Awake craniotomy has an edge over general anaesthesia

Dr Ratan Chelani and Dr E P Borges

Awake craniotomy is performed for resection of epileptogenic foci and other lesions (tumors and arteriovenous malformation), which are close to eloquent (important), ie motor and speech areas of the brain. Basic principle in keeping the patient awake during surgery is to prevent damage during surgery, to functionally important areas of the brain by performing cortical mapping, which requires patient to be awake to test his speech and to watch his movements.

By keeping the patient awake also minimises the interference of anaesthetic drugs on recordings of electrocorticography (ECOG), which is done to identify the epileptogenic foci in the brain. It presents a unique challenge for the attending anaesthesiologist to provide suitable conditions by keeping the patient calm and co-operative, without jeopardising his safe and comfortable intra-operative journey during awake craniotomy.

Successful procedure demands pre-operative assessment and proper selection of the patients, effective local anaesthetic (skull block) blockade and properly monitored sedation. Proper teamwork, patience and pleasant operating room (OT) atmosphere are the other prerequisites for awake craniotomy.

About 75 cases of awake craniotomy have been conducted at Hinduja Hospital in the past six years. First awake craniotomy was performed on 16th November, 1998 in a 32-year-old male patient. The youngest patient who had undergone awake craniotomy was a 9-year-old child in 2001, diagnosed as a case of left parietal astrocytoma.

Pre-operative Visit

It forms an important part of the procedure. After detailed history, the patient is assessed for psychological and mental status to undergo awake craniotomy. Patient is explained about the need to carry out surgery, while he is awake to establish a relationship of confidence and trust between the patient and the doctors operating on him.

Another important point not to be forgotten is to rule out the difficult airway to prevent last minute difficultry in incubating the patient. Mild sedative can be given at night before surgery to allay his anxiety.

Skull Block

It involves infiltration of the nerves supplying the scalp. Successful skull block helps in the application of head clamp pins and to raise the scalp flaps without causing any discomfort to the patient. Following nerves are to be blocked bilaterally during skull block:

1. Supraorbital and supratrochlear nerves (2 ml above eyebrow). 2. Auriculotemporal and zygomaticotemporal nerves (5 ml 1.5 anterior to tragus of ear). 3. Post auricular branches of greater auricular nerve (2 ml posterior to ear at tragus level). 4. Greater, lesser and third occipital nerves (5 ml along superior nuchal line halfway between occipital protuberance and mastoid process)

Bupivacaine and lignocaine combined with epinephrine can be used to carry out the block. Success of the surgery will greatly depend on adequate skull block otherwise patient becomes restless and uncooperative requiring higher doses of analgesics and sedatives which can interfere with cortical mapping and recordings of electrocorticography (ECoG).

Sedation

Awake craniotomy takes about three to five hours and some sedation is always required, as patient has to remain motionless in a particular position for such a long time. Sedation should be titrated in such a way that it does not interfere with the ECoG recordings and the patient remains alert and cooperative during cortical mapping and resection of the tumor.

Various drugs suggested for sedation either alone or in combination are:

1. Propofol (300-500 mgm/kg bolus and infusion 25-75mgm/kg/min)

2. Opioids:

• Fentanyl (0.7 mgm/kg and infusion 0.01 mg/kg/min).
• Sufentanil (0.075 mg/kg and infusion 0.0015 mg/kg/min).
• Alfentanil (7.5 mg/kg and infusion 0.5 mg/kg/min).

Additional supplemental in half the initial dose of the sedative can be given if required. Advantages of propofol include short acting drug, amnesic, antiemetic, reduced incidence of seizures, minimal effects on ECoG recordings and minimal effects on ventilation in low doses. Other drugs, which have been used, are midazolam, pentazocine and droperidol.

Other Intraoperative Considerations

Only one large peripheral intravenous cannula is inserted. Monitoring during awake craniotomy includes ECG, non-invasive blood pressure, pulse oxymetry and capnography. Central venous catheter and invasive arterial cannula are optional for the anaesthesiologist, but preferably should be avoided to minimise trauma to the patient.

Also the urinary catheter is routinely not inserted as it causes irritation to the patient and might become the cause for his restlessness. All patients are provided with supplemental oxygen through nasal prongs. Antibiotics, antiemetics and steroids are given at the start of surgery.

Patient can be positioned either in the supine or lateral position. Patient is more comfortable in the lateral position due to long surgery hours and it should be preferred over the supine position. Additional local anaesthetic is injected along the line of incision and in the dura leaflets. Brain being painless, sedatives can be switched off after the dura is opened and restarted during closure of wound. Soft pleasant music is welcome. Draping is done in such a way to maintain eye to eye contact with the patient. Constant communication is maintained with the patient and he should be made aware of the progress of the surgery.

ge Guidance System (Navigation):

Guides surgeon to capture 3-dimensional view of the underlying lesion, helping to locate the exact site of surgery. Various problems which can be encountered during awake craniotomy include

a) Nausea , vomiting (use antiemetics).

b) Patient getting restless and un-cooperative (give assurance or convert to general anaesthesia (GA).

c) Airway obstruction (nasopharyangeal airway).

d) Inadequate analgesia (give analgesics).

e) Convulsions ( managed with midazolam and /or propofol or convert to general anaesthesia (G A).

f) Full urinary bladder (catheterise).

g) Tight brain (hyperventilation, diuretics).

h) Fall in O2 saturation (reduce sedation, increase O2 concentration)

i) Attending anaesthesiologist should always be aware of these problems and act accordingly in such situations. One should keep the option of converting to GA if required during surgery.

Postoperatively patient is monitored in the intensive care unit to observe for any neurological deterioration due to cerebral edema, intracranial hemorrhage and seizures. Contraindications to awake craniotomy include non-availability of expertise, mentally retarded and deranged patients, younger children, very large tumors and difficult airway.

Inferences

With availability of the newer anesthetic drugs, improved microsurgical techniques and proper selection of the patients, it should not be difficult to perform awake craniotomy procedure which results in less morbidity and mortality as compared to general anaesthesia, in patients having epileptogenic foci and other lesions which are close to eloquent i.e. motor and speech areas of the brain.

The writers are consultant anaesthesiologists at Hinduja Hospital, Mumbai. Email: chels4@vsnl.com
The writer is a Mumbai-based consultant