Subarachnoid haemorrhage (SAH) is included here as an example of brain injury because misdiagnosis is common. It occurs in 6-12 per 100 000 per year and has a peak incidence around the age of 50 years. Headache is common, but studies have found that, if patients with the worst headache of their lives and a normal neurological examination only were considered, 12% had SAH. Neurological examination is often normal and in these cases, a third of patients are misdiagnosed in studies. These studies also show that misdiagnosis leads to worse outcome - 65% misdiagnosed patients rebled and rebleeding carries a 40-50% mortality.
SAH commonly presents with a thunderclap headache - a distinct, sudden, severe headache. It need not be in any location; neck pain or vomiting may predominate. The first episode of severe headache cannot be classified as migraine or tension headache (International Headache Society). The sudden release of catecholamines can cause cardiac arrhythmias. Non-contrast CT scans are sensitive, but the pick-up rate decreases each day (92% on the same day, 76% 2 days later, and 58% 5 days later). MRI may be more sensitive in detecting SAH more than 4 days later. A negative CT scan does not exclude SAH. Lumbar puncture (LP) should then be performed (spectrophotometry to look for xanthochromia is most accurate. This is present within 4 hours, maximum at 1 week and persists for 3 weeks). The sample should be protected from light in transit and spun down immediately. SAH is suggested by > 1000 red cells mm-3 but traumatic taps are common (20%). The method of counting red cells in tube 1 and 3 to distinguish a pathological from a traumatic tap can be unreliable. Since up to 6% people have incidental aneurysms, this is highly relevant. CSF pressure measurements should always be performed in diagnostic LPs.
Ultra-early rebleeding in SAH is not uncommon and this should justify immediate CT scanning followed by LP and transfer to the nearest neurosurgical centre. In one study, 17% patients had ultra-early rebleeding (admitted within 24 hours of bleed but rebled before surgery, which was scheduled for the next day). Ultra-early rebleeding was more likely to occur if it had happened once already, if systolic blood pressure was > 200 mmHg, and if the GCS was lower.
Most patients with SAH will be transferred to a neurosurgical centre for further treatment. Some of these patients will require intubation with anaesthesia and invasive monitoring prior to departure. Any fall in MAP during anaesthesia could reduce CPP to a critical level with a significant risk of adversely affecting outcome. Prognosis in SAH for those that reach hospital is that one-third will be in a coma, one-third will develop neurological deterioration, and one-third will make a good recovery.
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