Anatomy of BrainThe Brain is an important organ thatcontrol thought, memory, emotion,touch, motor skills, vision, respiration,temperature, hunger and every processthat regulate our body.The Brain can be divided into two partsby the tentorium cerebeli –1.) Supratentorial Compartment2.) Infratentorial Compartment
SUPRATENTORIAL COMPARTMENTS --It is the largest part of the brain.-It is divided by falx cerebri and iscontributed to by the anterior cranialfossa and middle cranial fossa.-The major content of this compartmentis cerebrum.-- Cerebrum is composed of right andleft hemispheres with each having afrontal, temporal, Parietal and occipitallobes.
Function of Cerebrum –Initiation of movement, coordination ofmovement, temperature, touch, vision,hearing, judgment, emotions, reasoning,problem solving and learning.The supratentorial compartmentcommunicates with the infratentorialcompartments via the opening oftentorial incisura.
Infratentorial Compartments-It includes –--Brain stem--CerebellumBrain Stem- It includes the mid brain, thepons and the medulla. Function of this area includes--Movement of the eyes and mouth.-Relaying sensory messages- hot, pain,loud.-Hunger, respiration, consciousness,Cardiac function, body temperature,involuntary muscle movement, Sneezing,coughing, vomiting and swallowing.
Cerebellum- Located at the back ofthe head.Its function include--Coordinate voluntary musclemovement and to maintain posture,balance and equilibrium.
Mass of abnormal tissue growing in anypart of the brain.The cause of brain tumor –-unknownOnly unequivocal risk factor for glial andmeningeal neoplasms is ionizing radiation.Alledged to increase the risk of braintumors -Use of cellular telephones -Exposure to high-tension wires -Use of hair dyes -Head trauma -Dietary exposure to n - nitrosurea compounds
Tumors can be divided into two types–1.) Primary – Most of the tumor areprimary (85%).2.) Secondary – 15%. Metastasis mostoften lungs or breasts.- Also malignant Melanoma,Hypernephroma or CA colon.
Brain tumor in Children’s :--In children brain tumors are thesecond most common tumor afterLeukaemia.Common tumors –Medulloblastoma, Gliomas,Astrocytomas, Ependymoma and Germcell tumor.
Sign & SymptomsIncreased intracranial pressure is themost likely explanation for s/s causedby brain tumors. Symptoms ofincreased ICP -Headache -n/v -Mental changes -Disturbances of consciousness
Perioperative Goals -Keep ICP within normal range -Recognize that autoregulation of CBF may be impaired -Hemodynamically stable induction and maintenance of anesthesia -Minimal brain swelling to optimize surgical exposure -Rapid return to a LOC that permits neurologic assessment
-Mean should remain below 15mm/hg-Events that can initiate abrupt increasesin ICP -Anxiety -Painful stimuli -Induction of anesthesia -Avoid noxious stimuli -Support ventilation to avoidhypercarbia secondary to drug-induceddepression of ventilation -Establish depth of anesthesia sufficientto blunt pressor responses tolaryngoscopy and tracheal intubation
Posture -Elevating the patients head to about 30 degrees above heart level encourages venous outflow from the brain and lowers ICP. -Avoid -Head down position -Extreme flexion or rotation of the patients headHyperventilation -Effectively and rapidly lowers the ICP
-CSF drainage -Draining CSF from the lateral cerebral ventricles or the lumbar subarachnoidspace decreases the intracranial volume and ICP-Hyperosmotic drugs -Mannitol -Draws water from tissues including the brain -Must replace some of the intravascular water lost through the kidneys -Administered in doses of 0.25 to 1.0 mg/kg over 15-30minutes. -Results in removal of about 100ml of water from the patient’s brain
Diuretics Furosemide -Useful if increased vascular fluid volume and plumonary edema -1mg/kg, may be more effective than mannitol -Does not introduce the risk of altered plasma osmolarityCorticosteroids Dexamethasone and methylprednisolone -Effective in lowering increased ICP caused by the development of localized cerebral edema around brain tumors.
Barbiturates -High doses effective for treating high ICP that develops after an acute head injury -Useful when other, more traditional methods of treatment have failed.
-Majority of intracranial Neurosurgicalprocedure are performed for asupratentorial mass lesion.-Supratentorial procedure includesthose for tumor, hematoma or Trauma.-Although the underline Pathology maydifferent for different lesion but theanaesthetic consideration are the same.
