Anaesthesia for awake craniotomy

Awake craniotomy is performed for the surgical treatment of intractable seizures and tumors on the eloquent areas of the brain. Mapping of the normal areas of the brain is done to delineate them from the tumor intraoperatively. This involves stimulating the brain with small voltage ad high frequency currents and assessing patients verbal, motor and sensory response. Thus, an awake and alert patient is the fundamental requirement of this procedure. One can easily understand that keeping the patient awake and responding, pain free and comfortable during the surgery is quite a difficult task and  you can say that, awake craniotomy is more of an anaesthetic challenge than surgical. Recently, we performed an awake craniotomy for the first time in our institution for a tumor which was close to the motor areas of right cerebral hemisphere.
Medical literature is replete with numerous original articles and case reports on anaesthesia for awake craniotomy and thank god for that. It was invaluable for us to plan our anaesthetic. When you go through this knowledge bank on awake craniotomy, you will realise that there are mainly two  techniques commonly used for anaesthetizing these patients – conscious sedation with scalp blockade and “asleep-awake-asleep” (general anaesthesia (LMA with or without IPPV) and scalp blockade-awakening- general anaesthesia (LMA with or without IPPV). The latter technique supposedly ensures better patient comfort and outcome. Craniotomy involves performing scalp blockade (multiple injections), stabilizing the patient’s head on sharp-pinned frames (Mayfield, Sugita’s etc), raising the scalp flap, drilling and removing a piece of skull bone and lying down in quite uncomfortable position for a long time. No wonder it can be  quite a traumatic experience for an awake patient to go through all this for the entire duration of the surgery. So, ours was also a version of “asleep-awake-asleep” technique.
Our patient was a 35 year old male(weighing 61 Kgs) with a glioma over the right parietal sub cortical area measuring about 15 x 15 mm. He had presented with seizures and slurring of speech three months before the day of surgery. He did not have any focal neurological deficits and the speech had also normalized. He had developed allergic bronchial asthma two months before the date of operation, which was attributed to exposure to cold and dusty climate. He was being treated with bronchodilators and inhalational steroids for the same and had become asymptomatic at the time surgery. He was a very cooperative and highly motivated gentleman and had fully understood the need for the procedure and various steps involved. A thorough and patient explanation and showing a video of the procedure helped a great deal in preparing the patient for the procedure. During preanaesthetic examination his upper incisors were found to be significantly mobile and were extracted.
I will give our anaesthesia plan now. I hope it will be of use to somebody. I eagerly welcome all kinds of comments.

Premedication

All his medications (anticonvulsants, bronchodilators) were continued till the morning of the surgery.
T. Clonidine 150 mcg, T. Diazepam 10 mg, T. Pantoprazole 40 mg, inj. Dexamethasone 8 mg, T. Ondansetron 4mg – one hour before the surgery
Salbutamol and Ipratropium bromide nebulisations just before shifting him to operation theatre

Monitoring

Pulse oximetry, ECG, Noninvasive Blood Pressure, ETCO2, Bispectral Index monitor, Invasive Blood Pressure and urine output ( both after induction).

Induction

Intravenous line (16 G) was secured in left hand dorsum under local anaesthesia. Preoxygenated with 100% oxygen and induced with inj. Fentanyl 100 mcg, inj. Propofol 100mg. Size 4 Intubating Laryngeal Mask Airway (ILMA) was inserted and patient was allowed to breathe spontaneously. Anaesthesia was maintained with propofol infusion (50 mcg/kg/min) and sevoflurane (End tidal concentration of 1-1.5%) to BIS of about 50.
Right radial artery was cannulated with 20 G catheter to monitor invasive blood pressure.

Scalp Blockade

Total amount of solution used – 80ml
0.5% Bupivacaine – 40ml
2% Lidocaine – 20ml
Adrenaline – 400 mcg(in 4ml saline)
Saline – 16ml

Nerves blocked – supraorbital, supratrochlear, zygomatico temporal, auricuculotemporal, posterior auricular, lesser occipital and greater occipital on both sides with 2-3ml of drug mixture for each nerve.

