Hyponatremia develops after SAH in many patients due to excessive renal secretion of sodium rather than a dilutional effect from inappropriate antidiuretic hormone secretion. Fluid loss and a fall in plasma volume follow.
These patients are particularly at risk of developing cerebral ischaemic deficits, probably as a result of increased blood viscosity. Reduced cerebral perfusion pressure
Following SAH, intracranial haematoma or hydrocephalus may cause a rise in intracranial pressure (ICP). Since cerebral perfusion pressure = mean BP - ICP, a subsequent reduction in cerebral perfusion may occur.
Clinical effects of cerebral ischaemia/infarction
This may affect one particular arterial territory producing characteristic signs:
Third _W ventricle
^ Anterior cerebral territory
- leg weakness, incontinence
- confusion, akinetic mutism — Middle cerebral territory
- hemiparesis, hemiplegia
- dysphasia (if dominant hemisphere)
Internal carotid territory widespread effects with hemisphere swelling
Commonly the ischaemia occurs in multiple areas, often in both hemispheres. This correlates with the pattern of arterial 'spasm'.
Transcranial Doppler: a significant increase in flow velocity within an intracranial vessel may indicate developing 'vasospasm', even before clinical problems develop, and allow the early introduction of prophylactic measures (see page 255).
Following SAH, cerebrospinal fluid drainage may be impaired by:
- blood clot within the basal cisterns 1 'communicating' hydrocephalus
- obstruction of the arachnoid villi J (see page 360)
- blood clot within the ventricular system - 'obstructive' hydrocephalus.
Acute hydrocephalus occurs in about 20% of patients, usually in the first few days after the ictus; occasionally this is a late complication. In only one-third are symptoms of headache, impaired conscious level, dementia, incontinence, or gait ataxia severe enough to warrant treatment.
In a further 10% of patients, hydrocephalus develops late - months or even years after the haemorrhage.
Was this article helpful?
This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.