5. Anesthetic Monitoring

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  • The original stages and planes of anesthesia were based on patient response to diethyl ether and were established during WWI by Dr. Arthur Guedel.
  • A patient in stage I anesthesia is difficult to handle so the anesthetist wants to get the patient through this stage as quickly as possible.
  • To prevent injury to the animal, the restrainer, or the anesthetist, the patient should be passed through this stage as quickly as possible. Patients premedicated and rapidly induced with an injectable anesthetic pass through stages I and II without showing clinical signs of having done so.
  • Patient will move and show increased heart rate, respiratory rate and depth, and blood pressure along with a response to painful stimuli if surgery is attempted at this level.
  • Patients at this level may have to be bagged or manually ventilated.
  • Patients at this level are in danger of cardiac and respiratory arrest.
  • Maintaining the optimum anesthetic depth requires frequent assessment of the patient with proper adjustments to the rate of anesthetic administration throughout the procedure. When in doubt, err on the side of caution and keep a patient at the least depth that will fulfill the objectives.
  • There are advantages and disadvantages to using physical and mechanical monitoring. The anesthetist should use what is most effective for patient safety and the clinical situation.
  • Table 5-2 lists minimum and maximum acceptable heart rates and typical heart rates for anesthetized patients.
  • Three types of A-V heart blocks: first degree, second degree, and third degree. First- and second-degree blocks can be seen in normal resting horses. First- and second-degree blocks are commonly seen after administration of alpha 2 -agonists or with high vagal tone, hyperkalemia, or cardiac disease. Third-degree block indicates a cardiac disease and is not commonly seen in anesthetized patients.
  • The SPCs in supraventricular tachycardia appear normal.
  • VPCs are early, like SPCs, but appear different than a normal QRS complex. Isolated VPCs are common in anesthetized animals.
  • Ventricular tachycardia is treated with lidocaine if it is severe.
  • If any of the factors is affected by drugs, disease, surgical stimulation, or hydration status the blood pressure will be altered. Hypotension is common during anesthesia because of the drugs used. The exception is dissociatives.
  • MAP <60 mm Hg in small animals and ruminants indicates decreased organ perfusion. MAP <70 mm Hg in horses indicates decreased organ perfusion.
  • By palpating the pulse strength prior to and during anesthesia, the anesthetist can detect a change in the pulse strength that may indicate a drop in blood pressure and therefore a drop in organ perfusion.
  • Because about 98% of the oxygen carried in blood is bound to hemoglobin, the PCV is an important determinant of oxygen available to tissues.
  • Room air is ~21% oxygen. Average normal hemoglobin is 15 g/d. When PaO 2 = <80 mm Hg the percent SO 2 begins to drop more rapidly.
  • Patients with subnormal PaO 2 or SaO 2 readings may require supplemental oxygen delivery, ventilation through bagging, or use of a ventilator.
  • Monitoring parameters and indicators provide the anesthetist with ventilation information.
  • Tachypnea must be differentiated from panting.
  • A respirometer is located between the expiratory hose of a circle breathing circuit and the anesthetic machine.
  • Dyspnea may be caused by a blocked airway, respiratory disease, pressure build-up in the breathing circuit, or hypoxemia.
  • A capnograph is noninvasive and continuous monitoring, which provides waveform information (a capnogram) as well as a numerical display.
  • Subtle waveform changes can be caused by high or low gas flow, type of breathing circuit used, amount of dead space, excess moisture in sampling line, or blockage or leak in the system.
  • Blood gas analysis is most commonly performed in large animal practices. Sample collection is difficult because the sample must be from an artery or possibly the lingual vein. Handling a sample is labor intense: it must be stored on ice and analyzed within 2 hours. Blood gas analyzers are not commonly found in veterinary practices; the sample may have to be taken to a local reference laboratory or a human hospital laboratory.
  • During anesthesia, the greatest body temperature loss occurs in the first 20 minutes.
  • Reflexes that are absent in medium anesthesia are also absent in deep or excessive anesthetic depth so they cannot be used as an indicator of anesthetic overdose.
  • 5. Anesthetic Monitoring

    1. 1. To keep the patient safe and to regulate anesthetic depth Anesthetic Monitoring Chapter 5
    2. 2. Monitoring Parameters <ul><li>Vital signs </li></ul><ul><ul><li>Homeostatic mechanism’s response to anesthesia </li></ul></ul><ul><ul><li>Heart rate </li></ul></ul><ul><ul><li>Heart rhythm </li></ul></ul><ul><ul><li>Respiratory rate and depth </li></ul></ul><ul><ul><li>Mucous membrane color </li></ul></ul><ul><ul><li>Capillary refill time </li></ul></ul><ul><ul><li>Pulse strength </li></ul></ul><ul><ul><li>Blood pressure </li></ul></ul><ul><ul><li>Body temperature </li></ul></ul><ul><li>Best indicator of patient wellbeing </li></ul>
    3. 3. Monitoring Parameters (Cont’d) <ul><li>Reflexes </li></ul><ul><ul><li>Involuntary response to stimulus </li></ul></ul><ul><ul><li>Palpebral, corneal, pedal, swallowing, laryngeal, and papillary light reflexes </li></ul></ul><ul><ul><li>Indicators of anesthetic depth </li></ul></ul><ul><li>Parameters offer predictable responses to anesthesia at various depths </li></ul><ul><li>May be affected by drugs, disease, or individual response variation </li></ul><ul><li>Monitor anesthetized patients as often as possible; continuously is ideal </li></ul>
