosteroids in head injury is controversial; most studies have shown either anadverse effect or no benefit. Anesthetic agents that increase intracranial pressureshould be avoided (eg, ketamine). Hyperglycemia should also be avoided andtreated with insulin if present. Mild hypothermia may prove beneficial in a patientwith a head injury because of its proven value in preventing ischemia-inducedinjury. Because autoregulation of cerebral blood flow is usually impaired in areas ofbrain injury, arterial hypertension can worsen cerebral edema and increaseintracranial pressure. In addition, episodes of arterial hypotension will causeregional cerebral ischemia. In general, cerebral perfusion pressure (the differencebetween mean arterial pressure at the level of the brain and the larger of centralvenous pressure or intracranial pressure) should be maintained above 60 mm Hg. Patients with severe head injuries are more prone to arterial hypoxemia frompulmonary shunting and ventilation/perfusion mismatching. These changes may bedue to aspiration, atelectasis, or direct neural effects on the pulmonary vasculature.Intracranial hypertension may predispose patients to pulmonary edema because ofan increase in sympathetic outflow. The degree of physiological derangement following spinal cord injury isproportional to the level of the lesion. Great care must be taken to prevent furtherinjury during transportation and intubation. Lesions of the cervical spine mayinvolve the phrenic nerves (C3–C5) and cause apnea. Loss of intercostal functionlimits pulmonary reserve and the ability to cough. High thoracic injuries willeliminate sympathetic innervation of the heart (T1–T4), leading to bradycardia.Acute high spinal cord injury can cause spinal shock, a condition characterized byloss of sympathetic tone in the capacitance and resistance vessels below the levelof the lesion, resulting in hypotension, bradycardia, areflexia, and gastrointestinalatony. In fact, venous distention in the legs is a sign of spinal cord injury.Hypotension in these patients requires aggressive fluid therapy—tempered by thepossibility of pulmonary edema after the acute phase has resolved. Succinylcholineis reportedly safe during the first 48 h following the injury but is associated withlife-threatening hyperkalemia afterward. Short-term high-dose corticosteroidtherapy with methylprednisolone (30 mg/kg followed by 5.4 mg/kg/h for 23 h)improves the neurological outcome of patients with spinal cord trauma. Autonomichyperreflexia is associated with lesions above T5 but is not a problem during acutemanagement.Chest Trauma
  11. 11. Trauma to the chest may severely compromise the function of the heart orlungs, leading to cardiogenic shock or hypoxia. A simple pneumothorax is anaccumulation of air between the parietal and visceral pleura. The ipsilateralcollapse of lung tissue results in a severe ventilation/perfusion abnormality andhypoxia. The overlying chest wall is hyperresonant to percussion, breath soundsare decreased or absent, and a chest film confirms lung collapse. Nitrous oxide willexpand a pneumothorax and is contraindicated in these patients. Treatmentincludes placement of a chest tube in the fourth or fifth intercostal space, anteriorto the midaxillary line. A persistent air leak following chest tube placement mayindicate injury to a major bronchus. A tension pneumothorax develops from air entering the pleural spacethrough a one-way valve in the lung or chest wall. In either case, air is forced intothe thorax with inspiration but cannot escape during expiration. As a result, theipsilateral lung completely collapses and the mediastinum and trachea are shiftedto the contralateral side. A simple pneumothorax may develop into a tensionpneumothorax when positive-pressure ventilation is instituted. Venous return andexpansion of the contralateral lung are impaired. Clinical signs include ipsilateralabsence of breath sounds and hyperresonance to percussion, contralateral trachealshift, and distended neck veins. Insertion of a 14-gauge over-the-needle catheter(3–6 cm long) into the second intercostal space at the midclavicular line willconvert a tension pneumothorax to an open pneumothorax. Definitive treatmentincludes chest tube placement as described above. Multiple rib fractures may compromise the functional integrity of the thorax,resulting in flail chest. Hypoxia is often worsened in these patients by underlyingpulmonary contusion or hemothorax. Pulmonary contusion results in worseningrespiratory failure over time. Hemothorax is differentiated from pneumothorax bydullness to percussion over silent lung fields. Hemomediastinum, like hemothorax,can also result in hemorrhagic shock. Massive hemoptysis may require isolation ofthe affected lung with a double-lumen tube (DLT) to prevent blood from enteringthe healthy lung. Use of a single-lumen endotracheal tube with a bronchial blockermay be safer whenever laryngoscopy is difficult or problems are encountered withthe DLT. A large bronchial injury also requires lung separation and ventilation ofthe unaffected side only. High-frequency jet ventilation may alternately be used toventilate at lower airway pressures and help minimize the bronchial air leak whenthe bronchial leak is bilateral or the lung separation is not possible. Air leakagefrom traumatized bronchi can track an open pulmonary vein causing pulmonaryand systemic air embolism. The source of the leak must be quickly identified andcontrolled. Most bronchial ruptures are within 2.5 cm of the carina. Cardiac tamponade is a life-threatening chest injury that must be recognizedearly. When a FAST scan or bedside echocardiography is not available, thepresence of Becks triad (neck vein distention, hypotension, and muffled hearttones), pulsus paradoxus (a > 10 mm Hg decline in blood pressure during
  12. 12. spontaneous inspiration), and a high index of suspicion will help make thediagnosis. Pericardiocentesis provides temporary relief. This is performed bydirecting a 16-gauge over-the-needle catheter (at least 15 cm long) from thexiphochondral junction toward the tip of the left scapula at a 45° angle, under theguidance of transthoracic echocardiography or the electrocardiogram.Electrocardiographic changes during pericardiocentesis indicate overadvancementof the needle into the myocardium. Definitive treatment of pericardial tamponaderequires thoracotomy. Anesthetic management of these patients should maximizecardiac inotropism, chronotropism, and preload. For these reasons, ketamine is afavored induction agent. Penetrating injuries to the heart or great vessels requireimmediate exploration without delay. Repeated manipulation of the heart oftenresults in intermittent episodes of bradycardia and profound hypotension. Myocardial contusion is usually diagnosed by electrocardiographic changesconsistent with ischemia (ST-segment elevation), cardiac enzyme elevations(creatine kinase MB or troponin levels), or an abnormal echocardiogram. Wallmotion abnormalities may be observed with transthoracic echocardiography.Patients are at increased risk for dysrhythmias, such as heart block and ventricularfibrillation. Elective surgery should be postponed until all signs of heart injuryresolve. Other possible injuries following chest trauma include aortic transection oraortic dissection, avulsion of the left subclavian artery, aortic or mitral valvedisruption, traumatic diaphragmatic herniation, and esophageal rupture. Aortictransection usually occurs just distal to the left subclavian artery following a severedeceleration injury; it classically presents as wide mediastinum on the chestradiograph and may be associated with a fracture of the first rib. Acute respiratory distress syndrome (ARDS) is usually a delayed pulmonarycomplication of trauma that has multiple causes: sepsis, direct thoracic injury,aspiration, head injury, fat embolism, massive transfusion, and oxygen toxicity.Clearly, the trauma patient is often at risk for several of these factors. Even withadvances in technology, the mortality rate of ARDS approaches 50%. In somecases, ARDS may present early in the operating room. Similarly, aspirationpneumonia, following aspiration in the field prior to intubation, may first present inthe operating room and could be confused with ARDS. Mechanical ventilators onanesthesia machines are often incapable of sustaining adequate gas flows inpatients who rapidly develop poor lung compliance; use of an intensive care unitventilator capable of sustaining adequate gas flows at high airway pressure may benecessary.Abdominal Trauma Patients involved in major trauma should be considered to have anabdominal injury until proved otherwise. Up to 20% of patients with
