Posterior fossa craniectomy
1 Anaesthetic management of major craniectomy/craniotomy
2 Problems particularly associated with posterior fossa procedures
3 Analgesia after a craniotomy.
2E01, 2F01
A 39-year-old man (83 kg, 1.84 m tall) presented with a 3-week history of headache and ataxia. An MRI demonstrated a cystic lesion in the right cerebellar hemisphere. There was a working diagnosis of a cerebellar haemangioblastoma.
Cerebellar haemangioblastomas may be sporadic or present as part of a syndrome such as von Hippel–Lindau disease (vHLD) (in 20%). They are benign and may be solid or cystic, and the intracranial lesion is almost always in the posterior fossa. There is an association with polycythaemia.
vHLD may be associated with retinal angiomas, haemangioblastomas of the spinal cord or brain, renal cell carcinoma, and, in 10% of cases, phaeochromocytoma. Thus, screening for phaeochromocytoma may be undertaken. vHLD is an autosomal dominant inherited condition, with a 90% penetrance and an incidence of 1 in 36 000 live births. In appropriate cases, genetic counselling will be offered. Typical presenting complaints are similar to those in the patient (headache, nausea and vomiting, cerebellar signs).
The patient had an unremarkable previous medical and family history. Screening for phaeochromocytoma was negative.
◆ Preoperative medication included: paracetamol, omeprazole, dexamethasone (recently commenced to reduce swelling around the lesion)
◆ BP 110/74–135/70; pulse 75 regular.
Preoperative investigations included:
◆ Initial investigations: Na+ 141 mmol/L, K+ 4.3 mmol/L, urea 5.5 mmol/L, Cr 61 micromoles/L, eGFR >60 mL/min
◆ Hb 145 g/L, WCC 10.4 × 109/L, Plt 270 × 109/L
◆ Clotting: APTT ratio 1.0, INR 1.0, fibrinogen 2.7 g/L
◆ ECG: sinus rhythm.
◆ Positioning which may include the prone position
◆ Vital structures in the posterior fossa
◆ Generally perceived as more painful than other approaches, as greater dissection through more muscle (trapezius) and more bone
◆ A high incidence of PONV.
Analgesic regimens between neurosurgical units are highly variable. This allows requirements to be tailored to those of the unit, but is not necessarily evidence-based. Patients must be kept comfortable, but without causing an altered consciousness or a respiratory depression (and hence a raised PaCO2 and all that means for ICP). Also the analgesic must not affect clotting, specifically the platelet function, and must not reduce the seizure threshold.
The means we use in our own unit are as follows:
◆ Regular paracetamol, starting with an IV administration perioperatively. That said, we review the requirement for regular paracetamol on a daily basis, changing to ‘as required’ use or discontinuing the paracetamol completely when a regular use is no longer deemed necessary
◆ Should the patient be sufficiently conscious to use a PCA, we give it, usually with morphine. As an intermediate between paracetamol and morphine, we usually prescribe dihydrocodeine, usually on an ‘as required’ basis
◆ We avoid tramadol, because it lowers the seizure threshold
◆ The use of NSAIDs after a craniotomy is highly contentious. Opinions range from the perioperative administration of drugs, such as parecoxib, after a dural closure, through the administration of NSAIDs after a period of between 6 and 24 hours, to an absolute abstention in a patient who has undergone an intracranial procedure. Our unit very rarely administers NSAIDs after a craniotomy, always after discussion with our neurosurgeons, and never within the first 24 hours. On the rare occasion when NSAIDS are used, it is when pain control has been problematic with other means
◆ We have been recently impressed by the use of clonidine IV (variable; slow IV bolus dose; when used, 30 micrograms is commonly the dose) as an adjunct to analgesia in patients who have difficulty in managing pain. Although mildly sedating, we find the patients easy to rouse and no appreciable effect on respiration. As the patients are usually catheterized, we find no problems with urinary retention
◆ A mixture of lidocaine and bupivacaine containing 1/400 000 adrenaline is usually administered by neurosurgical colleagues at the start of the procedure. We do not administer a local anaesthetic at the end of the procedure, as the dura has been opened, and there is a danger that the local anaesthetic may track beneath the dura. The bupivacaine may exert an effect for some hours after the procedure.
Some units use scalp blocks for craniotomies.
Codeine is a prodrug, which is demethylated (to morphine) in the liver to its most active form. Some patients lack the enzyme to do this, and the intrinsic analgesic property of unaltered codeine is poor.
In doses used clinically, morphine was no more likely to cause side effects of respiratory depression and sedation than codeine. Morphine did, however, provide more predictable and persistent analgesia, as reported by Goldsack and colleagues.
Codeine is still used in many units, despite 50% of anaesthetists thinking it is poor analgesic, as described by Stoneham and Walters. Codeine should not be administered IV.
After 1 mg of IV midazolam, an arterial line was sited, followed by induction with propofol, remifentanil, and atracurium. Maintenance of anaesthesia was with a combination of oxygen/air/sevofluanne and an infusion of remifentanil and atracurium. A right internal jugular central line was sited, prior to preparation and prone positioning. Surgery, conducted under Brainlab® (neuronavigation) guidance, was uneventful, as was the post-operative course.
The patient was comfortable with the post-operative analgesia regimen of morphine PCA and regular paracetamol.
The patient went home 5 days post-operatively (GCS 15) and was doing well at the post-operative outpatient follow-up.
Summary
Posterior fossa procedures are especially challenging for a number of reasons, including positioning on the operating table and the close proximity of vital intracranial structures. They also tend to be more painful and to have a relatively high incidence of PONV. Analgesia regimens vary between units, and some of the agents used are highly controversial.
Some conditions associated with posterior fossa lesions (e.g. von Hippel–Lindau syndrome) may require screening for further associated medical conditions such as phaeochromocytoma or cysts.
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