    4. 4. Stages and Planes of Anesthesia <ul><li>Four stages (I, II, III, IV) </li></ul><ul><li>Stage III divided into four planes </li></ul><ul><li>From stage I through stage IV there is a progressive decrease in pain perception, motor coordination, consciousness, reflex responses, muscle tone, and cardiopulmonary function </li></ul>
    5. 5. Stage I <ul><li>Period of voluntary movement </li></ul><ul><li>Patient begins to lose consciousness </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>Fear, excitement, disorientation, struggling, urination, defecation </li></ul></ul><ul><ul><li>Increased heart rate and respiratory rate </li></ul></ul><ul><li>Stage ends with loss of ability to stand and recumbency </li></ul>
    6. 6. Stage II <ul><li>Period of involuntary movement; the “excitement stage” </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>Breathing irregular </li></ul></ul><ul><ul><li>Vocalization, struggling, paddling </li></ul></ul><ul><ul><li>Increased heart and respiratory rate, pupils dilated, muscle tone marked, reflexes present </li></ul></ul><ul><li>Actions are not under conscious control </li></ul><ul><li>Stage ends with muscle relaxation, decreased respiratory rate, and decreased reflex activity </li></ul>
    7. 7. Stage III <ul><li>Period of surgical anesthesia </li></ul><ul><li>Divided into four planes </li></ul><ul><li>Plane 1: not adequate for surgery: </li></ul><ul><ul><li>Regular respiratory pattern, no involuntary limb movements </li></ul></ul><ul><ul><li>Eyeballs start to rotate ventrally, pupils partially constricted, decreased pupillary light reflex </li></ul></ul><ul><ul><li>Endotracheal tube may be passed and connected to gas anesthetic machine </li></ul></ul><ul><ul><li>Other reflexes are still present but decreased response </li></ul></ul>
    8. 8. Stage III Plane 2 <ul><li>Suitable depth for most surgical procedures </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>Regular and shallow respiration with decreased rate </li></ul></ul><ul><ul><li>Blood pressure and heart rate mildly decreased </li></ul></ul><ul><ul><li>Relaxed muscle tone </li></ul></ul><ul><ul><li>Pedal and swallowing reflexes are absent </li></ul></ul><ul><ul><li>Ventromedial eye rotation </li></ul></ul>
    9. 9. Stage III Plane 2 (Cont’d) <ul><li>Surgical stimulation may produce: </li></ul><ul><ul><li>Mild increase in heart rate, blood pressure, or respiratory rate </li></ul></ul><ul><ul><li>Patient remains unconscious and immobile </li></ul></ul><ul><ul><li>Pupillary light response is sluggish; pupil size is moderate </li></ul></ul>
    10. 10. Stage III Plane 3 <ul><li>Deep anesthesia—excessive for most procedures </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>Low heart and respiratory rates, decreased tidal volume </li></ul></ul><ul><ul><li>Reduced pulse strength </li></ul></ul><ul><ul><li>Increased capillary refill time (CRT) </li></ul></ul><ul><ul><li>Poor to absent papillary light reflex; central eyeballs; moderately dilated pupils </li></ul></ul><ul><ul><li>Reflexes are totally absent; muscle tone is very relaxed </li></ul></ul>
    11. 11. Stage III Plane 4 <ul><li>Early anesthesia overdose </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>Abdominal breathing </li></ul></ul><ul><ul><li>Fully dilated pupils; dry eyes </li></ul></ul><ul><ul><li>All reflexes are absent </li></ul></ul><ul><ul><li>Marked depression of the cardiovascular system, pale mucous membranes, increased CRT </li></ul></ul><ul><ul><li>Flaccid muscle tone </li></ul></ul>
    12. 12. Stage IV <ul><li>Period of anesthetic overdose </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>Cessation of respiration </li></ul></ul><ul><ul><li>Circulatory collapse </li></ul></ul><ul><ul><li>Death </li></ul></ul><ul><li>Resuscitate immediately to save the patient </li></ul>
    13. 13. Stage III in 3 Planes <ul><li>Alternative classification </li></ul><ul><li>Plane 1: “light” surgical anesthesia </li></ul><ul><ul><li>Not suitable for surgery </li></ul></ul><ul><li>Plane 2: “medium” surgical anesthesia </li></ul><ul><ul><li>Optimum depth for most surgical procedures </li></ul></ul><ul><li>Plane 3: “deep” surgical anesthesia </li></ul><ul><ul><li>Excessive depth </li></ul></ul>
    14. 14. Objectives of Surgical Anesthesia <ul><li>Patient doesn’t move </li></ul><ul><li>Patient isn’t aware </li></ul><ul><li>Patient doesn’t feel pain </li></ul><ul><li>Patient has no memory of the procedure </li></ul>
    15. 15. Monitoring Patient Safety <ul><li>Assess vital signs </li></ul><ul><ul><li>Physical </li></ul></ul><ul><ul><ul><li>Touch, hearing, vision </li></ul></ul></ul><ul><ul><li>Mechanical instruments </li></ul></ul><ul><ul><ul><li>Electrocardiogram </li></ul></ul></ul><ul><ul><ul><li>Blood pressure monitor </li></ul></ul></ul><ul><ul><ul><li>Capnograph </li></ul></ul></ul><ul><ul><ul><li>Doppler blood flow monitor </li></ul></ul></ul><ul><ul><ul><li>Pulse oximeter </li></ul></ul></ul>
    16. 16. Monitoring Patient Safety (Cont’d) <ul><li>Vital signs groupings </li></ul><ul><ul><li>Circulation </li></ul></ul><ul><ul><ul><li>Heart rate and rhythm, pulse strength, CRT, mucous membrane color, blood pressure </li></ul></ul></ul><ul><ul><li>Oxygenation </li></ul></ul><ul><ul><ul><li>Mucous membrane color, CRT, hemoglobin saturation, inspired oxygen, arterial blood oxygen </li></ul></ul></ul><ul><ul><li>Ventilation </li></ul></ul><ul><ul><ul><li>Respiratory rate and depth, breath sounds, end-expired carbon dioxide levels, arterial carbon dioxide, blood pH </li></ul></ul></ul>