  13. 13. intraabdominal injuries do not have pain or signs of peritoneal irritation (muscleguarding, percussion tenderness, or ileus) on first examination. Large quantities ofblood (acute hemoperitoneum) may be present in the abdomen (eg, hepatic orsplenic injury) with minimal signs. Abdominal trauma is usually divided intopenetrating (eg, gunshot or stabbing) and nonpenetrating (eg, deceleration, crush,or compression injuries). Penetrating abdominal injuries are usually obvious with entry marks on theabdomen or lower chest. The most commonly injured organ is the liver. Patientstend to fall into three subgroups: (1) pulseless, (2) hemodynamically unstable, and(3) stable. Pulseless and hemodynamically unstable patients (those who fail tomaintain a systolic blood pressure of 80–90 mm Hg with 1–2 L of fluidresuscitation should be rushed for immediate laparotomy. They usually have eithermajor vascular or solid organ injury. Stable patients with clinical signs ofperitonitis or evisceration should also undergo laparotomy as soon as possible. Incontrast, hemodynamically stable patients with penetrating injuries who do nothave clinical peritonitis require close evaluation to avoid unnecessary laparotomy.Signs of significant intraabdominal injuries may include free air under thediaphragm on the chest X-ray, blood from the nasogastric tube, hematuria, andrectal blood. Further evaluation of hemodynamically stable patients may includeserial physical examinations, local wound exploration, diagnostic peritoneal lavage(DPL), FAST scans, abdominal CT scan, or diagnostic laparoscopy. The use ofFAST scans and abdominal CT has reduced the need for DPLs. Blunt abdominal trauma is the leading cause of morbidity and mortality intrauma, and the leading cause of intraabdominal injuries. Splenic tears or rupturesare most common. A positive FAST scan in a hemodynamically unstable patientwith blunt abdominal trauma is an indication for immediate surgery. If the FASTscan is negative or equivocal in an unstable patient, particularly without peritonealsigns, a search is indicated for other sites of blood loss or causes ofnonhemorrhagic shock. Management of hemodynamically stable patients withblunt abdominal trauma is based on the FAST scan. If the FAST scan is positive,the decision to proceed to laparoscopy or laparotomy is usually based on anabdominal CT. If the FAST scan is negative, continued observation with serialexaminations and repeat FAST scans is usually indicated. Profound hypotension may follow opening of the abdomen as thetamponading effect of extravasated blood (and bowel distention) is lost. Whenevertime permits, preparations for immediate fluid and blood resuscitation with a rapidinfusion device should be completed prior to the laparotomy. Nitrous oxide isavoided to prevent worsening of bowel distention. A nasogastric tube (if notalready present) will help prevent gastric dilation but should be placed orally if acribriform plate fracture is suspected. The potential for massive blood transfusionshould be anticipated, particularly when abdominal trauma is associated withvascular, hepatic, splenic, or renal injuries, pelvic fractures, or retroperitoneal
  14. 14. hemorrhage. Transfusion-induced hyperkalemia is equally as lethal asexsanguination and must be treated aggressively. Massive abdominal hemorrhage may require packing of bleeding areasand/or clamping of the abdominal aorta until bleeding sites are identified and theresuscitation can catch up with the blood loss. Prolonged aortic clamping leads toischemic injury to the liver, kidneys, intestines, and, in some instances, acompartment syndrome of the lower extremities; the latter can producerhabdomyolysis and acute renal failure. The use of a mannitol infusion and a loopdiuretic (prior to aortic cross-clamping), along with resuscitation fluid may preventrenal failure in such instances but is controversial. Rapid resuscitation with fluidsand blood products via a rapid transfusion device, together with control of thebleeding, shortens cross-clamp time and likely reduces the incidence of suchcomplications. Progressive bowel edema from injuries and fluid resuscitation may precludeabdominal closure at the end of the procedure. Tight abdominal closures markedlyincrease intraabdominal pressure, resulting in an abdominal compartmentsyndrome that can produce renal and splanchnic ischemia. Oxygenation andventilation are often severely compromised, even with complete muscle paralysis.Oliguria and renal shutdown follow. In such cases, the abdomen should be leftopen (but sterilely covered—often with intravenous bag plastic) for 48–72 h untilthe edema subsides and secondary closure can be undertaken.Extremity TraumaExtremity injuries can be life-threatening because of associated vascular injuriesand secondary infectious complications. Vascular injuries can lead to massivehemorrhage and threaten extremity viability. For example, a femoral fracture canbe associated with 2–3 units of occult blood loss, and closed pelvic fractures cancause even more occult blood loss resulting in hypovolemic shock. Delay oftreatment or indiscriminate positioning can worsen dislocations and furthercompromise neurovascular bundles. Fat emboli are associated with pelvic andlong-bone fractures and may cause pulmonary insufficiency, dysrhythmias, skinpetechiae, and mental deterioration within 1–3 days after the traumatic event. Thelaboratory diagnosis of fat embolism depends on elevation of serum lipase, fat inthe urine, and thrombocytopenia. A compartment syndrome can also occur following large intramuscularhematomas, crush injuries, fractures, and amputation injuries. An increase ininternal fascial pressure together with a reduced arterial pressure results inischemia, tissue hypoxia, and progressive swelling. As previously discussed,rhabdomyolysis and renal failure may result. Reperfusion when blood pressure isrestored can aggravate the injury and edema. The forearm and lower leg are mostat risk. The diagnosis may be made clinically or based on direct measurement of
  15. 15. compartment pressures: greater than 45 mm Hg or within 10–30 mm Hg ofdiastolic blood pressure. Early fasciotomy to save the limb is recommended. Modern surgical techniques frequently allow the reimplantation of severedextremities and digits. A cooled, amputated, limb part may be reimplanted up to 20h following amputation; a noncooled part has to be implanted within 6 h. If theinjury is isolated, a regional technique (eg, brachial or interscalene plexus block) isoften recommended to increase peripheral blood flow by interrupting sympatheticinnervation. During general anesthesia, the patient should be kept warm, andemergence shivering must be avoided to maximize perfusion.
  16. 16. Anesthesia for Thoracic Surgery Indications and techniques for thoracic surgery have continually evolvedsince its origins. Common indications are no longer restricted to complications oftuberculosis and suppurative pneumonitis but now include thoracic malignancies(mainly of the lungs and esophagus), chest trauma, esophageal disease, andmediastinal tumors. Diagnostic procedures such as bronchoscopy,mediastinoscopy, and open-lung biopsies are also common. Anesthetic techniquesfor separating the ventilation to each lung have allowed the refinement of surgicaltechniques to the point that many procedures are increasingly performedthoracoscopically. High-frequency jet ventilation and cardiopulmonary bypass(CPB) now allow complex procedures such as tracheal resection and lungtransplantation, respectively, to be performed. Thoracic surgery presents a unique set of physiological problems for theanesthesiologist that requires special consideration. These include physiologicalderangements caused by placing the patient with one side down (lateral decubitusposition), opening the chest (open pneumothorax), and the frequent need for one-lung ventilation.The Lateral Decubitus Position The lateral decubitus position provides optimal access for most operationson the lungs, pleura, esophagus, the great vessels, other mediastinal structures, andvertebrae. Unfortunately, this position may significantly alter the normalpulmonary ventilation/perfusion relationships. These derangements are furtheraccentuated by induction of anesthesia, initiation of mechanical ventilation,neuromuscular blockade, opening the chest, and surgical retraction. Althoughperfusion continues to favor the dependent (lower) lung, ventilation progressivelyfavors the less perfused upper lung. The resulting mismatch markedly increases therisk of hypoxemia. The effect of anesthesia on lung compliance in the lateraldecubitus position: the upper lung assumes a more favorable position and the lowerlung becomes less compliant.Positive-Pressure Ventilation Controlled positive-pressure ventilation favors the upper lung in the lateralposition because it is more compliant than the lower one. Neuromuscular blockadeenhances this effect by allowing the abdominal contents to rise up further againstthe dependent hemidiaphragm and impede ventilation of the lower lung. Using arigid "bean bag" to maintain the patient in the lateral decubitus position furtherrestricts movement of the dependent hemithorax. Finally, opening thenondependent side of the chest further accentuates differences in compliancebetween the two sides because the upper lung is now less restricted in movement.
