Anaesthesia for

Supratentorial Mass

By - Dr.Govind Sahai Bairwa

Under the guidance of

Dr. Tarun Lall

The Brain is an important organ that control thought, memory, emotion, touch, motor skills, vision, respiration, temperature, hunger and every process that regulate our body. The Brain can be divided into two parts by the tentorium cerebeli – 1.) Supratentorial Compartment2.) Infratentorial Compartment

Anatomy of Brain

SUPRATENTORIAL COMPARTMENTS -

-It is the largest part of the brain.-It is divided by falx cerebri and is contributed to by the anterior cranial fossa and middle cranial fossa.-The major content of this compartment is cerebrum.-- Cerebrum is composed of right and left hemispheres with each having a frontal, temporal, Parietal and occipital lobes.

Function of Cerebrum – Initiation of movement, coordination of movement, temperature, touch, vision, hearing, judgment, emotions, reasoning, problem solving and learning.The supratentorial compartment communicates with the infratentorial compartments via the opening of tentorial incisura.

Infratentorial Compartments-It includes – --Brain stem--Cerebellum

Brain Stem- It includes the mid brain, the pons 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 of the head.Its function include- -Coordinate voluntary muscle movement and to maintain posture, balance and equilibrium.

Mass of abnormal tissue growing in any part of the brain.The cause of brain tumor – -unknownOnly unequivocal risk factor for glial and meningeal neoplasms is ionizing radiation. Alledged to increase the risk of brain tumors

-Use of cellular telephones-Exposure to high-tension wires-Use of hair dyes-Head trauma-Dietary exposure to n - nitrosurea compounds

Intracranial Tumors

Tumors can be divided into two types – 1.) Primary – Most of the tumor are primary (85%).2.) Secondary – 15%. Metastasis most often lungs or breasts.- Also malignant Melanoma, Hypernephroma or CA colon.

Primary Tumors – 1.) Benign – Meningiomas, Pitutary Adenomas, Craniopharyngioma, Epidermoid cyst, Neurocytoma, Haemangioma, Pilocytic astrocytoma.2.) Malignant – Astrocytoma/Glioma, Ependymoma, Medulloblastoma, Lymphoma, Germ cell tumor.

Brain tumor in Children’s :--In children brain tumors are the second most common tumor after Leukaemia.Common tumors – Medulloblastoma, Gliomas, Astrocytomas, Ependymoma and Germ cell tumor.

Sign & SymptomsIncreased intracranial pressure is the most likely explanation for s/s caused by brain tumors. Symptoms of increased 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

Management of Anaesthesia

-Mean should remain below 15mm/hg -Events that can initiate abrupt increases in ICP

-Anxiety-Painful stimuli-Induction of anesthesia

-Avoid noxious stimuli -Support ventilation to avoid hypercarbia secondary to drug-induced depression of ventilation -Establish depth of anesthesia sufficient to blunt pressor responses to laryngoscopy and tracheal intubation

ICP

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 head

Hyperventilation-Effectively and rapidly lowers the ICP

Methods to DecreaseICP

-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

DiureticsFurosemide

-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 osmolarity

Corticosteroids 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 Neurosurgical procedure are performed for a supratentorial mass lesion.-Supratentorial procedure includes those for tumor, hematoma or Trauma.-Although the underline Pathology may different for different lesion but the anaesthetic consideration are the same.

1.) Complete Medical History-Mainly for function of the heart and the lungs. Most perioperative morbidity and mortality results from poor Cardiac or Pulmonary function.History of CNS Disorders – Seizure disorders need to be assessed for type and for adequacy of therapy. -Cerebral haemorrhage or prior strokes are noted.- Any residual speech, sensory or motor dysfunction are recorded.