    17. 17. Indicators of Circulation <ul><li>To ensure adequate circulatory function </li></ul><ul><ul><li>“ Continuous awareness of heart rate and rhythm during anesthesia, along with gross assessment of peripheral perfusion (pulse quality, mm color and CRT) are mandatory. Arterial blood pressure and ECG should also be monitored. There may be some situations where these may be temporarily impractical, e.g., movement of an anesthetized patient to a different area of the hospital.” ACVA Guidelines 2009 </li></ul></ul>
    18. 18. Indicators of Circulation: Heart Rate <ul><li>Physical assessment </li></ul><ul><ul><li>Palpation of apical pulse through the thoracic wall </li></ul></ul><ul><ul><li>Palpation of the peripheral pulse </li></ul></ul><ul><ul><li>Auscultation with stethoscope: more difficult in recumbent, anesthetized animals </li></ul></ul><ul><li>Mechanical assessment </li></ul><ul><ul><li>ECG machine </li></ul></ul><ul><ul><li>Blood pressure monitor </li></ul></ul><ul><ul><ul><li>Doppler blood flow detector or oscillometric monitor </li></ul></ul></ul><ul><ul><li>Intraarterial line and transducer </li></ul></ul>
    19. 19. Indicators of Circulation: Heart Rate (Cont’d) <ul><li>Bradycardia </li></ul><ul><ul><li>Depressant effect of most anesthetics </li></ul></ul><ul><ul><li>Alpha 2 -agonists and opioids </li></ul></ul><ul><ul><li>Excessive anesthesia depth </li></ul></ul><ul><ul><li>Adverse effects of drugs </li></ul></ul>
    20. 20. Indicators of Circulation: Heart Rate (Cont’d) <ul><li>Tachycardia </li></ul><ul><ul><li>Anticholinergics and cyclohexamines </li></ul></ul><ul><ul><li>Inadequate anesthetic depth </li></ul></ul><ul><ul><li>Pain </li></ul></ul><ul><ul><li>Hypotension </li></ul></ul><ul><ul><li>Blood loss and shock </li></ul></ul><ul><ul><li>Hypoxemia and hypercapnea </li></ul></ul>
    21. 21. Indicators of Circulation: Heart Rhythm <ul><li>Assessed along with heart rate </li></ul><ul><li>Normal sinus rhythm vs. sinus arrhythmia </li></ul><ul><ul><li>Both can be seen in anesthetized animals </li></ul></ul><ul><li>First- or second-degree heart block </li></ul><ul><ul><li>Use ECG to detect </li></ul></ul><ul><li>Causes of arrhythmias </li></ul><ul><ul><li>Drugs </li></ul></ul><ul><ul><ul><li>Anticholinergics, alpha 2- agonists, barbiturates, cyclohexamines </li></ul></ul></ul><ul><ul><li>Medical states or diseases </li></ul></ul><ul><ul><ul><li>Hypoxia, hypercarbia, heart disease, trauma, gastric dilatation-volvulus </li></ul></ul></ul>
    22. 22. Instruments Used to Monitor Heart Rate and Rhythm <ul><li>Esophageal stethoscope </li></ul><ul><ul><li>Thin flexible catheter attached to audio monitor or conventional stethoscope </li></ul></ul><ul><ul><li>Electronically amplifies heart sounds </li></ul></ul><ul><ul><li>Inserted into esophagus to level of the fifth rib and adjusted for maximum sound </li></ul></ul><ul><li>Electrocardiography </li></ul><ul><ul><li>A graphic representation of the electrical activity of the heart </li></ul></ul><ul><ul><li>Used to detect arrhythmias, which are common in anesthetized animals </li></ul></ul><ul><ul><li>Differentiate normal from abnormal and dangerous from harmless rhythms </li></ul></ul>
    23. 23. Esophageal Stethoscope
    24. 24. Cardiac Conduction System
    25. 25. ECG Pattern of Waveforms, Intervals, and Segments
    26. 26. Commonly Encountered Cardiac Arrhythmias <ul><li>Sinus arrhythmia (SA) </li></ul><ul><ul><li>Heart rate coordinated with respirations </li></ul></ul><ul><ul><li>Decreases during expiration </li></ul></ul><ul><ul><li>Increases during inspiration </li></ul></ul><ul><ul><li>Normal in dogs, horses, and cattle </li></ul></ul><ul><ul><li>Abnormal in cats </li></ul></ul>
    27. 27. Commonly Encountered Cardiac Arrhythmias (Cont’d) <ul><li>Sinus bradycardia </li></ul><ul><ul><li>Abnormally slow heart rate </li></ul></ul><ul><ul><li>Common during anesthesia: excessive anesthetic depth and drug reactions </li></ul></ul><ul><ul><li>Correct with reversal agents or anticholinergics </li></ul></ul><ul><li>Sinus tachycardia </li></ul><ul><ul><li>Abnormally fast heart rate </li></ul></ul><ul><ul><li>Inadequate anesthetic depth, drug reactions, surgical stimulation </li></ul></ul><ul><ul><li>Treat according to cause </li></ul></ul>
    28. 28. Sinus Arrhythmia
    29. 29. Commonly Encountered Cardiac Arrhythmias <ul><li>A-V heart block </li></ul><ul><ul><li>Delay or interruption of electrical impulse conduction through the A-V node </li></ul></ul><ul><li>First-degree A-V heart block </li></ul><ul><ul><li>Prolonged P-R interval </li></ul></ul><ul><li>Second-degree A-V heart block </li></ul><ul><ul><li>Occasional missing QRS complexes </li></ul></ul><ul><li>Third-degree A-V heart block </li></ul><ul><ul><li>Atrial and ventricular contractions occur independently </li></ul></ul><ul><ul><li>Randomly irregular P-R intervals </li></ul></ul>
    30. 30. First-, Second-, and Third-Degree A-V Heart Blocks
    31. 31. Commonly Encountered Cardiac Arrhythmias <ul><li>Premature complexes: complexes that occur too early </li></ul><ul><li>Supraventricular premature complexes (SPC) </li></ul><ul><ul><li>One or more normal QRS complexes closely following the previous QRS complex </li></ul></ul>
    32. 32. Supraventricular Tachycardia <ul><li>A series of three or more SPCs in a row </li></ul>
    33. 33. Ventricular Premature Complexes (VPC) <ul><li>One or more wide, bizarre QRS complexes closely following the previous QRS complex </li></ul>
    34. 34. Ventricular Tachycardia <ul><li>A series of three or more VPCs in a row </li></ul>