  17. 17. All these effects worsen ventilation/perfusion mismatching and predispose tohypoxemia.The Open Pneumothorax The lungs are normally kept expanded by a negative pleural pressure—thenet result of the tendency of the lung to collapse and the chest wall to expand.When one side of the chest is opened, the negative pleural pressure is lost and theelastic recoil of the lung on that side tends to collapse it. Spontaneous ventilationwith an open pneumothorax in the lateral position results in paradoxicalrespirations and mediastinal shift. These two phenomena can cause progressivehypoxemia and hypercapnia, but, fortunately, their effects are overcome by the useof positive-pressure ventilation during general anesthesia and thoracotomy.Mediastinal Shift During spontaneous ventilation in the lateral position, inspiration causespleural pressure to become more negative on the dependent side but not on the sideof the open pneumothorax. This results in a downward shift of the mediastinumduring inspiration and an upward shift during expiration. The major effect of themediastinal shift is to decrease the contribution of the dependent lung to the tidalvolume.Spontaneous ventilation in a patient with an open pneumothorax also results in to-and-from gas flow between the dependent and nondependent lung (paradoxicalrespiration [pendeluft]). During inspiration, the pneumothorax increases, and gasflows from the upper lung across the carina to the dependent lung. Duringexpiration, the gas flow reverses and moves from the dependent to the upper lung.One-Lung Ventilation Intentional collapse of the lung on the operative side facilitates most thoracicprocedures but greatly complicates anesthetic management. Because the collapsedlung continues to be perfused and is deliberately no longer ventilated, the patientdevelops a large right-to-left intrapulmonary shunt (20–30%). During one-lungventilation, the mixing of unoxygenated blood from the collapsed upper lung withoxygenated blood from the still-ventilated dependent lung widens the PA–a(alveolar-to-arterial) O2 gradient and often results in hypoxemia. Fortunately,blood flow to the nonventilated lung is decreased by hypoxic pulmonaryvasoconstriction (HPV) and possibly surgical compression of the upper lung. Factors known to inhibit HPV and thus worsen the right-to-left shuntinginclude (1) very high or very low pulmonary artery pressures; (2) hypocapnia; (3)high or very low mixed venous PO2; (4) vasodilators such as nitroglycerin,nitroprusside, adrenergic agonists (including dobutamine and salbutamol), andcalcium channel blockers; (5) pulmonary infection; and (6) inhalation anesthetics.
  18. 18. Factors that decrease blood flow to the ventilated lung can be equallydetrimental; they counteract the effect of HPV by indirectly increasing blood flowto the collapsed lung. Such factors include (1) high mean airway pressures in theventilated lung due to high positive end-expiratory pressure (PEEP),hyperventilation, or high peak inspiratory pressures; (2) a low FIO2, whichproduces hypoxic pulmonary vasoconstriction in the ventilated lung; (3)vasoconstrictors that may have a greater effect on normoxic vessels than hypoxicones; and (4) intrinsic PEEP that develops due to inadequate expiratory times. Elimination of CO2 is usually not affected by one-lung ventilation providedminute ventilation is unchanged and preexisting CO2 retention was not presentwhile ventilating both lungs; arterial CO2 tension is usually not appreciably alteredPostoperative Management Most patients are extubated early to decrease the risk of pulmonarybarotrauma (particularly "blowout" [rupture] of the bronchial suture line) andpulmonary infection. Patients with marginal pulmonary reserve should be leftintubated until standard extubation criteria are met; if a double-lumen tube wasused for one-lung ventilation, it should be replaced with a regular single-lumentube at the end of surgery. A catheter guide ("tube exchanger") should be used ifthe original laryngoscopy was difficult (above). Patients are observed carefully in the intensive care unit (ICU) in mostinstances, at least overnight or longer Postoperative hypoxemia and respiratoryacidosis are common. These effects are largely caused by atelectasis from surgicalcompression of the lungs and "shallow breathing (splinting)" due to incisionalpain. Gravity-dependent transudation of fluid into the dependent lung (above) mayalso be contributory. Reexpansion edema of the collapsed nondependent lung canalso occur, particularly with rapid reinflation of the lung. Postoperative hemorrhage complicates about 3% of thoracotomies and maybe associated with up to 20% mortality. Signs of hemorrhage include increasedchest tube drainage (> 200 mL/h), hypotension, tachycardia, and a fallinghematocrit. Postoperative supraventricular tachyarrhythmias are common andshould be treated aggressively. Acute right ventricular failure is suggested by a lowcardiac output, elevated CVP, oliguria, and a normal pulmonary capillaryocclusion pressure.Routine postoperative care should include maintenance of a semiupright (> 30°)position, supplemental oxygen (40–50%), incentive spirometry, closeelectrocardiographic and hemodynamic monitoring, a postoperative radiograph,and aggressive pain relief.Postoperative Analgesia
  19. 19. The balance between comfort and respiratory depression in patients withmarginal lung function is difficult to achieve with parenteral opioids alone.Patients who have undergone thoracotomy clearly benefit from the use of othertechniques described below that may obviate the need for any parenteral opioids. Ifparenteral opioids are used alone, small intravenous doses are superior to largeintramuscular doses and probably are best administered via a patient-controlledanalgesia (PCA) device. A long-acting agent such as 0.5% ropivacaine (4–5 mL), injected two levelsabove and below the thoracotomy incision, typically provides excellent pain relief.These blocks may be done under direct vision intraoperatively or via the standardtechnique postoperatively. Intercostal or paravertebral nerve blocks improvepostoperative arterial blood gases and pulmonary function tests and shortenhospital stay. Epidural opioids with or without a local anesthetic can also provide excellentanalgesia. Equally satisfactory analgesia may be obtained with either a lumbar orthoracic epidural catheter when morphine is used. Injection of morphine 5–7 mg in10–15 mL of saline usually provides 6–24 h of analgesia without autonomic,sensory, or motor blockade. The lumbar route may be safer because it is less likelyto traumatize the spinal cord or puncture the dura, but the latter is more of atheoretical concern because it may occur (although infrequently) during cautiousand correct placement of a thoracic epidural. Epidural injections of a lipophilicopioid, such as fentanyl, are more effective via a thoracic catheter than a lumbarcatheter. Some clinicians prefer fentanyl given epidurally because it is less likelyto cause delayed respiratory depression. In either case, patients should be closelymonitored for this complication.Postoperative Complications Postoperative complications following thoracotomy are relatively common,but fortunately most are minor and resolve uneventfully. Blood clots and thicksecretions readily obstruct the airways and result in atelectasis; aggressive butgentle suctioning may be necessary. Significant atelectasis is suggested by trachealdeviation and shifting of the mediastinum to the operative side followingsegmental or lobar resections. Therapeutic bronchoscopy should be considered forpersistent atelectasis, particularly when associated with thick secretions. Air leaksfrom the operative hemithorax are common following segmental and lobarresections because fissures are usually incomplete; resection therefore often leavesthe small channels responsible for collateral ventilation open. Most air leaks stopafter a few days. Bronchopleural fistula presents as a sudden large air leak from thechest tube that may be associated with an increasing pneumothorax and partiallung collapse. When it occurs within the first 24–72 h, it is usually the result ofinadequate surgical closure of the bronchial stump. Delayed presentation is usually
