Craniotomy

Resources

Anaesthesia for Craniotomy and Brain Tumour Resection (WFSA, 2022)
Pain management after elective craniotomy; a systematic review with PROSPECT recommendations (European Journal of Anaesthesiology, 2023)
Definition, evaluation, and management of brain relaxation during craniotomy (BJA, 2016)

Elective craniotomies are commonly performed for treatment of intracerebral lesions, which may be:

Tumours; excision or debulking
Abscesses requiring drainage
Vascular lesions e.g. aneurysms, AVMs, although these are mostly treated by IR

Emergency craniotomy may be required in the management of refractory raised ICP, or for management of intracranial haemorrhages

These mostly mimic those of generic intra-operative neurosurgical care

Tight BP control is essential, especially during aneurysm surgery

High BP may lead to rupture, which carries a high mortality
Low BP may lead to vasospasm
Vasopressors are used to raise MAP
Labetalol e.g. 10mg bolus may be used to reduce BP during emergence or in recovery

Brain relaxation

Brain relaxation is the process of creating an ideal volume of the intracranial contents in relationship to the capacity of the intracranial space, to:

Provide optimal operating conditions during open intracranial surgery
Improve patient outcome

Primary methods of brain relaxation

Head-up positioning

Hyperventilation to P_aCO₂ 3.5 - 4.0kPa

Osmotherapy e.g. 0.25 - 1g/kg 20% mannitol over 20mins given post-induction

Furosemide

Bolus of IV anaesthetic e.g. thiopentone 500mg, propofol

CSF drainage

The presence of ventricular drains is beneficial as they provide the ability to monitor ICP ± drain CSF to control ICP or brain bulk
Care must be taken to avoid excessive CSF drainage, as this can cause brain sagging, cardiovascular instability and increase the TMPG of aneurysm walls

Fluorescing agents

5-aminolevulinic acid is an endogenous amino acid which occurs naturally as part of the porphyrin (and thus haem) synthesis pathway

Colloquially called 'the pink drink', it is concentrated in glioma (gliobastoma) tumour cells
It is drunk 1-4hrs pre-operatively
It fluoresces pink under UV light, allowing greater resection of cancerous tissue - indeed it can increase the chance of whole-tumour resection from 30% to 70%
It can cause photosensitive skin reactions, so once drunk patients should remain in a darkened area until 24hrs post-operatively
it is contraindicated in patients with porphyria

Indocyanine green is a pigmented dye injected intravenously during a number of surgeries to assess vascular flow

In neurosurgery it is typically used during aneurysm clipping to ensure flow through the aneurysm has been occluded
It can cause a transient interruption in saturations monitoring (providing a falsely low SpO₂)
It can cause hypersensitivity reactions and is contraindicated in those with previous reactions to iodinated dyes
It is exclusively hepatically metabolised with a half-life of 3-4mins, although this may be longer in those with hepatic impairment

This is an emergency (or more often 'urgent') procedure performed for evacuation of chronic, symptomatic subdural haemorrhage
It involves drilling two burr holes into the skull and using them to flush clot out
For extremely high-risk patients it can be done under 'just' local anaesthetic, but otherwise either sedation or GA is provided, with no evidence either is superior

Sedation technique

As ever with sedation, patient selection and preparation is key
Patients who are significantly obtunded already, non-cooperative, with significant movement disorder or have other standard contraindications to sedation are unlikely to be appropriate candidates

This can be done with:

Just propofol (e.g. via TCI e.g. 0.5 - 1μg/ml C_eand titrate)
Propofol and additional opioid e.g. remifentanil (e.g. 1mg in 50ml giving a 20μg/ml concentration and a TCI C_e target of 1-2ng/ml as an opening gambit)

Other standard sedation monitoring including facemask oxygen incorporating end-tidal CO₂ monitoring is used

Periods of more intense stimulation include:

Scalp injection of LA (often requiring a head hold to prevent excessive movement)
Drilling (often requiring a head hold to prevent excessive movement)
Diathermy to the dura mater
Stitching the skin; generally better to leave sedation on until the skin is stitched to prevent excessive movement

GA technique

Reserved for those in whom sedation is refused or inappropriate e.g. low GCS
This can be a bit more of an agriculture GA than the standard neuro-anaesthetic set up, namely:

No need for feet drips as arms usually easily accessible
No need for arterial line unless other patient indication
Volatile or propofol TCI acceptable maintenance
≤100μg fentanyl at the end often suitable analgesia; long-acting opioids or remifentanil not typically required

Pain after craniotomy is moderate-severe in over 50% of cases, with infratentorial procedures being more painful
It is somatic pain involving the scalp, pericranial muscles, soft tissue and the dura
Pain is most severe in the first two post-operative days, and is associated with negative sequelae:

Negative sequelae of poorly-controlled craniotomy pain

Increased post-operative morbidity

Hypertension

Agitation (↑ ICP)

Vomiting (↑ ICP)

Prolonged recovery

Prolonged length of stay

Chronic post-surgical pain

Pharmacotherapy

Paracetamol; deceases post-operative pain score
NSAIDs; reduces pain scores, reduce PONV, are opioid-sparing and are not associated with adverse events such as bleeding

Scalp block or incisional site infiltration of local anaesthetic

Magnesium intraoperative bolus (50mg/kg) and continuous infusion (25mg/kg/hr) is associated with reduced pain scores and lower opioid requirements
Dexmedetomidine infusion (0.2 to 0.5 μg kg−1 h−1) intra-operatively is associated with lower post-operative pain scores and opioid consumption, but may contribute to post-operative hypertension
Gabapentinoids are not recommended by PROSPECT guidelines due to debatable analgesic effect and concern over side-effects

Opioids should be used as rescue therapy