    35. 35. Fibrillation <ul><li>Chaotic, uncoordinated small muscle bundle contractions within the artria and ventricles </li></ul><ul><li>Atrial fibrillation </li></ul><ul><ul><li>Fine undulating baseline </li></ul></ul><ul><ul><li>Absence of P-waves </li></ul></ul><ul><ul><li>Tachycardia </li></ul></ul><ul><ul><li>Normal QRS complexes at irregular intervals </li></ul></ul>
    36. 36. Ventricular Fibrillation <ul><li>Undulating baseline </li></ul><ul><li>Absence of QRS complexes </li></ul>
    37. 37. Pulseless Electrical Activity (PEA) <ul><li>Cessation of heart contractions and/or palpable pulse in the presence of normal or nearly normal ECG </li></ul><ul><ul><li>Associated with cardiac arrest, the mechanical activity of the heart </li></ul></ul><ul><ul><li>ECG measures the electrical activity of the heart </li></ul></ul><ul><ul><li>Anesthetist must do both physical monitoring and ECG monitoring </li></ul></ul>
    38. 38. Indicators of Circulation: Capillary Refill Time (CRT) <ul><li>Rate of color return to oral mucous membrane after application of gentle digital pressure </li></ul><ul><ul><li>Indicates peripheral tissue blood perfusion </li></ul></ul><ul><ul><li>>2 seconds is prolonged and indicates poor perfusion </li></ul></ul><ul><ul><li>May result from epinephrine release, low blood pressure, hypothermia, cardiac failure, excessive anesthetic depth, blood loss, shock </li></ul></ul><ul><ul><li>Results in reduced temperature of affected part(s) </li></ul></ul>
    39. 39. Indicators of Circulation: Blood Pressure (BP) <ul><li>Force exerted by flowing blood on arterial walls </li></ul><ul><li>Evaluates tissue perfusion during anesthesia </li></ul><ul><li>Factors involved: </li></ul><ul><ul><li>Heart rate Stroke volume Vascular resistance </li></ul></ul><ul><ul><li>Arterial compliance (elasticity) Blood volume </li></ul></ul><ul><li>Varies throughout cardiac cycle </li></ul><ul><li>Hypotension vs. hypertension </li></ul>
    40. 40. Measuring Blood Pressure <ul><li>Systolic pressure </li></ul><ul><ul><li>Produced by contraction of the left ventricle </li></ul></ul><ul><ul><li>All BP monitoring instruments can measure systolic pressure </li></ul></ul><ul><li>Diastolic pressure </li></ul><ul><ul><li>Pressure that remains in the arteries when the heart is in the resting phase between contractions </li></ul></ul><ul><ul><li>Not all BP monitoring instruments can measure diastolic pressure </li></ul></ul>
    41. 41. Measuring Blood Pressure (Cont’d) <ul><li>Mean arterial pressure (MAP) </li></ul><ul><ul><li>Average pressure through the cardiac cycle </li></ul></ul><ul><ul><li>Best indicator of blood perfusion to internal organs </li></ul></ul><ul><ul><li>A mathematical calculation </li></ul></ul>
    42. 42. Indicators of Circulation: Pulse Strength <ul><li>Used as a rough indicator of blood pressure </li></ul><ul><li>Determined by the difference between systolic and diastolic blood pressure, vessel diameter, and other factors </li></ul><ul><li>Palpate the peripheral artery </li></ul><ul><ul><li>Lingual, dorsal pedal, femoral, carotid, facial, aural </li></ul></ul><ul><ul><li>Different arteries are appropriate for different species </li></ul></ul><ul><li>Lowered in anesthetized animals </li></ul><ul><li>A subjective interpretation </li></ul>
    43. 43. Blood Pressure Monitors <ul><li>Direct </li></ul><ul><ul><li>Reading obtained via indwelling catheter inserted into an artery (facial or aural) and attached to a pressure transducer and monitor </li></ul></ul><ul><ul><li>Most commonly used in equine practices and research facilities </li></ul></ul><ul><ul><li>Provides continuous reading throughout the cardiac cycle </li></ul></ul><ul><ul><li>Most accurate </li></ul></ul>
    44. 44. Blood Pressure Monitors (Cont’d) <ul><li>Indirect </li></ul><ul><ul><li>Reading is obtained by using an external sensor and cuff </li></ul></ul><ul><ul><li>Most commonly used in general veterinary practices </li></ul></ul><ul><ul><li>Noninvasive; cuff is placed over appropriate superficial artery </li></ul></ul><ul><ul><li>Doppler and oscillometric methods </li></ul></ul><ul><ul><li>Sphygmomanometer </li></ul></ul>
    45. 45. Central Venous Pressure <ul><li>Blood pressure in a large central vein (anterior vena cava) </li></ul><ul><ul><li>Assess blood return to the heart and heart function, especially right-sided heart failure </li></ul></ul><ul><li>A direct method of measurement </li></ul><ul><ul><li>Catheter from the jugular vein into the anterior vena cava </li></ul></ul><ul><ul><li>Connected to a water manometer </li></ul></ul><ul><ul><ul><li>>12-15 cm H 2 O considered elevated </li></ul></ul></ul><ul><li>Monitor trends over time rather than single readings </li></ul><ul><ul><li>May detect overhydration when administering IV fluids </li></ul></ul>
    46. 46. Indicators of Oxygenation <ul><li>To ensure adequate oxygenation of the patient’s arterial blood </li></ul><ul><ul><li>“Assessment of oxygenation should be done whenever possible by pulse oximetry, with blood gas analysis being employed when necessary for more critically ill patients.” ACVA Guidelines 2009 </li></ul></ul>
    47. 47. Indicators of Oxygenation: Mucous Membrane Color <ul><li>Assessed by observing the gingiva </li></ul><ul><ul><li>Varies from patient to patient </li></ul></ul><ul><ul><li>Evaluate prior to each procedure to determine baseline for patient </li></ul></ul><ul><li>Rough assessment of oxygenation and tissue perfusion </li></ul><ul><li>Alternate sites: tongue, conjunctiva of lower eyelid, mucous membrane lining of prepuce or vulva </li></ul>
    48. 48. Indicators of Oxygenation: Mucous Membrane Color (Cont’d) <ul><li>Pale mucous membranes: blood loss, anemia, poor capillary perfusion </li></ul><ul><li>Cyanotic membranes (blue to purple): respiratory arrest, oxygen deprivation, pulmonary disease </li></ul><ul><li>Affected by: body temperature, vascular resistance, gum disease </li></ul>