  20. 20. due to necrosis of the suture line associated with inadequate blood flow orinfection. Some complications are rare but deserve special consideration because theycan be life-threatening, require a high index of suspicion, and may requireimmediate exploratory thoracotomy. Postoperative bleeding was discussed above.Torsion of a lobe or segment can occur as the remaining lung on the operative sideexpands to occupy the hemithorax. The torsion usually occludes the pulmonaryvein to that part of the lung, causing venous outflow obstruction. Hemoptysis andinfarction can rapidly follow. The diagnosis is suggested by an enlarginghomogeneous density on the chest radiograph and a closed lobar orifice onbronchoscopy. Acute herniation of the heart into the operative hemithorax canoccur through the pericardial defect that may be left following a radicalpneumonectomy. A large pressure differential between the two hemithoraxes isthought to trigger this catastrophic event. Herniation into the right hemithoraxresults in sudden severe hypotension with an elevated CVP because of torsion ofthe central veins. Herniation into the left hemithorax following leftpneumonectomy results in sudden compression of the heart at the atrioventriculargroove, resulting in hypotension, ischemia, and infarction. A chest radiographshows a shift of the cardiac shadow into the operative hemithorax. Extensive mediastinal dissections can injure the phrenic, vagus, and leftrecurrent laryngeal nerves. Postoperative phrenic nerve palsy presents as elevationof the ipsilateral hemidiaphragm together with difficulty in weaning the patientfrom the ventilator. Large en bloc chest wall resections may also involve part ofthe diaphragm, causing a similar problem, in addition to a flail chest. Paraplegiacan rarely follow thoracotomy for lung resection. Sacrificing the left lowerintercostal arteries can produce spinal cord ischemia. Alternately, an epiduralhematoma may form if the surgical dissection enters the epidural space through thechest cavity. Anesthesia for Orthopedic Surgery Orthopedic surgery challenges the anesthesiologist with its diversity. Thedegree of surgical trespass varies from minor finger surgery to hemipelvectomy.Orthopedic patients range from neonates with congenital anomalies to healthyyoung athletes to immobile geriatric patients with end-stage multiorgan failure.Long bone fractures predispose to fat embolism syndrome. Patients may be at highrisk for venous thromboembolism, particularly following pelvic, hip, and kneeoperations. Use of bone cement during arthroplasties can cause hemodynamicinstability. Limb tourniquets limit blood loss but introduce additional risks.Neuraxial and other regional anesthetic techniques play an important role indecreasing the incidence of perioperative thromboembolic complications,providing postoperative analgesia, and facilitating early rehabilitation and hospitaldischarges. Advances in surgical techniques, such as minimally invasive
  21. 21. approaches to hip replacement utilizing computer-assisted surgery, arenecessitating modifications in anesthetic management to allow for overnight oreven same day discharge of patients undergoing procedures that used to require aweek or more in the hospital. After reviewing problems that are frequentlyencountered in orthopedic surgery, this chapter discusses the anestheticmanagement of patients undergoing some common orthopedic operations.Special Considerations in Orthopedic SurgeryBone Cement Bone cement, polymethylmethacrylate, is frequently required for jointarthroplasties. The cement interdigitates within the interstices of cancellous boneand strongly binds the prosthetic device to the patients bone. Mixing polymerizedmethylmethacrylate powder with liquid methylmethacrylate monomer causespolymerization and cross-linking of the polymer chains. This exothermic reactionleads to hardening of the cement and expansion against the prosthetic components.The resultant intramedullary hypertension (> 500 mm Hg) causes embolization offat, bone marrow, cement, and air into the femoral venous channels. Residualmethylmethacrylate monomer can produce vasodilation and a decrease in systemicvascular resistance. The release of tissue thromboplastin may trigger plateletaggregation, microthrombus formation in the lungs, and cardiovascular instabilityas a result of the circulation of vasoactive substances.The clinical manifestations of bone cement implantation syndrome includehypoxia (increased pulmonary shunt), hypotension, dysrhythmias (including heartblock and sinus arrest), pulmonary hypertension (increased pulmonary vascularresistance), and decreased cardiac output. Emboli most frequently occur duringinsertion of a femoral prosthesis. Strategies to minimize the effects of thiscomplication include increasing inspired oxygen concentration prior to cementing,maintaining euvolemia by monitoring central venous pressure, creating a vent holein the distal femur to relieve intramedullary pressure, performing high-pressurelavage of the femoral shaft to remove debris (potential microemboli), or using anuncemented femoral component.Another major disadvantage of cement is the potential for gradual loosening of theprosthesis resulting from breakage of small pieces of cement over the years.Components of cementless implants are made of a porous material that allows thenatural bone to grow into them. Cementless prostheses generally last longer andmay be advantageous for younger, active patients, even though full recovery maybe longer compared to cemented joint replacements. Unfortunately, cementlessimplants require healthy active bone formation. Therefore cemented prosthesis arestill preferred for older (> 80 years) and less active patients who often haveosteoporosis and/or thin bone (cortex). Practices continue to evolve regardingselection of cemented versus cementless joint replacements, depending on the joint
  22. 22. replaced, patient, and surgical technique. In many cases cemented and cementlesscomponents are used in the same patient (eg, total hip arthroplasty). Articularsurfaces on modern prostheses may be metal, plastic, or ceramic.Pneumatic Tourniquets Use of a pneumatic tourniquet on the upper or lower extremity creates abloodless field that greatly facilitates surgery. Unfortunately, tourniquets areassociated with potential problems of their own, including hemodynamic changes,pain, metabolic alterations, arterial thromboembolism, and even pulmonaryembolism. Inflation pressure is usually about 100 mm Hg over systolic bloodpressure. Prolonged inflation (> 2 h) routinely leads to transient muscledysfunction and may be associated with permanent peripheral nerve injury or evenrhabdomyolysis. Tourniquet inflation has also been associated with increases inbody temperature in pediatric patients undergoing leg surgery. Exsanguination of a lower extremity and tourniquet inflation cause a shift ofblood volume into the central circulation. Although this is usually not clinicallysignificant, bilateral Esmarch bandage exsanguination can cause a rise in centralvenous pressure and arterial blood pressure that may not be well tolerated inpatients with left ventricular dysfunction. Anyone who has had a tourniquet on the thigh inflated to 100 mm Hg abovesystolic blood pressure for more than a few minutes appreciates tourniquet pain.Although the mechanism and neural pathways for this severe aching and burningsensation defy precise explanation, unmyelinated, slow-conduction C fibers, whichare relatively resistant to local anesthetic blockade, probably play a critical role.Tourniquet pain gradually becomes so severe over time that patients may requiresubstantial supplemental analgesia, if not general anesthesia, despite a regionalblock that is adequate for surgical incision. Even during general anesthesia,tourniquet pain is often manifested as a gradually increasing mean arterial bloodpressure beginning about ¾ to 1 h after cuff inflation. Signs of progressivesympathetic activation include marked hypertension, tachycardia, and diaphoresis.The likelihood of tourniquet pain and its accompanying hypertension may beinfluenced by many factors, including anesthetic technique (intravenous regional >epidural > spinal > general anesthesia), intensity and level of regional anestheticblock, choice of local anesthetic (hyperbaric spinal with tetracaine > isobaricbupivacaine), and supplementation of the block with opioids. Cuff deflation invariably and immediately relieves the sensation oftourniquet pain and its hypertension. In fact, cuff deflation can be accompanied bya significant fall in central venous pressure and arterial blood pressure. Heart rateusually increases and core temperature decreases. Washout of accumulatedmetabolic wastes in the ischemic extremity increases PaCO2, ETCO2, and serumlactate and potassium levels. These metabolic alterations can cause an increase in