Preoperative Evaluation

-Obtain the results of any recent intracranial or diagnostic procedure and consider possibility of residual pneumocephalus.2.) Review the patient list of Medicationsi.) – Steroid increase serum glucose levels by stimulating gluconeogenesis and direct cause adrenal suppression that may lead to hypotension with Surgical Stress.

ii.) –Mannitol and other diureties- reduce cerebral edema can lead to hypovolemia and electrolyte imbalance.- These can cause profound hypotension upon anaesthetic induction and cardiac arrhythmias iii.) Anti Hypertensive – Alter the patients intravascular volume status.iv.) Tricyclic Antidepressant and L- Dopa – inducing intraoperative HT and cardiac arrhythmias.

v.) Benzodiazepines, phenothiazines and butyrophenones – Cause perioperative hypotension and cloud the sensorium.

3.) Physical Examination - -Airway-Lungs and cardio vascular system.-Sign of hypovolemia – common finding in Neurosurgical patients because they are often somnolent and have inadequate oral intake.-They may also have increased urinary water loss resulting from x-ray dye or diuretics.

-Mild to moderate hypovolemia usually well tolerated but significant hypovolemia should be corrected before the induction of anaesthesia.4.) Neurological Examination – -Level of consciousness -Document any focal motor or sensory deficit.- Examination of sign and symptom of increased ICP.

5.) Laboratory Test-CBC-Blood ChemistryHyperventilation and diuresis decrease the serum potassium level so potassium supplementation should be correct early.-Serum glucose level above 200 mg/dl is not acceptable and insulin therapy should be start to lower serum glucose to the normal range.

6.) Radiological Examination – -Provide essential information about tumor size and location, cerebral edema and midline shift.-Although the anaesthesiologist is generally not expert for interpreting CT or MRI scan.

MONITORING-ECG, BP, Pulse oximeter -FiO2 monitor-Temperature Probe -EtCo2 – Monitor hyperventilation and ET tube disconnections or kinks. -Urinary catheterization -ICP monitoring (routinely not used)

MONITORING If the risk of venous air embolism

is increased considerCentral venous catheter orPulmonary artery catheterDoppler transducer

PATIENT POSITIONSupine with head elevated 15-30

degreesUseful for craniotomy to remove

a supratentorial tumorAvoid excessive flexion or

rotation of the headCan impair jugular vein patency

SITTING POSITIONAdvantages

Excellent surgical exposureFacilitation of cerebral venous

and CSF drainage

DisadvantagesDecrease in BP and cardiac

outputPotential hazard of venous air

embolism

VENOUS AIR EMBOLISMPatients undergoing intracranial

surgery are at increased riskOperative site is usually above

the level of the patient’s heartVeins in the skull may not

collapse

VENOUS AIR EMBOLISMEarly detection is important for

successful treatmentDoppler transducer placed over

the right heartMost sensitive indicator of intracardiac air

Does not provide information as to volume of air

TEESudden decrease in PCO2 may

reflect increased deadspace

VENOUS AIR EMBOLISMLate signs

HypotensionTachycardiaCardiac dysrhythmiasCyanosisMill wheel murmur

VENOUS AIR EMBOLISMTreatment

Irrigate operative siteApply occlusive materialAspiration of air through right

atrial catheterDiscontinue nitrous oxideApply PEEPMay require sympathomimetic

drugsB-agonists if marked decreases

in cardiac outputhyperbaric chamber if transfer

can be accomplished within 8 hours

-Use drugs that produce rapid and reliable onset of unconsciousness with minimal effects on CBF

-Thiopental, etomidate, propofol

-Use NDMR, in large doses-3 times the median effective dose to facilitate intubation

-Succ associated with transient increases in ICP

Induction

Induction - can be performed by various agent. The best induction agent is Barbiturates because its administration provides a profound reduction in CMRO2 , CBF and ICP.-Smooth and gentle induction of general anaesthesia is more important. An acceptable induction sequence combines four steps –-1.) Preoxygenation and self hyperventilation

2.) Thiopentone 3-4 mg/kg IV followed by mask ventilation to assure airway patency.3.) Vecuronium 0.1 mg/kg IV and mask hyperventilation with oxygen and N2O (50:50) until neuromuscular blockade achieved.If there is C/I to use of N2O, at a small concentration of isoflurane to the O2.4.) Lidocaine 1.5 mg/kg IV and additional thiopentone 2 mg/kg IV just before ET Intubation.