    49. 49. Physiology of Oxygen Transport <ul><li>Adequate oxygen necessary for metabolic processes </li></ul><ul><li>Components of total oxygen content </li></ul><ul><ul><li>Free, unbound oxygen molecules dissolved in plasma (minor content) </li></ul></ul><ul><ul><li>Oxygen chemically bound to hemoglobin in erythrocytes (four binding sites/hemoglobin molecule) </li></ul></ul><ul><li>Most oxygen is carried by hemoglobin </li></ul><ul><ul><li>100% saturation: all available hemoglobin binding sites are filled with oxygen </li></ul></ul>
    50. 50. Indicators of Oxygenation: Measuring Blood Oxygen <ul><li>Calculated oxygen content </li></ul><ul><ul><li>Measures both bound and dissolved oxygen </li></ul></ul><ul><ul><li>An accurate measurement expressed as mL/dL </li></ul></ul><ul><ul><li>(CaO 2 ) = (Hb × 1.39 × SaO 2 /100) + (PaO 2 × 0.003) </li></ul></ul><ul><li>Partial pressure (PaO 2 ) </li></ul><ul><ul><li>(N = 80-120 mm Hg arterial blood) </li></ul></ul><ul><ul><li>Measures unbound oxygen dissolved in plasma (N = ~1.5% total content) </li></ul></ul><ul><ul><li>Expressed as mm Hg and varies in arterial, capillary, or venous blood </li></ul></ul><ul><ul><li>Highest in arterial blood; lowest in venous blood </li></ul></ul>
    51. 51. Indicators of Oxygenation: Measuring Blood Oxygen (Cont’d) <ul><li>Percent oxygen saturation (percent SaO 2 ) </li></ul><ul><ul><li>Percentage of total number of available hemoglobin binding sites occupied by oxygen molecules (N =>97% total content) </li></ul></ul><ul><ul><li>Varies in arterial, capillary, or venous blood </li></ul></ul><ul><ul><li>Highest in arterial blood; lowest in venous blood </li></ul></ul>
    52. 52. Partial Pressure and Oxygen Saturation <ul><li>A nonlinear direct relationship </li></ul><ul><ul><li>As one decreases so does the other, but not at the same rate </li></ul></ul><ul><ul><li>As partial pressure decreases the oxygen saturation also decreases, but not as rapidly </li></ul></ul><ul><ul><li>Indicates oxygen availability in animals with normal hemoglobin levels </li></ul></ul>
    53. 53. Partial Pressure and Oxygen Saturation (Cont’d) <ul><li>Patient with low hemoglobin (one cause of anemia) </li></ul><ul><ul><li>Neither parameter gives an accurate indication of oxygen availability </li></ul></ul><ul><ul><li>Both parameters may be normal </li></ul></ul><ul><ul><li>Insufficient hemoglobin is available to carry all the oxygen necessary </li></ul></ul><ul><li>Patient is breathing pure oxygen from anesthetic machine </li></ul><ul><ul><li>Amount of dissolved oxygen will increase, not the percent saturation </li></ul></ul><ul><ul><li>Marginally affects the total oxygen content of blood </li></ul></ul>
    54. 54. Measuring Partial Pressure and Oxygen Saturation <ul><li>Blood gas analyzers measure partial pressure </li></ul><ul><li>Pulse oximeters measure oxygen saturation </li></ul><ul><li>PaO 2 and SaO 2 are elevated in anesthetized patients breathing pure oxygen </li></ul><ul><li>Low PaO 2 and SaO 2 observed during anesthesia can indicate hypoxemia and the need for oxygen supplementation or assisted ventilation </li></ul>
    55. 55. Pulse Oximeter <ul><li>Measures the saturation of hemoglobin and the heart rate </li></ul><ul><li>Red and infrared wavelength light technology with digital readout </li></ul><ul><ul><li>>95% saturation normal in patient breathing pure oxygen </li></ul></ul><ul><ul><li><90-95% saturation: patient is hypoxemic </li></ul></ul><ul><ul><li><90% saturation: therapy is required </li></ul></ul><ul><ul><li><85% saturation for >30 seconds: medical emergency </li></ul></ul><ul><li>Also used on nonanesthetized animals in intensive care </li></ul>
    56. 56. Pulse Oximeter Use <ul><li>Two types of probes: transmission or reflective </li></ul><ul><li>Transmission probes </li></ul><ul><ul><li>Clothes pin configuration </li></ul></ul><ul><ul><ul><li>One jaw light source, one jaw sensor </li></ul></ul></ul><ul><ul><li>Applied over nonpigmented tissue, relatively hairless and thin enough to transmit light </li></ul></ul><ul><ul><ul><li>Tongue, pinna, toe web, vulvar fold, prepuce, Achilles tendon, lip </li></ul></ul></ul><ul><ul><li>Light passes through the tissue and is measured by the sensor </li></ul></ul>
    57. 57. Pulse Oximeter Use (Cont’d) <ul><li>Reflective probes </li></ul><ul><ul><li>Light source and sensor are located next to each other </li></ul></ul><ul><ul><li>Placed in a hollow organ—esophagus or rectum </li></ul></ul><ul><ul><li>Light is reflected off tissue and is measured by the sensor </li></ul></ul>
    58. 58. Pulse Oximeter with Transmission Lingual Probe
    59. 59. Pulse Oximeter Probes and Placement Locations
    60. 60. Low Pulse Oximeter Readings <ul><li>Incorrect instrument use </li></ul><ul><li>Anesthetic agent causes vasoconstriction </li></ul><ul><li>Inadequate tissue perfusion </li></ul><ul><li>Inadequate oxygen delivery to patient </li></ul><ul><li>Inadequate ventilation </li></ul><ul><li>Inadequate circulation </li></ul>
    61. 61. Indicators of Ventilation <ul><li>To ensure that the patient’s ventilation is adequately maintained </li></ul><ul><ul><li>“Qualitative assessment of ventilation is essential as outlined for either (1) Observation of thoracic wall movement or observation of breathing bag movement when thoracic wall movement cannot be assessed. Or (2) Auscultation of breath sounds with an external stethoscope, an esophageal stethoscope, or an audible respiratory monitor; and capnography is recommended with blood gas analysis as necessary.” ACVA Guidelines 2009 </li></ul></ul>