  23. 23. minute ventilation in the spontaneously breathing patient and, rarely,dysrhythmias. Ironically, cuff deflation and blood reoxygenation have beendemonstrated to worsen ischemic tissue injury due to the formation of lipidperoxides. This reperfusion injury may be attenuated by propofol, which has beenreported to limit superoxide generation. Tourniquet-induced ischemia of a lower extremity may lead to thedevelopment of deep venous thrombosis. Transesophageal echocardiography hasdetected subclinical pulmonary embolism (miliary emboli) following tourniquetdeflation in cases as minor as diagnostic knee arthroscopy. Rare episodes ofmassive pulmonary embolism during total knee arthroplasty have been reportedduring leg exsanguination, after tourniquet inflation, and following tourniquetdeflation. Tourniquets are generally contraindicated in patients with significantcalcific arterial disease. They have been safely used in patients with sickle celldisease, although particular attention should be paid to maintaining oxygenation,normocarbia or hypocarbia, hydration, and normothermia.Fat Embolism SyndromeAlthough some degree of fat embolism probably occurs in all cases of long-bonefracture, fat embolism syndrome is a less frequent but potentially fatal (10–20%mortality) event that can complicate anesthetic management. Fat embolismsyndrome classically presents within 72 h following long-bone or pelvic fracture,with the triad of dyspnea, confusion, and petechiae. This syndrome can also beseen following cardiopulmonary resuscitation, parental feeding with lipid infusion,and liposuction. Two theories have been proposed for its pathogenesis. The mostpopular theory holds that fat globules are released by the disruption of fat cells inthe fractured bone and enter the circulation through tears in medullary vessels. Analternative theory proposes that the fat globules are chylomicrons resulting fromthe aggregation of circulating free fatty acids caused by changes in fatty acidmetabolism. Regardless of their source, the increased free fatty acid levels canhave a toxic effect on the capillary–alveolar membrane leading to the release ofvasoactive amines and prostaglandins and the development of acute respiratorydistress syndrome. Neurological manifestations (agitation, confusion, stupor, orcoma) probably represent capillary damage to the cerebral circulation and cerebraledema and may be exacerbated by hypoxia. The diagnosis of fat embolism syndrome is suggested by petechiae on thechest, upper extremities, axillae, and conjunctiva. Fat globules may be found in theretina, urine, or sputum. Coagulation abnormalities such as thrombocytopenia orprolonged clotting times are occasionally present. Serum lipase activity may beelevated, but bears no relationship to disease severity. Pulmonary involvementtypically progresses from mild hypoxia and a normal chest radiograph to severehypoxia and a chest film showing diffuse patchy pulmonary infiltrates. Most of theclassic signs and symptoms of fat embolism syndrome occur 1–3 days after the
  24. 24. precipitant event. Signs during general anesthesia may include a decline in ETCO2and arterial oxygen saturation or a rise in pulmonary artery pressures.Electrocardiography may show ischemic-appearing ST-segment changes and right-sided heart strain. Treatment is 2-fold: prophylactic and supportive. Early stabilization of thefracture decreases the incidence of fat embolism syndrome. Supportive treatmentconsists of oxygen therapy with continuous positive airway pressure ventilation.Treatment with heparin or alcohol has generally been disappointing. High-dosecorticosteroid therapy may be beneficial, particularly in the presence of cerebraledema.Deep Venous Thrombosis and Thromboembolism Deep vein thrombosis (DVT) and pulmonary embolism (PE) can be majorcauses of morbidity and mortality following orthopedic operations on the pelvisand lower extremities. Additional risk factors include obesity, age > 60 years,procedures lasting > 30 min, use of a tourniquet, lower extremity fracture, andimmobilization for more than 4 days. Patients at highest risk are those undergoinghip surgery and knee reconstruction, where DVT rates in older studies were as highas 50%. The incidence of clinically significant pulmonary embolism following hipsurgery in some studies was reported to be as high as 20%, whereas that of fatalpulmonary embolism was as much as 1–3%. Major pathophysiologicalmechanisms likely include venous stasis and a hypercoagulable state due tolocalized and systemic inflammatory responses to surgery. Prophylacticanticoagulation and use of intermittent pneumatic (leg) compression (IPC) deviceshave been shown to significantly decrease the incidence of DVT and PE. Although most clinicians agree that full anticoagulation or fibrinolytictherapy (eg, urokinase) represents an unacceptable risk for spinal or epiduralhematoma following neuraxial anesthesia, the danger for patients already receivinglow-dose anticoagulation preoperatively is somewhat controversial. Placement ofan epidural needle or catheter (or removal) should generally not be undertakenwithin 6–8 h of a subcutaneous "minidose" of unfractionated heparin, or within12–24 h of LMWH. Although potentially less traumatic, spinal anesthesia mayrepresent a similar risk. Concomitant administration of an antiplatelet agent mayfurther increase the risk of a spinal hematoma. Another major concern is that aregional anesthetic could mask the hallmarks of an expanding hematoma andspinal cord compression (eg, lower back pain and lower extremity weakness), thusdelaying diagnosis and treatment. Obstetric Anesthesia Obstetric anesthesia is a demanding but gratifying subspecialty ofanesthesiology. The widespread acceptance and use of regional anesthesia forlabor has made obstetric anesthesia a major part of most anesthetic practices. The
  25. 25. guidelines of the American College of Obstetricians and Gynecologists andAmerican Society of Anesthesiologists require that anesthesia service be readilyavailable continuously and that cesarean section be started within 30 min of therecognition for its need. Moreover, high-risk patients, such as those undergoing atrial of vaginal birth after a previous cesarean delivery (VBAC), may require theimmediate availability of anesthesia services. Although most parturients are young and healthy, they nonetheless representa high-risk group of patients for all the reasons discussed in the preceding chapter.Anesthesia for Labor and Vaginal DeliveryPsychological and Nonpharmacological Techniques Psychological and nonpharmacological techniques are based on the premisethat the pain of labor can be suppressed by reorganizing ones thoughts. Patienteducation and positive conditioning about the birthing process are central to suchtechniques. Pain during labor tends to be accentuated by fear of the unknown orprevious unpleasant experiences. The parturient also concentrates on an object inthe room and attempts to focus her thoughts away from the pain. Less commonnonpharmacological techniques include hypnosis, transcutaneous electrical nervestimulation, biofeedback, and acupuncture. The success of all these techniquesvaries considerably from patient to patient, but most patients require additionalforms of pain relief.Parenteral Agents Nearly all parenteral opioid analgesics and sedatives readily cross theplacenta and can affect the fetus. Concern over fetal depression limits the use ofthese agents to the early stages of labor or to situations in which regional anesthetictechniques are not available. Central nervous system depression in the neonate maybe manifested by a prolonged time to sustain respirations, respiratory acidosis, oran abnormal neurobehavioral examination. Moreover, loss of beat-to-beatvariability in the fetal heart rate (seen with most central nervous systemdepressants) and decreased fetal movements (due to sedation of fetus) complicatethe evaluation of fetal well-being during labor. Long-term fetal heart variability isaffected more than short-term variability. The degree and significance of theseeffects depend on the specific agent, the dose, the time elapsed between itsadministration and delivery, and fetal maturity. Premature neonates exhibit thegreatest sensitivity. In addition to maternal respiratory depression, opioids can alsoinduce maternal nausea and vomiting and delay gastric emptying. Intravenous fentanyl, 25–100 mkg/h, has also been used for labor. Fentanylin 25–100 mkg doses has a 3- to 10-min analgesic onset that initially lasts about 60min, and lasts longer following multiple doses. However, maternal respiratorydepression outlasts the analgesia. Lower doses of fentanyl may be associated with
