Awake craniotomy
Learning outcomes
1 Indications for awake craniotomy
2 Techniques for awake craniotomy.
CPD matrix matches
2A03, 2A07
Case history
A 55-year-old, right-handed male architect had presented with a 5-week history of dizziness, disorientation, visuospatial changes (‘walking into objects, unaware that they were there’), and right arm weakness. He was otherwise well and had no other medical history, except for an uneventful appendicectomy in his teens. He was a lifelong non-smoker who seldom drank alcohol.
An MRI scan of his head showed a left-sided enhancing parieto-occipital mass, approximately 40 x 70 mm in dimension. He took no medication prior to diagnosis and had been commenced on a course of dexamethasone (with omeprazole) 2 weeks prior to admission, which led to some resolution of his symptoms.
Due to the position of the tumour, it was intended to perform this procedure as an ‘awake’ technique, with which the patient was in full agreement.
What are the major indications for an awake craniotomy?
1 A tumour in an eloquent part of the brain, described previously (i.e. in order to damage as little of the normal brain tissue as possible)
2 Movement disorders (including benign intention tremor, Parkinson’s disease, and secondary to multiple sclerosis)
3 Epilepsy with a particularly circumscribed focus of electrical activity.
Less established indications are obesity and obsessive–compulsive disorder.
Case update
◆ On examination:
• BP 122/73, pulse 82, weight 99 kg, height 1.92 m
• GCS 15. No obvious focal deficits after 2 weeks on steroids
◆ Blood results:
• Na+ 135 mmol/L, K+ 4.7 mmol/L, urea 5.8 mmol/L, Cr 63 micromoles/L, eGFR >60 mL/min
• Hb 159 g/L, WCC 18.3 × 109/L (on dexamethasone), Plt 232 × 109/L
• Clotting screen: normal
◆ ECG: sinus rhythm.
What are the goals of the anaesthetic technique used for an awake craniotomy? Which anaesthetic techniques may be used for an awake craniotomy?
There are a number of tenets for an awake craniotomy. First and foremost, it must be a technique acceptable to the patient. The patient must be comfortable and crucially not move during the critical parts of the procedure. They must waken up quickly.
The broad categories may be classified as follows:
◆ Local anaesthetic for the entire procedure: some advocate scalp blocks. However, scalp blocks to both sides of the head, incorporating all the nerves which have to be blocked, may approach the maximum recommended dose for that local anaesthetic.
The patient must be exceptionally compliant. Obviously, this lengthens the time for which the patient is awake, and many patients will find this intolerable. Hence, the so-called:
◆ Asleep/awake/(asleep) technique: in this technique, the patient has a general anaesthetic for the initial part of the procedure, during which potentially uncomfortable parts of the procedure are performed (siting the stereotactic frame, skin incision, and the initial part of the craniotomy). The patient is then woken up, and the rest of the operation is performed (the awake phase).
The patient may then be put back off to sleep. However, this is often not necessary and may require instrumentation of the patient’s airway from the front, with the head held rigidly in Mayfield pins. As such, many anaesthetists do not re-sedate the patient after they have been woken up.
Whichever technique is used, the patients must be carefully selected and informed of the likely format of the case. Performing the entire procedure under local anaesthetic may be unacceptable to a significant number of patients (and surgeons)!
The technique used most recently in our centre is an asleep/awake technique. For the preparatory parts of the procedure perceived as being the most uncomfortable, the patient is asleep. That said, the administration of a longer-acting local anaesthetic is used (bupivacaine), particularly to the Mayfield pins.
Several recent developments have revolutionized this procedure. These include:
◆ The LMA, which may be the reinforced model. The LMA (as opposed to formal intubation) has greatly facilitated a smooth awakening. The administration of the non-sedative antisialogogue glycopyrrolate about 1.5 hours prior to the anticipated removal of the LMA may reduce coughing caused by secretions
◆ Propofol infusion, guided by a depth of anaesthesia monitor (such as BIS), allows an appropriate depth of anaesthesia with minimal agent. That said, many colleagues prefer to use a volatile-based technique with an agent such as sevoflurane
◆ Remifentanil IV infusion allows the suppression of spontaneous ventilation (and hence the ability to ventilate through the LMA. This stops an inappropriately high PaCO2). It also allows rapid offset and has minimal sedative properties
◆ The depth of anaesthesia monitoring (such as BIS) allows the minimal required amount of sedative to be given which facilitates a rapid awakening.