    62. 62. Ventilation vs. Respiration <ul><li>Ventilation: movement of gas in and out of the alveoli </li></ul><ul><li>Respiration: processes by which oxygen is supplied to and used by the tissues and carbon dioxide is eliminated from the tissues </li></ul>
    63. 63. Indicators of Ventilation: Respiratory Rate (RR) <ul><li>Number of breaths per minute (bpm) </li></ul><ul><ul><li>Monitored visually by watching chest wall movements or movements of reservoir bag </li></ul></ul><ul><ul><li>Monitored mechanically with apnea monitor or capnograph </li></ul></ul><ul><ul><li>Normally decreases during anesthesia </li></ul></ul><ul><li>Tachypnea </li></ul><ul><ul><li>May be caused by hypercapnea, pulmonary disease, or mild surgical stimulus </li></ul></ul><ul><ul><li>May indicate a progression from moderate to light anesthesia during recovery </li></ul></ul>
    64. 64. Indicators of Ventilation: Tidal Volume (V T ) <ul><li>The amount of air inhaled during a breath </li></ul><ul><li>Monitored visually by watching chest wall movements or movements of reservoir bag </li></ul><ul><li>Monitored mechanically with respirometer </li></ul><ul><li>Hypoventilation </li></ul><ul><ul><li>Subnormal tidal volume or shallow breathing </li></ul></ul><ul><ul><li>Can lead to atelectasis </li></ul></ul><ul><ul><li>Reversed by gentle bagging </li></ul></ul><ul><li>Hyperventilation: elevated tidal volume </li></ul><ul><ul><li>Can result from hypercapnea or surgical stimulation </li></ul></ul>
    65. 65. Indicators of Ventilation: Respiratory Character <ul><li>The effort required to breathe </li></ul><ul><li>Monitored visually by watching the chest wall movements </li></ul><ul><ul><li>Measure time relationship between inspiration and expiration </li></ul></ul><ul><li>Monitor by auscultating the chest </li></ul><ul><ul><li>Listen for harsh noises, whistles, or squeaks </li></ul></ul><ul><li>Dyspnea: labored or difficult breathing </li></ul><ul><li>Apneustic respiratory pattern </li></ul><ul><ul><li>Prolonged pause between inspiration and expiration </li></ul></ul>
    66. 66. Apnea Monitor <ul><li>Monitors respirations </li></ul><ul><li>Warns anesthetist if patient hasn’t taken a breath in a preset time period </li></ul><ul><li>Detects temperature differences between inspired air (cool) and expired air (warm) </li></ul><ul><li>Sensor placed between endotracheal tube connector and breathing circuit </li></ul>
    67. 67. Apnea Monitor (Cont’d)
    68. 68. Indicators of Ventilation: Capnograph <ul><li>End-tidal carbon dioxide monitor (ETCO 2 ) </li></ul><ul><ul><li>Measures the carbon dioxide in air that is inhaled and exhaled </li></ul></ul><ul><ul><li>Value closely mirrors arterial CO 2 (PaCO 2 ) </li></ul></ul><ul><li>Mainstream capnograph: sensor placed directly between the endotracheal tube and breathing circuit </li></ul><ul><li>Sidestream capnograph: sensor located in a computerized monitor; air is pulled in through a tube attached to the fitting between the endotracheal tube and breathing circuit </li></ul>
    69. 69. Capnograph
    70. 70. Capnogram <ul><li>Waveform of carbon dioxide levels passing through the capnograph </li></ul><ul><ul><li>Normal shape is a modified rectangle </li></ul></ul><ul><li>Inspiration = CO 2 is 0 mm Hg </li></ul><ul><ul><li>Duration of 0 mm Hg reading is baseline </li></ul></ul><ul><li>Expiration = CO 2 is 35-45 mm Hg </li></ul><ul><ul><li>Increases slightly until end of expiratory effort </li></ul></ul><ul><ul><li>Abruptly returns to baseline at beginning of inspiration </li></ul></ul><ul><li>“ End-tidal” monitor </li></ul><ul><ul><li>CO 2 value at end of expiration most reflective of arterial CO 2 levels </li></ul></ul>
    71. 71. Capnogram (Cont’d)
    72. 72. Interpretation of a Capnogram <ul><li>Abnormal CO 2 levels are most commonly due to ventilation changes </li></ul><ul><li>Must evaluate </li></ul><ul><ul><li>Baseline value </li></ul></ul><ul><ul><li>ETCO 2 value </li></ul></ul><ul><ul><li>Waveform shape </li></ul></ul><ul><ul><li>Rate of change </li></ul></ul>
    73. 73. Capnogram Abnormalities Related to Ventilation or Equipment Problems <ul><li>Hyperventilation </li></ul><ul><ul><li>Gradual decrease in ETCO 2 value </li></ul></ul><ul><li>Hypoventilation </li></ul><ul><ul><li>Gradual increase in ETCO 2 value </li></ul></ul><ul><li>Flat line (No waveform) </li></ul><ul><ul><li>Lack of carbon dioxide reaching sensor or machine malfunction </li></ul></ul><ul><li>Elevated baseline </li></ul><ul><ul><li>Patient is rebreathing carbon dioxide or the sensor is contaminated </li></ul></ul><ul><li>Rounding of edges of waveform </li></ul><ul><ul><li>Leaking cuff or partially kinked endotracheal tube </li></ul></ul>
    74. 74. Capnogram Abnormalities Unrelated to Ventilation or Equipment Problems <ul><li>Cardiac arrest </li></ul><ul><ul><li>Rapid loss of waveform that returns if CPCR is successful </li></ul></ul><ul><li>Hypotension or sudden decrease in cardiac output </li></ul><ul><ul><li>Rapid decrease in height of rectangle </li></ul></ul><ul><li>Hypothermia </li></ul><ul><ul><li>Gradual decrease in ETCO 2 value (short rectangle) </li></ul></ul><ul><li>Hyperthermia </li></ul><ul><ul><li>Gradual increase in ETCO 2 value (tall rectangle) </li></ul></ul><ul><li>Subtle waveform changes </li></ul>
    75. 75. Indicators of Ventilation: Blood Gas Analysis <ul><li>Blood pH </li></ul><ul><li>Dissolved oxygen and carbon dioxide gas in arterial blood (PaO 2 and PaCO 2 ) or </li></ul><ul><li>Dissolved oxygen and carbon dioxide gas in venous blood (PvO 2 and PvCO 2 ) </li></ul><ul><li>Indicator of oxygenation, ventilation, acid-base status </li></ul><ul><li>Influenced by respiratory function </li></ul><ul><ul><li>Rate, depth, and character </li></ul></ul>