  26. 26. little or no neonatal respiratory depression and are reported to have no effect onApgar scores. Morphine is not used because in equianalgesic doses it appears tocause greater respiratory depression in the fetus than meperidine and fentanyl. Benzodiazepines, particularly longer acting agents such as diazepam, are notused during labor because of their potential to cause prolonged neonataldepression. The amnestic properties of benzodiazepines make them undesirableagents for parturients because they usually want to remember the experience ofdelivery. Low-dose intravenous ketamine is a powerful analgesic. In doses of 10–15mg intravenously, good analgesia can be obtained in 2–5 min without loss ofconsciousness. Unfortunately, fetal depression with low Apgar scores is associatedwith doses greater than 1 mg/kg. Large boluses of ketamine (> 1 mg/kg) can beassociated with hypertonic uterine contractions. Low-dose ketamine is most usefuljust prior to delivery or as an adjuvant to regional anesthesia. Some cliniciansavoid use of ketamine because it may produce unpleasant psychotomimetic effects.Pudendal Nerve Block Pudendal nerve blocks are often combined with perineal infiltration of localanesthetic to provide perineal anesthesia during the second stage of labor whenother forms of anesthesia are not employed or prove to be inadequate. Paracervicalplexus blocks are no longer used because of their association with a relatively highrate of fetal bradycardia; the close proximity of the injection site (paracervicalplexus or Frankenhäusers ganglia) to the uterine artery can result in uterine arterialvasoconstriction, uteroplacental insufficiency, and high levels of the localanesthetic in the fetal blood.Regional Anesthetic Techniques Regional techniques employing the epidural or intrathecal route, alone or incombination, are currently the most popular methods of pain relief during laborand delivery. They can provide excellent pain relief, yet allow the mother to beawake and cooperative during labor. Although spinal opioids or local anestheticsalone can provide satisfactory analgesia, techniques that combine the two haveproved to be the most satisfactory in most parturients. Moreover, the apparentsynergy between the two types of agents decreases dose requirements and providesexcellent analgesia with few maternal side effects and little or no neonataldepression.Spinal Opioids Alone Preservative-free opioids may be given intraspinally as a single injection orintermittently via an epidural or intrathecal catheter. Relatively high doses arerequired for analgesia during labor when spinal opioids are used alone. For
  27. 27. example, the ED50 during labor is 124 mkg for epidural fentanyl and 21 mkg forepidural sufentanil. The higher doses may be associated with a high risk of sideeffects, most importantly respiratory depression. For that reason combinations oflocal anesthetics and opioids are most commonly used.Intrathecal Opioids Intrathecal morphine in doses of 0.25–0.5 mg may produce satisfactory andprolonged (4–6 h) analgesia during the first stage of labor. Unfortunately, the onsetof analgesia is slow (45–60 min), and these doses may not be sufficient in manypatients. Higher doses are associated with a relatively high incidence of sideeffects. Morphine is therefore rarely used alone. The combination of morphine,0.25 mg, and fentanyl, 12.5 mkg, (or sufentanil, 5 mkg) may result in a more rapidonset of analgesia (5 min). Early reports of fetal bradycardia following intrathecalopioid injections (eg, sufentanil) are not supported by subsequent studies. Spinalmeperidine has some weak local anesthetic properties and therefore can decreaseblood pressure. Hypotension following intrathecal sufentanil for labor is likelyrelated to the analgesia and decreased circulating catecholamine levels.Epidural Opioids Again relatively high doses (7.5 mg) of morphine are required forsatisfactory analgesia during labor, but doses larger than 5 mg are notrecommended because of the increased risk of delayed respiratory depression andbecause the analgesia is effective only in the early first stage of labor. The onset ofanalgesia may take 30–60 min but lasts up to 12–24 h (as will the risk of delayedrespiratory depression). Epidural fentanyl, 50–150 mkg, or sufentanil, 10–20 mkg,usually produces analgesia within 5–10 min with few side effects, but it has a shortduration (1–2 h). Although "single-shot" epidural opioids do not appear to causesignificant neonatal depression, caution should be exercised following repeatedadministrations. Combinations of a lower dose of morphine, 2.5 mg, with fentanyl,25–50 mkg (or sufentanil, 7.5–10 mkg), may result in a more rapid onset andprolongation of analgesia (4–5 h) with fewer side effects.Local Anesthetic/Local Anesthetic–Opioid Mixtures Epidural and spinal (intrathecal) analgesia more commonly utilizes localanesthetics either alone or with opioids for labor and delivery. Pain relief duringthe first stage of labor requires neural blockade at the T10–L1 sensory level,whereas pain relief during the second stage of labor requires neural blockade atT10–S4. Continuous lumbar epidural analgesia is the most versatile and mostcommonly employed technique, because it can be used for pain relief for the firststage of labor as well as analgesia/anesthesia for subsequent vaginal delivery orcesarean section, if necessary. "Single-shot" epidural, spinal, or combined spinalepidural analgesia may be appropriate when pain relief is initiated just prior tovaginal delivery (the second stage). Obstetric caudal injections have largely been
  28. 28. abandoned because of less versatility (they are most effective for perinealanalgesia/anesthesia), the need for large volumes of local anesthetic, earlyparalysis of the pelvic muscles that may interfere with normal rotation of the fetalhead, and a small risk of accidental puncture of the fetus. Absolute contraindications to regional anesthesia include infection over theinjection site, coagulopathy, thrombocytopenia, marked hypovolemia, trueallergies to local anesthetics, and the patients refusal or inability to cooperate forregional anesthesia. Preexisting neurological disease, back disorders, and someforms of heart disease are relative contraindications. Before performing any regional block, appropriate equipment and suppliesfor resuscitation should be checked and made immediately available. Minimumsupplies include oxygen, suction, a mask with a positive-pressure device forventilation, a functioning laryngoscope, endotracheal tubes (6 or 6.5 mm), oral ornasal airways, intravenous fluids, ephedrine, atropine, thiopental (or propofol), andsuccinylcholine. The ability to frequently monitor blood pressure and heart rate ismandatory. A pulse oximeter and capnograph should also be readily available.Lumbar Epidural Anaglesia Traditionally epidural analgesia for labor is administered only when labor iswell established. However, recent studies suggest that when dilute mixtures of alocal anesthetic and an opioid are used epidural analgesia has little if any effect onthe progress of labor. Concerns about increasing the likelihood of an oxytocinaugmentation, operative (eg, forceps) delivery, or cesarean sections appear to beunjustified. It is often advantageous to place an epidural catheter early, when thepatient is comfortable and can be positioned easily. Moreover, should emergentcesarean section become necessary the presence of a well-functioning epiduralcatheter makes it possible to avoid general anesthesia. Epidural analgesia should generally be initiated when the parturient wants it(on demand) and the obstetrician approves it. A more conservative approach is towait until labor is well established. Although exact criteria vary, commonlyaccepted conservative criteria include no fetal distress; good regular contractions3–4 min apart and lasting about 1 min; adequate cervical dilatation, ie, 3–4 cm; andengagement of the fetal head. Even with a conservative approach, epiduralanesthesia is often administered earlier to parturients who are committed to labor,eg, ruptured membranes and receiving an oxytocin infusion once a goodcontraction pattern is achieved. Some clinicians advocate the midline approach, whereas others favor theparamedian approach. If air is used for detecting loss of resistance, the amountinjected should be limited as much as possible; injection of excessive amounts ofair (> 2–3 mL) in the epidural space has been associated with patchy or unilateralanalgesia and headache. The average depth of the epidural space in obstetric
  29. 29. patients is reported to be 5 cm from the skin. Placement of the epidural catheter atthe L3–4 or L4–5 interspace is generally optimal for achieving a T10–S5 neuralblockade. If unintentional dural puncture occurs, the anesthetist has two choices:(1) place the epidural catheter in the subarachnoid space for continuous spinalanalgesia and anesthesia (see below), or (2) remove the needle and attemptplacement at a higher spinal level.Choice of Local Anesthetic Solutions The addition of opioids to local anesthetic solutions for epidural anesthesiahas dramatically changed the practice of obstetric anesthesia. The synergy betweenepidural opioids and local anesthetic solutions appears to reflect separate sites ofaction, namely, opiate receptors and neuronal axons, respectively. When the twoare combined, very low concentrations of both local anesthetic and opioid can beused. More importantly, the incidence of adverse side effects, such as hypotensionand drug toxicity, is likely reduced. Although local anesthetics can be used alone,there is rarely a reason to do so. Moreover, when an opioid is omitted, the higherconcentration of local anesthetic required (eg, bupivacaine 0.25% and ropivacaine0.2%) can impair the parturients ability to push effectively as the labor progresses.Bupivacaine or ropivacaine in concentrations of 0.0625–0.125% with eitherfentanyl 2–3 mkg/mL or sufentanil 0.3–0.5 mkg/mL is most often used. In general,the lower the concentration of the local anesthetic the higher the concentration ofopioid that is required. Very dilute local