Dexmedetomidine by infusion has been used as a sedative with analgesic properties in several countries. It has the advantage of a rapid recovery. However, it was not widely available in the UK at the time the case discussed here took place and was initially being introduced with the licensed indication intended for ICU administration. Subsequently, other centres have used it in theatre to good effect.
The less selective α2-agonist clonidine has been used by some anaesthetists, based on experience gained on ICU (to ease the withdrawal from alcohol dependency). However, the use of clonidine infusions in theatre and in ICU is currently unlicensed in the UK.
Case update
Technique
A 20G left radial arterial line was placed after induction with propofol TCI, with a remifentanil infusion at 0.1 micrograms/kg/min to suppress attempts to breath, and supplemented with an 80 microgram bolus to facilitate LMA placement. An armoured size 4 disposable laryngeal mask was used to maintain the airway. Once asleep, glycopyrrolate 0.3 mg was administered as an antisialogogue in anticipation of the removal of the LMA. The patient was kept asleep with a TIVA technique, based on the propofol/remifentanil regimen and ventilated through the LMA with oxygen and air. Clonidine (30 micrograms/hour) was commenced after induction and ran until about 20 min prior to the anticipated awakening.
The depth of anaesthesia was monitored, using bihemisphere BIS. A transcutaneous carbon dioxide monitor was sited on the right earlobe as a means of continuously monitoring the arterial carbon dioxide, prior to removal of the LMA. This was checked against intermittent ABGs and found to give close concurrence. As ETCO2 monitoring is lost when the LMA is removed and ABG is intermittent, the transcutaneous carbon dioxide monitor maintained continuous information on the carbon dioxide levels. A urinary catheter was placed asleep.
Mayfield pins were placed and the head positioned. The scalp was infiltrated with 0.375% bupivacaine with 1/200 000 adrenaline. This was done by blocking the left-sided auriculotemporal, zygomaticotemporal, supraorbital, supratrochlear, and greater and lesser occipital nerves with a few mL infiltrated around the three Mayfield pins. A total of 40 mL of this solution was used.
When the surgeons had gained adequate access, the request to lighten the anaesthesia was made; the propofol was switched off, along with the remifentanil infusion. The anaesthetic chart is shown in Figure 7.8.
Fig. 7.8 An anaesthetic chart for the awake craniotomy case described in the text.
The rest of the resection was performed with attention paid to any changes in motor function or speech. BP increased from 115/60, immediately prior to awakening, to 150/80. In order to prevent an overshot, a test bolus of esmolol was administered (to no detriment). Remifentanil was recommenced at 0.02 micrograms/kg/min, and propofol TCI at 0.7 micrograms/mL, leaving the patient calm and easily rousable. Mannitol 20% 100mL was administered twice to reduce brain swelling. Morphine 2 mg was administered towards the end of the case. The patient remained comfortable throughout and did not require to be put back off to sleep.
Post-operative course
The patient was GCS 15 immediately post-operatively. Post-operative analgesia was achieved with regular paracetamol and morphine PCA. Pathology samples had shown a high-grade glioma, and he was referred for chemo- and radiotherapy with adjuvant temozolomide. He was discharged 72 hours after the procedure, with follow-up in clinic. He remained well 6 months post-surgery.
Summary
There are a number of indications for awake craniotomy, including a tumour in eloquent areas of the brain, epilepsy surgery, and movement disorders. Patients should be carefully selected, and a patient who does not wish to have an awake craniotomy is an absolute contraindication to this technique.
There is no undisputed technique, and each variation has its advocates. A common variation is to have the patient asleep for the potentially uncomfortable initial phase of the operation, then awake, and, if necessary, re-sedated (‘asleep/awake/asleep’). The asleep phase is achieved with propofol infusion or a volatile technique. Dexmedetomidine has been available in some countries as part of the technique for awake craniotomies.
The laryngeal mask and depth of anaesthesia monitoring have greatly facilitated this procedure.
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