    76. 76. Carbon Dioxide Transport <ul><li>Bound to hemoglobin: 20-30% </li></ul><ul><li>Dissolved in plasma: 5-10% </li></ul><ul><li>Converted to bicarbonate and hydrogen ions by reaction with water: 60-70% </li></ul><ul><li>Evaluate patient CO 2 elimination by measuring PaCO 2 </li></ul><ul><ul><li>Normal PaCO 2 =<45 mm Hg in an awake patient </li></ul></ul><ul><ul><li>Often normally elevated during anesthesia: 45-60 mm Hg </li></ul></ul><ul><ul><li>Hypoventilation PaCO 2 =>60 mm Hg </li></ul></ul>
    77. 77. Carbon Dioxide Levels and Acid-Base Status <ul><li>Anesthetized patients may become mildly acidotic </li></ul><ul><ul><li>Higher CO 2 levels produce higher hydrogen ion concentration </li></ul></ul><ul><ul><li>Blood pH will be lower (7.20-7.30) </li></ul></ul><ul><li>Correct the underlying cause to correct the acidosis </li></ul><ul><ul><li>Compare blood pH and PaCO 2 levels to determine if acidosis is metabolic or respiratory </li></ul></ul>
    78. 78. PaO 2 <ul><li>Partial pressure of dissolved oxygen in arterial blood </li></ul><ul><ul><li>Should be five times the inspired oxygen concentration </li></ul></ul><ul><ul><li>Room air is ~21% oxygen so PaO 2 should be ~100 mm Hg </li></ul></ul><ul><ul><li>Pure oxygen is 100% oxygen so PaO 2 should be 500 mm Hg </li></ul></ul><ul><li>Hypoxemia in the absence of disease </li></ul><ul><ul><li>Rarely seen in anesthetized small animals or ruminants </li></ul></ul><ul><ul><li>Commonly seen in anesthetized horses </li></ul></ul>
    79. 79. Indicators of Body Temperature <ul><li>To ensure that patients do not encounter serious deviations from normal body temperature </li></ul><ul><ul><li>“Temperature should be measured periodically during anesthesia and recovery and if possible checked within a few hours after return to the wards.” ACVA Guidelines 2009 </li></ul></ul>
    80. 80. Indicators of Body Temperature: Core Body Temperature <ul><li>A vital sign regulated by thermoregulation </li></ul><ul><ul><li>Controlled by the hypothalamus </li></ul></ul><ul><ul><li>Shivering, metabolic rate, and peripheral blood flow keep temperature in the normal range </li></ul></ul><ul><ul><li>Is not an indicator of circulation, oxygenation, or ventilation </li></ul></ul><ul><li>Monitor every 15-30 minutes during anesthesia </li></ul><ul><ul><li>Rectal thermometer </li></ul></ul><ul><ul><li>Esophageal or rectal probe with monitor </li></ul></ul><ul><li>Anesthesia most often decreases body temperature </li></ul>
    81. 81. Body Temperature Loss During Anesthesia <ul><li>Influencing factors </li></ul><ul><ul><li>Shaving and skin preparation </li></ul></ul><ul><ul><li>Lack of shivering or muscular activities </li></ul></ul><ul><ul><li>Decreased metabolic rate </li></ul></ul><ul><ul><li>Opened body cavity and exposed viscera </li></ul></ul><ul><ul><li>Vasodilation caused by preanesthetic and anesthetic drugs </li></ul></ul><ul><ul><li>Age: pediatric and geriatric animals are more predisposed </li></ul></ul><ul><ul><li>Size: small patients lose heat faster </li></ul></ul><ul><ul><li>Temperature of IV fluids </li></ul></ul><ul><ul><li>Use of nonrebreathing systems </li></ul></ul>
    82. 82. Body Temperature Loss Complications During Anesthesia <ul><li>Prolonged anesthetic recovery </li></ul><ul><li>Reduced anesthetic dose to maintain surgical anesthesia </li></ul><ul><li>Predispose patient to anesthetic overdose </li></ul><ul><li>Shivering during recovery will increase oxygen demands </li></ul><ul><li>CNS depression and heart malfunction </li></ul>
    83. 83. Minimize or Manage Heat Loss During Anesthesia <ul><li>Avoid cold prep, surgery, and treatment rooms </li></ul><ul><li>Barrier between patient and table top </li></ul><ul><li>Warm IV fluids to ~100 ° C (37.5 ° F) </li></ul><ul><li>Circulating warm water blanket </li></ul><ul><li>Forced warm air blanket </li></ul><ul><li>Warm water bottles </li></ul><ul><li>Infrared heating lamps </li></ul><ul><li>Warmed fluids for abdominal cavity flush </li></ul><ul><li>Avoid heating pads </li></ul>
    84. 84. Hyperthermia During Anesthesia <ul><li>Influencing factors </li></ul><ul><ul><li>Excess external heat administration </li></ul></ul><ul><ul><li>Drug-induced reactions </li></ul></ul><ul><ul><li>Patient cannot dissipate heat </li></ul></ul><ul><li>Most often seen during or just before recovery </li></ul><ul><li>Management </li></ul><ul><ul><li>Cold fluids IV, IP, or rectally </li></ul></ul><ul><ul><li>Fans </li></ul></ul><ul><ul><li>Ice or alcohol application </li></ul></ul><ul><ul><li>Reversal agents </li></ul></ul><ul><ul><li>Increase flow rate of oxygen in nonrebreathing systems </li></ul></ul>
    85. 85. Malignant Hyperthermia <ul><li>Most commonly seen in pigs </li></ul><ul><li>Genetic defect </li></ul><ul><ul><li>Excess muscle metabolism when using some anesthetic drugs or muscle relaxants </li></ul></ul><ul><ul><li>Can be caused by restraint </li></ul></ul><ul><li>Clinical signs </li></ul><ul><ul><li>Patient becomes hot and stiff </li></ul></ul><ul><ul><li>Ears turn red </li></ul></ul><ul><ul><li>Increased carbon dioxide production </li></ul></ul><ul><ul><li>Tachyarrythmias </li></ul></ul>
    86. 86. Malignant Hyperthermia (Cont’d) <ul><li>Management </li></ul><ul><ul><li>Stop anesthesia immediately and administer 100% oxygen </li></ul></ul><ul><ul><li>Use cooling methods </li></ul></ul><ul><ul><li>Treat with dantrolene </li></ul></ul>
    87. 87. Assessment of Anesthetic Depth <ul><li>To make sure the patient is at a depth that provides immobility, unconsciousness, and lack of awareness of pain while avoiding conditions that endanger the patient such as hypoventilation, hypoxemia, hypotension, and hypothermia. </li></ul>