1.) Complete Medical History-Mainly for function of the heart and thelungs. Most perioperative morbidity andmortality results from poor Cardiac orPulmonary function.History of CNS Disorders – Seizuredisorders need to be assessed for typeand for adequacy of therapy.-Cerebral haemorrhage or prior strokesare noted.- Any residual speech, sensory or motordysfunction are recorded.
-Obtain the results of any recentintracranial or diagnostic procedureand consider possibility of residualpneumocephalus.2.) Review the patient list ofMedicationsi.) – Steroid increase serum glucoselevels by stimulating gluconeogenesisand direct cause adrenal suppressionthat may lead to hypotension withSurgical Stress.
ii.) –Mannitol and other diureties-reduce cerebral edema can lead tohypovolemia and electrolyte imbalance.- These can cause profoundhypotension upon anaestheticinduction and cardiac arrhythmiasiii.) Anti Hypertensive – Alter thepatients intravascular volume status.iv.) Tricyclic Antidepressant andL- Dopa – inducing intraoperative HTand cardiac arrhythmias.
v.) Benzodiazepines, phenothiazinesand butyrophenones –Cause perioperative hypotension andcloud the sensorium.3.) Physical Examination --Airway-Lungs and cardio vascular system.-Sign of hypovolemia – common findingin Neurosurgical patients because theyare often somnolent and haveinadequate oral intake.-They may also have increased urinarywater loss resulting from x-ray dye ordiuretics.
-Mild to moderate hypovolemiausually well tolerated but significanthypovolemia should be correctedbefore the induction of anaesthesia.4.) Neurological Examination –-Level of consciousness-Document any focal motor orsensory deficit.- Examination of sign and symptomof increased ICP.
5.) Laboratory Test-CBC-Blood ChemistryHyperventilation and diuresis decreasethe serum potassium level sopotassium supplementation should becorrect early.-Serum glucose level above 200 mg/dl isnot acceptable and insulin therapyshould be start to lower serum glucoseto the normal range.
6.) Radiological Examination –-Provide essential information abouttumor size and location, cerebraledema and midline shift.-Although the anaesthesiologist isgenerally not expert for interpretingCT or MRI scan.
MONITORING-ECG, BP, Pulse oximeter-FiO2 monitor-Temperature Probe-EtCo2 – Monitor hyperventilation andET tube disconnections or kinks.-Urinary catheterization-ICP monitoring (routinely not used)
MONITORING If the risk of venous air embolism is increased consider Central venous catheter or Pulmonary artery catheter Doppler transducer
PATIENT POSITION Supine with head elevated 15-30 degrees Useful for craniotomy to remove a supratentorial tumor Avoid excessive flexion or rotation of the head Can impair jugular vein patency
SITTING POSITION Advantages Disadvantages Excellent Decrease in BP surgical and cardiac exposure output Facilitation of Potential hazard cerebral venous of venous air and CSF embolism drainage
VENOUS AIR EMBOLISM Patients undergoing intracranial surgery are at increased risk Operative site is usually above the level of the patient’s heart Veins in the skull may not collapse
VENOUS AIR EMBOLISM Earlydetection is important for successful treatment Doppler transducer placed over the right heart Most sensitive indicator of intracardiac air Does not provide information as to volume of air TEE Sudden decrease in PCO2 may reflect increased deadspace
VENOUS AIR EMBOLISM Late signs Hypotension Tachycardia Cardiac dysrhythmias Cyanosis Mill wheel murmur
VENOUS AIR EMBOLISM Treatment Irrigate operative site Apply occlusive material Aspiration of air through right atrial catheter Discontinue nitrous oxide Apply PEEP May require sympathomimetic drugs B-agonists if marked decreases in cardiac output hyperbaric chamber if transfer can be accomplished within 8 hours
-Use drugs that produce rapid andreliable onset of unconsciousnesswith minimal effects on CBF -Thiopental, etomidate, propofol-Use NDMR, in large doses -3 times the median effective dose to facilitate intubation-Succ associated with transientincreases in ICP
Induction - can be performed byvarious agent. The best inductionagent is Barbiturates because itsadministration provides a profoundreduction in CMRO2 , CBF and ICP.-Smooth and gentle induction ofgeneral anaesthesia is moreimportant. An acceptable inductionsequence combines four steps –-1.) Preoxygenation and selfhyperventilation
2.) Thiopentone 3-4 mg/kg IV followedby mask ventilation to assure airwaypatency.3.) Vecuronium 0.1 mg/kg IV and maskhyperventilation with oxygen and N2O(50:50) until neuromuscular blockadeachieved.If there is C/I to use of N2O, at a smallconcentration of isoflurane to the O2.4.) Lidocaine 1.5 mg/kg IV andadditional thiopentone 2 mg/kg IV justbefore ET Intubation.