Rapid Sequence Induction - can be performed with the same combination of drugs as a routine induction. However, cricoids pressure is applied, mask ventilation is not delivered.-Vecuronium 0.15 mg/kg used for intubation.- In a patient with full stomach and a difficult airway, awake intubation should be performed.

-Heavy topical anaesthesia and minimal IV sedation with subsequent oral endrotracheal intubation using a lighted stylet is extremely effective in these patient. If Narcotics are to be used as a part of anaesthetic administer slowly during induction. Fentanyl or sufentanil make induction and ET intubation very smooth.

Regarding the use of Narcotics- 1.) Neurosurgical Patients may have a rapid clouding of their sensorium with any sedative agent, hence their protective airway reflexes may be blunted quickly.2.) Narcotics induce hypoventilation which can be very dangerous in these patients.3.) The combination of Thiopentone and Narcotics can produce dramatic decrease in BP, hence the dose of Thiopentone must be reduced.

-Esmolol or Labetalol may also be given prior to intubation. These drug blunt the hypertensive response to intubation. The dose of Thiopentone must be adjusted if these drugs are administered.

Maintenance of Anaesthesia – It can be accomplished in a number of ways.These technique generally fall in to two categories – 1.) Primarily Volatile agent and 2.) NarcoticsEither technique can be used.In Narcotics based anaesthetic technique 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 acceptable technique for anaesthetic maintenance.Alternatively, sufentanil 0.5 to 1 µg/kg loading dose, followed by either incremental bolus (not to be exceed 0.5 µg/kg/hr) or IV infusion of 0.25 to 0.5 µg/kg/hr in combination with < 1% isoflurane in O2 may be used.The sufentanil must be discontinued approximately 1 hr before the end of surgery.

If the patient has HT or tachycardia near the end of surgery, it is best to treat with either Labetalol or Esmolol.-A volatile agent preferably isoflurane with little or no narcotic supplementation can also be used.- Hyperventilation combination with < 1% isoflurane generally results in stable intracranial dynamics.

N2O may be used in anaesthetic regimen but it is contraindicated if the patient is suspected to have pneumocephalus (recent intracranial surgery or trauma) or if there is potential for air embolism N2O expand both the pneumocephalus and the air embolus. A large air embolus can cause cardiovascular collapse.-Hyperventilation during surgery would yield an arterial PCo2 of 25 to 30 mmHg.

- If increase ICP is a problem, it may be beneficial to reduce the PCo2 to 20 to 25 mmHg.-Muscle relaxation is also important during neurosurgery relaxation prevent patient movement at inappropriate time it may decrease ICP by relaxing the chest wall with decrease intrathoracic pressure and encourage venous drainage.

Fluid Management –-A balanced salt solution is the fluid of choice for neurosurgical procedures. The volume of fluid administered should be minimized during the induction of anaesthesia and then kept as low as hemodynamic stability and urine output will allow.--Use no dextrose containing solution.-Maintain hematocrit at 30 to 35 %.

- Patients who present for tumor surgery should be kept on the dry side of normal. Excess fluid administered to these patients may cause brain edema at the sites of blood brain barrier disruption. Thus a dry but stable patient is optimum for tumor surgery.

Emergence from anaesthesia following supratentorial surgery should be smooth and gentle. -The majority of patient can be extubated.-A patient who was comatose preoperatively or who has undergone significant surgical manipulation for removal of a large centrally located tumor is not a candidate for early extubation.

Such patient should remain intubated and be allowed to awaken slowly in the ICU after a period of monitoring and continued ventilation.

Manual of NeuroAnaesthesiaScott L. Mears, M.D., and Richard j. Sperry, M.D.

References

THANKS