Landmarks for the nerves-

a. Supraorbial and supratrochear - above eyebrow at the midpoint, needle  inserted perpendicular to the skin. Also at the medial margin of the orbit

b. Auriculotemporal - 1.5cm anterior to the tragus; needle inserted perpendicular to skin.

c. Zygomatico temporal - midway between supraorbital ridge and post margin of Zygoma; deep infiltration with in the temporalis muscle and fascia

d. Post auricular branches( of greater auricular nerve) - 1.5 cm posterior to th ear at the level of tragus between skin and bone

e. Greater and lesser occipital nerves - along the superior nuchal line approximately halfway between occipital protruberance and mastoid process; infiltration done with 22 G spinal needle.( all other blocks done with 23G 4cm needle)

Remaining soultion used to infiltrate over the pin sites(3) and along the line of incision.

Block was done 15 mins before the procedure and we hoped that it would last for atleast 4-5 hours.

Success of the block was noted by observing that there was no hemodynamic response to pin insertion and to the skin incision. Also, patient was completely pain free through out the procedure which lasted for 6 hours. Only 175 mcg of Fentanyl was used through out the procedure.

Draping for the procedure

Draping for this procedure was little different from that for usual craniotomies. A transparent screen separated head end and the operating site from the rest of the body so that we had unhindered access to the same.

Maintenance and awakening

 Anaesthesia was maintained with propofol infusion (50mcg/kg/min) and sevoflurane (end tidal concentration of 1.5-2%). BIS was maintained around 50. Patient received 0.5 gm/kg mannitol before craniotomy along with Furosemide (20 mg). Surgeon infiltrated dura with 6 cc of 1% lidocaine before incising it. Twenty minutes before planned awakening, sevoflurane was discontinued and propofol infusion was decreased to 25 mcg/kg/min. Patient started moving his limbs when the BIS was about 75. Propofol infusion was fully stopped. LMA was removed after suctioning, when the BIS was between 75 – 80 and patient responsive to oral commands. Another 5 mins was allowed for the patient to fully regain consciousness. Patient became fully awake and responsive when the BIS was around 90.

Cortical mapping and tumor excision was done, to which patient cooperated fully. Excision was completed in about 45 minutes. Patient kept complaining about desire to pass urine, in spite of being told that his bladder had been catheterized. Probably, the patient would have been much more comfortable if only we could somehow abolish the sensation of catheter in the urethra.

He also had mild generalized head ache towards the end of excision, which he felt was quite tolerable. There were no complaints from the surgeon about bulging of the brain. Hemodynamics was maintained at patient’s normal levels through out the procedure and they remained stable through out.

 “Asleep” again

 Patient was anaesthetized again with propofol 2mg/kg and fentanyl 75mcg and ILMA was reinserted. There was not much difficulty in accomplishing this. Patient was allowed to breathe spontaneously and anaesthesia was maintained with sevoflurane (2%) and propofol infusion at 50 mcg/kg/min. Surgeon started closing the dura. Patient received Morphine 6 mg for post operative pain relief. Five minutes after this, the breathing became strenuous with reduced rate along with Inspiratory sound similar to stridor. Anaesthesia was deepened further by increasing both propofol infusion and sevoflurane concentration. There was no improvement, rather breathing seemed to worsen, ETCO2 started increasing (to >45 mm Hg) and surgeon complained of bulging of brain out of the craniotomy site. We suspected displacement of LMA and reinserted the same. Meanwhile we reduced the depth of anaesthesia, which increased the respiratory rate with improvement in patient’s breathing. Rest of the surgery was completed uneventfully.

 Post operative period

 Post surgery, we removed the ILMA when patient was fully awake. The post operative period was uneventful. Patient was awake, alert and comfortable through out. There were no neurological deficits. He was kept in neurosurgery intensive care unit overnight and was shifted to the ward the next day. He was discharged from the hospital after two days of surgery.

P S :

This was our first experience with awake craniotomy. It was indeed a very interesting and learning experience. Please leave comments before you surf away from this page..