Rapid Sequence Induction - canbe performed with the samecombination of drugs as a routineinduction. However, cricoids pressureis applied, mask ventilation is notdelivered.-Vecuronium 0.15 mg/kg used forintubation.- In a patient with full stomach and adifficult airway, awake intubationshould be performed.
-Heavy topical anaesthesia and minimalIV sedation with subsequent oralendrotracheal intubation using alighted stylet is extremely effective inthese patient.If Narcotics are to be used as a part ofanaesthetic administer slowly duringinduction. Fentanyl or sufentanil makeinduction and ET intubation verysmooth.
Regarding the use of Narcotics-1.) Neurosurgical Patients may have arapid clouding of their sensorium withany sedative agent, hence theirprotective airway reflexes may beblunted quickly.2.) Narcotics induce hypoventilationwhich can be very dangerous in thesepatients.3.) The combination of Thiopentoneand Narcotics can produce dramaticdecrease in BP, hence the dose ofThiopentone must be reduced.
-Esmolol or Labetalol may also begiven prior to intubation. These drugblunt the hypertensive response tointubation.The dose of Thiopentone must beadjusted if these drugs areadministered.
Maintenance of Anaesthesia –It can be accomplished in a number ofways.These technique generally fall in to twocategories –1.) Primarily Volatile agent and2.) NarcoticsEither technique can be used.In Narcotics based anaesthetictechnique with either N2O or low dose (<1%) isoflurane in O2 is optimum.Fentanyl or sufentanil may be used.
Fentanyl 5µg/kg combined with < 1%isoflurane in O2 is an acceptabletechnique for anaesthetic maintenance.Alternatively, sufentanil 0.5 to 1 µg/kgloading dose, followed by eitherincremental bolus (not to be exceed 0.5µg/kg/hr) or IV infusion of 0.25 to 0.5µg/kg/hr in combination with < 1%isoflurane in O2 may be used.The sufentanil must be discontinuedapproximately 1 hr before the end ofsurgery.
If the patient has HT or tachycardianear the end of surgery, it is best totreat with either Labetalol or Esmolol.-A volatile agent preferably isofluranewith little or no narcoticsupplementation can also be used.- Hyperventilation combination with <1% isoflurane generally results instable intracranial dynamics.
N2O may be used in anaestheticregimen but it is contraindicated if thepatient is suspected to havepneumocephalus (recent intracranialsurgery or trauma) or if there ispotential for air embolism N2O expandboth the pneumocephalus and the airembolus. A large air embolus cancause cardiovascular collapse.-Hyperventilation during surgery wouldyield an arterial PCo2 of 25 to 30mmHg.
- If increase ICP is a problem, it may bebeneficial to reduce the PCo2 to 20 to 25mmHg.-Muscle relaxation is also importantduring neurosurgery relaxation preventpatient movement at inappropriatetime it may decrease ICP by relaxing thechest wall with decrease intrathoracicpressure and encourage venousdrainage.
Fluid Management –-A balanced salt solution is the fluid ofchoice for neurosurgical procedures.The volume of fluid administeredshould be minimized during theinduction of anaesthesia and then keptas low as hemodynamic stability andurine output will allow.--Use no dextrose containing solution.-Maintain hematocrit at 30 to 35 %.
- Patients who present for tumorsurgery should be kept on the dry sideof normal. Excess fluid administered tothese patients may cause brain edemaat the sites of blood brain barrierdisruption. Thus a dry but stablepatient is optimum for tumor surgery.
Emergence from anaesthesia followingsupratentorial surgery should besmooth and gentle.-The majority of patient can beextubated.-A patient who was comatosepreoperatively or who has undergonesignificant surgical manipulation forremoval of a large centrally locatedtumor is not a candidate for earlyextubation.
Such patient should remain intubatedand be allowed to awaken slowly inthe ICU after a period of monitoringand continued ventilation.
Manual of NeuroAnaesthesiaScott L. Mears, M.D., and Richard j.Sperry, M.D.