anesthetic mixtures (0.0625%) generallydo not produce motor blockade and may allow some patients to ambulate("walking" or "mobile" epidural). The long duration of action of bupivacainemakes it a popular agent for labor. Ropivacaine may be preferable because ofpossibly less motor blockade and its reduced potential for cardiotoxicity. Systemicabsorption of the opioid can decrease fetal heart rate variability due to transientsedation of the fetus. The effect of epinephrine-containing solutions on the course of labor issomewhat controversial. Many clinicians use epinephrine-containing solutionsonly for intravascular test doses because of concern that the solutions may slow theprogression of labor or adversely affect the fetus; others use only very diluteconcentrations of epinephrine such as 1:800,000 or 1:400,000. Studies comparingthese various agents have failed to find any differences in neonatal Apgar scores,acid–base status, or neurobehavioral evaluations.Combined Spinal and Epidural (CSE) Analgesia Techniques using CSE analgesia and anesthesia may particularly benefitpatients with severe pain early in labor and those who receive analgesia/anesthesiajust prior to delivery. Intrathecal opioid and local anesthetic are injected and anepidural catheter is left in place. The intrathecal drugs provide almost immediatepain control and have minimal effects on the early progress of labor, whereas the
  30. 30. epidural catheter provides a route for subsequent analgesia for labor and deliveryor anesthesia for cesarean section. Addition of small doses of local anestheticagents to intrathecal opioid injection greatly potentiates their analgesia and cansignificantly reduce opioid requirements. Thus, many clinicians will inject 2.5 mgof preservative-free bupivacaine or 3–4 mg of ropivacaine with intrathecal opioidsfor analgesia in the first stage of labor. Intrathecal doses for CSE are fentanyl 4–5mkg or sufentanil 2–3 mkg. Addition of 0.1 mg of epinephrine prolongs theanalgesia with such mixtures but not for intrathecal opioids alone. Some studiessuggest that CSE techniques may be associated with greater patient satisfactionthan epidural analgesia alone. A 24- to 27-gauge pencil-point spinal needle is usedto minimize the incidence of PDPH.Spinal Anesthesia Spinal anesthesia given just prior to delivery—also known as saddle block—provides profound anesthesia for operative vaginal delivery. A 500- to 1000-mLfluid bolus is given prior to the procedure, which is performed with the patient inthe sitting position. Use of a 22-gauge or smaller, pencil-point spinal needle(Whitacre, Sprotte, or Gertie Marx) decreases the likelihood of PDPH. Hyperbarictetracaine (3–4 mg), bupivacaine (6–7 mg), or lidocaine (20–40 mg) usuallyprovides excellent perineal anesthesia. Addition of fentanyl 12.5–25 mkg orsufentanil 5–7.5 mkg significantly potentiates the block. A T10 sensory level canbe obtained with slightly larger amounts of local anesthetic. The intrathecalinjection should be given slowly over 30 s and between contractions to minimizeexcessive cephalad spread. Three minutes after injection, the patient is placed inthe lithotomy position with left uterine displacement.General Anesthesia Because of the increased risk of aspiration, general anesthesia for vaginaldelivery is avoided except for a true emergency. If an epidural catheter is alreadyin place and time permits, rapid-onset regional anesthesia can often be obtainedwith alkalinized lidocaine 2% or chloroprocaine 3%. Table 1 lists indications forgeneral anesthesia during vaginal delivery. Many of these indications share theneed for uterine relaxation. Intravenous nitroglycerin, 50–100 mkg, has beenshown to be effective in inducing uterine relaxation and may obviate the need forgeneral anesthesia in these cases.Table 1. Possible Indications for General Anesthesia during Vaginal Delivery.Fetal distress during the second stageTetanic uterine contractionsBreech extraction
  31. 31. Version and extractionManual removal of a retained placentaReplacement of an inverted uterusPsychiatric patients who become uncontrollableSuggested Technique for Vaginal Delivery 1. Place a wedge under the right hip for left uterine displacement. 2. Preoxygenate the patient for 3–5 min as monitors are applied. Defasciculation with a nondepolarizing muscle relaxant is usually not necessary, because most pregnant patients do not fasciculate following succinylcholine. Moreover, fasciculations do not appear to promote regurgitation, because any increase in intragastric pressure is matched by a similar increase in the lower esophageal sphincter. 3. Once all monitors are applied and the obstetrician is ready, proceed with a rapid-sequence induction while cricoid pressure is applied and intubate with a 6- to 6.5-mm endotracheal tube. Propofol, 2 mg/kg, or thiopental, 4 mg/kg, and succinylcholine, 1.5 mg/kg, are most commonly used unless the patient is hypovolemic or hypotensive, in which case ketamine, 1 mg/kg, is used as the induction agent. 4. After successful intubation, use 1–2 minimum alveolar concentration (MAC) of any potent volatile inhalational agent in 100% oxygen while carefully monitoring blood pressure. 5. If skeletal muscle relaxation is necessary, a short- to intermediate-acting, nondepolarizing muscle relaxant (eg, mivacurium or atracurium) is used. 6. Once the fetus and placenta are delivered, the volatile agent is decreased to less than 0.5 MAC or discontinued, an oxytocin infusion is started (20–40 U/L of intravenous fluid), and a nitrous oxide–opioid technique or propofol infusion can be used to avoid recall. 7. An attempt to aspirate gastric contents may be made via an orogastric tube to decrease the likelihood of pulmonary aspiration on emergence. 8. At the end of the procedure, the skeletal nondepolarizing muscle relaxant is reversed, the gastric tube (if placed) is removed, and the patient is extubated while awake.Anesthesia for Cesarean Section The choice of anesthesia for cesarean section is determined by multiplefactors, including the indication for operating, its urgency, patient and obstetricianpreferences, and the skills of the anesthetist. Cesarean section rates betweeninstitutions generally vary between 15 and 25%. Offten it performed underregional anesthesia, nearly evenly split between spinal and epidural anesthesia.Regional anesthesia has become the preferred technique because general
  32. 32. anesthesia has been associated with higher maternal mortality. Deaths associatedwith general anesthesia are generally related to airway problems, such as inabilityto intubate, inability to ventilate, or aspiration pneumonitis, whereas deathsassociated with regional anesthesia are generally related to excessively high neuralblockade or local anesthetic toxicity. Other advantages of regional anesthesia include (1) less neonatal exposure topotentially depressant drugs, (2) a decreased risk of maternal pulmonary aspiration,(3) an awake mother at the birth of her child, with the father also present if desired,and (4) the option of using spinal opioids for postoperative pain relief. The choicebetween spinal and epidural anesthesia is often based on physician preferences.Epidural anesthesia is preferred over spinal anesthesia by some clinicians becauseof the more gradual decrease in blood pressure associated with epidural anesthesia.Continuous epidural anesthesia also allows better control over the sensory level.Conversely, spinal anesthesia is easier to perform, has a more rapid, predictableonset, may produce a more intense (complete) block, and does not have thepotential for serious systemic drug toxicity (because of the smaller dose of localanesthetic employed). Regardless of the regional technique chosen, the ability toadminister a general anesthetic at any time during the procedure is mandatory.Moreover, administration of a nonparticulate antacid 1 h prior to surgery shouldalso be considered. General anesthesia offers (1) a very rapid and reliable onset, (2) control overthe airway and ventilation, and (3) potentially less hypotension than regionalanesthesia. General anesthesia also facilitates management in the event of severehemorrhagic complications such as placenta accreta. Its principal disadvantages arethe risk of pulmonary aspiration, the potential inability to intubate or ventilate thepatient, and drug-induced fetal depression. Present anesthetic techniques, however,limit the dose of intravenous agents such that fetal depression is usually notclinically significant with general anesthesia when delivery occurs within 10 minof induction of anesthesia. Regardless of the type of anesthesia, neonates deliveredmore than 3 min after uterine incision have lower Apgar scores and acidotic bloodgases.Regional AnesthesiaCesarean section requires a T4 sensory level. Because of the associated highsympathetic blockade, all patients should receive a 1000- to 1500-mL bolus oflactated Ringers injection prior to neural blockade. Crystalloid boluses do notconsistently prevent hypotension but can be helpful in some patients. Smallervolumes (250–500 mL) of colloid solutions, such as albumin or hetastarch, aremore effective. After injection of the anesthetic, the patient is placed supine withleft uterine displacement; supplemental oxygen (40–50%) is given; blood pressureis measured every 1–2 min until it stabilizes. Intravenous ephedrine, 10 mg, shouldbe used to maintain systolic blood pressure > 100 mm Hg. Small intravenous doses
