Neurocritical Care
Neurocritical care questions turn on a small number of numbers: GCS components, intracranial pressure, cerebral perfusion pressure and the time windows for reperfusion. The Board also tests herniation recognition and status epilepticus sequencing.
Examination and the pressure box
The skull is a fixed box containing brain, blood and CSF. Cerebral perfusion pressure = MAP - ICP; usual targets are ICP below 20-22 mmHg and CPP 60-70 mmHg. Head up 30 degrees, head midline, avoid neck-line compression, and keep normothermia, normoglycaemia, normocapnia and adequate sedation. Hyperventilation to PaCO2 30-35 mmHg buys minutes during herniation, not hours.
Herniation and medical therapy
An ipsilateral blown pupil with deteriorating consciousness is uncal herniation: elevate, give osmotherapy and call neurosurgery. Hypertonic saline 3% (100-250 mL bolus) or mannitol 0.5-1 g/kg; mannitol is an osmotic diuretic, so watch volume status and osmolality. Dexamethasone helps tumour oedema, not traumatic brain injury or ischaemic stroke. Seizure prophylaxis after traumatic brain injury is short-term.
Specific emergencies
Aneurysmal subarachnoid haemorrhage: nimodipine 60 mg every 4 hours for 21 days, watch for rebleeding, hydrocephalus and vasospasm. Ischaemic stroke: thrombolysis within 4.5 hours, thrombectomy up to 24 hours with favourable imaging, blood pressure below 185/110 before lysis and below 180/105 after. Intracerebral haemorrhage: target systolic about 140 mmHg and reverse anticoagulation urgently. Status epilepticus: benzodiazepine, then levetiracetam, valproate or fosphenytoin, then an anaesthetic infusion with burst suppression. Spinal cord injury: MAP 85-90 mmHg; steroids are not routine.
Worked example
A head-injured patient has ICP 25 mmHg and MAP 70 mmHg. CPP is 45 - too low. First exclude a slipped head position, a kinked line or a blocked drain. Then raise MAP with noradrenaline to 85 to give CPP 60. If ICP stays above 22 despite sedation and osmotherapy, escalate to a ventricular drain and discuss decompressive craniectomy.
Traps
Using steroids for traumatic brain injury. Lowering blood pressure aggressively in ischaemic stroke when thrombolysis is not planned. Missing hypoglycaemia and hypercapnia as causes of a low GCS. Diagnosing brain death without an apnoea test or without excluding sedation, hypothermia and metabolic confounders.