    88. 88. Assessment of Anesthetic Depth: Reflexes <ul><li>An unconscious response to a stimulus </li></ul><ul><ul><li>Conscious animals and protective reflexes </li></ul></ul><ul><ul><li>Decreased reflexes to stage III, plane 3 level anesthesia (when there are few to none) </li></ul></ul><ul><li>Reflexes evaluated </li></ul><ul><ul><li>Swallowing, laryngeal, pedal, palpebral, corneal, papillary light reflex </li></ul></ul><ul><li>Reported as present, decreased, or absent </li></ul>
    89. 89. Swallowing Reflex <ul><li>A normal response to food or saliva in the pharynx </li></ul><ul><li>Monitored by viewing the ventral neck region </li></ul><ul><li>Present in light surgical anesthesia </li></ul><ul><li>Lost in medium surgical anesthesia </li></ul><ul><li>Returns just before the patient regains consciousness </li></ul><ul><li>Used to determine when to pull the endotracheal tube </li></ul>
    90. 90. Laryngeal Reflex <ul><li>Epiglottis and vocal cords close immediately when larynx is touched by an object </li></ul><ul><li>Prevents tracheal aspiration </li></ul><ul><li>Observed during intubation if animal is in the light plane of anesthesia </li></ul><ul><li>Makes intubation difficult </li></ul><ul><ul><li>Especially in cats, pigs, and small ruminants </li></ul></ul><ul><li>May cause laryngospasm in cats, pigs, and small ruminants </li></ul>
    91. 91. Palpebral Reflex <ul><li>The blink reflex in response to a light tap on the medial or lateral canthus </li></ul><ul><li>May be elicited by lightly stroking the hairs of the upper eyelid </li></ul><ul><li>Present in light anesthesia </li></ul><ul><li>Often lost during medium anesthesia, although the exact point varies </li></ul><ul><li>Slow palpebral response in horses indicates adequate surgical anesthetic depth </li></ul><ul><li>Ruminants tend to have a slightly stronger reflex than horses </li></ul>
    92. 92. Palpebral Reflex (Cont’d)
    93. 93. Pedal Reflex <ul><li>Flexion or withdrawal of limb in response to squeezing, twisting, or pinching a digit or pad </li></ul><ul><li>Used in small animals only </li></ul><ul><li>Varies from subtle muscle contraction to full withdrawal of limb </li></ul><ul><li>Varies with depth of anesthesia </li></ul><ul><ul><li>Present in light anesthesia </li></ul></ul><ul><ul><li>Absent in medium anesthesia </li></ul></ul><ul><li>Requires a high intensity stimulus </li></ul>
    94. 94. Pedal Reflex (Cont’d)
    95. 95. Corneal Reflex <ul><li>Retraction of eyeball within orbit and/or a blink in response to corneal stimulation </li></ul><ul><li>Touch the cornea with a drop of sterile saline or artificial tears </li></ul><ul><li>Most useful in large animals; difficult to elicit in small animals </li></ul><ul><li>Present in light and medium anesthesia; absent in deep or excessive anesthesia </li></ul><ul><li>Used primarily to determine if a LA patient is too deep </li></ul>
    96. 96. Corneal Reflex (Cont’d)
    97. 97. Pupillary Light Reflex (PLR) <ul><li>Constriction of pupils in response to bright light shined on one retina </li></ul><ul><li>Present in light and medium anesthesia; absent in deep anesthesia </li></ul><ul><li>Dazzle reflex </li></ul><ul><ul><li>Blink response to bright light shined on retinas </li></ul></ul><ul><ul><li>Same significance as PLR </li></ul></ul><ul><ul><li>Lost very early in anesthesia </li></ul></ul>
    98. 98. Other Indicators of Anesthetic Depth <ul><li>Spontaneous movement </li></ul><ul><li>Muscle tone </li></ul><ul><li>Eye position </li></ul><ul><li>Pupil size </li></ul><ul><li>Nystagmus </li></ul><ul><li>Salivary and lacrimal secretions </li></ul><ul><li>Heart and respiratory rates </li></ul><ul><li>Response to surgical stimulation </li></ul>
    99. 99. Indicators of Anesthetic Depth
    100. 100. Indicators of Anesthetic Depth (Cont’d)
    101. 101. Judging Anesthetic Depth <ul><li>Monitor as many variables as possible </li></ul><ul><li>No one piece of information is reliable by itself </li></ul><ul><li>Each animal will respond in its own unique way to anesthesia </li></ul>
    102. 102. Recording Information During Anesthesia <ul><li>Objective: </li></ul><ul><ul><li>“To maintain a legal record of significant events related to the anesthetic period. </li></ul></ul><ul><ul><li>To enhance recognition of significant trends or unusual values for physiologic parameters and allow assessment of the response to intervention.” ACVA Guidelines 2009 </li></ul></ul>
    103. 103. Recording Information During Anesthesia (Cont’d) <ul><li>Recommendations: </li></ul><ul><ul><li>“Record all drugs administered to each patient in the peri-anesthetic period and in early recovery, noting the dose, time, and route of administration, as well as any adverse reaction to a drug or drug combination.” ACVA Guidelines 2009 </li></ul></ul>
    104. 104. Recording Information During Anesthesia (Cont’d) <ul><li>Recommendations: </li></ul><ul><ul><li>“Record monitored variables on a regular basis (minimum every 5 to 10 minutes) during anesthesia. The minimum variables that should be recorded are heart rate and respiratory rate, as well as oxygenation status and blood pressure if these were monitored.” ACVA Guidelines 2009 </li></ul></ul>
    105. 105. Recording Information During Anesthesia (Cont’d) <ul><li>Recommendations: </li></ul><ul><ul><li>“Record heart rate, respiratory rate, and temperature in the early recovery phase. Any untoward events or unusual circumstances should be recorded for legal reasons, and for reference should the patient require anesthesia in the future.” ACVA Guidelines 2009 </li></ul></ul>
    106. 106. Anesthesia Record
    107. 107. Completed Anesthetic Record

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