  33. 33. of phenylephrine, 25–100 mkg, or an infusion up to 100 mkg/min may also be usedsafely. Some studies suggest less neonatal acidosis with phenylephrine comparedto ephedrine. Prophylactic administration of ephedrine (5 mg intravenous or 25 mgintramuscular) has been advocated by some clinicians for spinal anesthesia, asprecipitous hypotension may be seen but is not recommended for most patientsbecause of a risk of inducing excessive hypertension. Hypotension followingepidural anesthesia typically has a slower onset. Slight Trendelenburg positioningfacilitates achieving a T4 sensory level and may also help prevent severehypotension. Extreme degrees of Trendelenburg may interfere with pulmonary gasexchange.CSE Anesthesia The technique for CSE is described in the above section on combined spinalepidural analgesia. For cesarean section, it combines the benefit of rapid, reliable,intense blockade of spinal anesthesia with the flexibility of an epidural catheter.The catheter also allows supplementation of anesthesia and can be used forpostoperative analgesia. As mentioned previously, drugs given epidurally shouldbe administered and titrated carefully because the dural hole created by the spinalneedle increases the flux of epidural drugs into CSF and enhances their effects.General Anesthesia Pulmonary aspiration of gastric contents (incidence: 1:500–400 for obstetricpatients versus 1:2000 for all patients) and failed endotracheal intubation(incidence: 1:300 versus 1:2000 for all patients) during general anesthesia are themajor causes of maternal morbidity and mortality. Every effort should be made toensure optimal conditions prior to the start of anesthesia and to follow measuresaimed at preventing these complications. All patients should possibly receive prophylaxis against severenonparticulate aspiration pneumonia with 30 mL of 0.3 M sodium citrate 30–45min prior to induction. Patients with additional risk factors predisposing them toaspiration should also receive intravenous ranitidine, 50 mg, and/ormetoclopramide, 10 mg, 1–2 h prior to induction; such factors include morbidobesity, symptoms of gastroesophageal reflux, a potentially difficult airway, oremergent surgical delivery without an elective fasting period. Premedication withoral omeprazole, 40 mg, at night and in the morning also appears to be highlyeffective in high-risk patients undergoing elective cesarean section. Althoughanticholinergics theoretically may reduce lower esophageal sphincter tone,premedication with a small dose of glycopyrrolate (0.1 mg) helps reduce airwaysecretions and should be considered in patients with a potentially difficult airway. Pediatric Anesthesia
  34. 34. Pediatric patients are not small adults. Neonates (0–1 months), infants (1–12months), toddlers (1–3 years), and small children (4–12 years of age) havediffering anesthetic requirements. Safe anesthetic management depends on fullappreciation of the physiological, anatomic, and pharmacological characteristics ofeach group. These characteristics, which differentiate them from each other andadults, necessitate modification of anesthetic equipment and techniques. Indeedinfants are at much greater risk of anesthetic morbidity and mortality than are olderchildren; risk is generally inversely proportional to age, neonates being at highestrisk. In addition, pediatric patients are prone to illnesses that require uniquesurgical and anesthetic strategies.Pharmacological Differences Pediatric drug dosing is typically based on a per-kilogramrecommendation.Weight, however, does not take into account thedisproportionately larger pediatric intravascular and extracellular fluidcompartments, the immaturity of hepatic biotransformation pathways, increasedorgan blood flow, decreased protein binding, or higher metabolic rate. Thesevariables must be considered on an individual basis. Neonates and infants have a proportionately higher total water content (70–75%) than adults (50–60%). Total body water content decreases as fat and musclecontent increase with age. As a direct result, the volume of distribution for mostintravenous drugs is disproportionately higher in neonates, infants, and youngchildren, and the dose (per kilogram) is usually higher than in older children andadults. A disproportionately smaller muscle mass in neonates prolongs the clinicaltermination of action by redistribution to muscle for drugs such as thiopental andfentanyl. Neonates also have a relatively lower glomerular filtration rate andhepatic blood flow, as well as immature renal tubular function and immaturehepatic enzyme systems. Increased intraabdominal pressure and abdominal surgeryfurther reduce hepatic blood flow. All these factors impair renal drug handling,hepatic metabolism, or biliary excretion of many drugs in neonates and younginfants. Neonates also have decreased or impaired protein binding for some drugs,most notably thiopental, bupivacaine, and many antibiotics. In the first instance,increased free drug enhances potency and reduces the induction dose compared toolder children. In the second instance, an increase in free bupivacaine may enhancesystemic toxicity.Inhalational Anesthetics Neonates, infants, and young children have relatively higher alveolarventilation and lower FRC compared with older children and adults. This higherminute ventilation-to-FRC ratio with relatively higher blood flow to vessel-richorgans contributes to a rapid rise in alveolar anesthetic concentration and speedsinhalation induction. Furthermore, the blood/gas coefficients of volatile anesthetics
  35. 35. are lower in neonates than in adults, resulting in even faster induction times andpotentially increasing the risk of overdosing. The minimum alveolar concentration (MAC) for halogenated agents ishigher in infants than in neonates and adults. Unlike other agents, sevoflurane hasthe same MAC in neonates and infants. For unknown reasons, use of nitrous oxidein children does not augment the effects (lower MAC requirements) of desfluraneand to some extent sevoflurane as it does for other The blood pressure of neonates and infants tends to be more sensitive tovolatile anesthetics, probably because of not fully developed compensatorymechanisms (eg, vasoconstriction, tachycardia) and an immature myocardium thatis very sensitive to myocardial depressants. As with adults, halothane alsosensitizes the heart to catecholamines; the maximum recommended dose ofepinephrine in local anesthetic solutions during halothane anesthesia is 10 mkg/kg.Cardiovascular depression, bradycardia, and arrhythmias are significantly less withsevoflurane than with halothane. Halothane and sevoflurane are least likely toirritate the airway and cause breath holding or laryngospasm during. Volatileanesthetics appear to depress ventilation more in infants than in older children.Sevoflurane is associated with the least respiratory depression. Prepubertalchildren are at much less risk for halothane-induced hepatic dysfunction than areadults. There are no reported instances of renal toxicity from inorganic fluorideproduction during sevoflurane anesthesia in children. Overall, sevoflurane appearsto have a greater therapeutic index than halothane and has become a preferredinduction agent in pediatric anesthesia. The rate of emergence is fastest following desflurane and sevofluraneanesthesia, but both agents are associated with an increased incidence of agitationor delirium upon emergence, particularly in young children. Because of the latter,many clinicians switch to either isoflurane or halothane for maintenance anesthesiafollowing a sevoflurane induction. The speed of emergence from halothane andisoflurane anesthesia appears to be similar for procedures lasting less than 1 h.Nonvolatile Anesthetics Based on weight, infants and young children require larger doses of propofolbecause of a larger volume of distribution compared to adults. Children also have ashorter elimination half-life and higher plasma clearance for propofol. Whereasrecovery from a single bolus is not appreciably different from adults, recoveryfollowing a continuous infusion may be more rapid. For the same reasons, childrenmay require higher rates of infusion for maintenance of anesthesia (up to 250 mkg/kg/min). Propofol is not recommended for sedation of critically ill pediatricpatients in the intensive care unit (ICU). The drug has been associated with highermortality compared to other agents, and a controversial "propofol infusionsyndrome" has been described. Its essential features are metabolic acidosis,