A 54 year old woman with a history of hypertension presented to the emergency department with a sudden onset severe headache. Her GCS was E3 V3 M6 on arrival, but deteriorated over the next 2 hours to E3 V2 M5. A CT brain demonstrated an intracerebral haemorrhage and a CT angiogram confirmed a ruptured middle cerebral artery aneurysm. She was intubated and ventilated for transfer to the regional neurosciences unit where she underwent a successful endovascular coiling procedure the following morning. On sedation hold she is now GCS E1 VT M1.
What are the potential causes of her reduced level of consciousness?
Delayed neurological deterioration is common after aSAH. (aneurysmal subarachnoid haemorrhage). This patient has undergone a successful endovascular procedure which should prevent rebleeding (which is a cause of decreased conscious level). The differential diagnosis in this scenario includes:
- Residual sedation.
- Delayed cerebral ischaemia
- Non convulsive status epilepticus
1. Residual sedation
In order to make an accurate neurological assessment, the effects of sedative drugs need to be considered. This patient will have had a general anaesthetic for her procedure, which involves administration of sedative drugs at higher dose than typically used in ICU, and muscle relaxants to prevent movement during the endovascular coiling procedure. An appropriate period of time needs to elapse for these drugs to be metabolised before a sedation hold is carried out.
Approximately 20-30% of patients with aSAH will develop hydrocephalus, and the likelihood of developing hydrocephalus increases with worsening grade of aSAH. Patients will often, but not always, have on-table CT scans as part of their coiling procedure, which may reveal hydrocephalus. This patient did not have hydrocephalus on her CT scan in the ED, and did not have an on table CT during today’s procedure so a repeat CT brain would be required to rule out this diagnosis.
3. Delayed cerebral ischaemia
Delayed cerebral ischaemia (DCI), results from spasm of the cerebral arteries causing reduced cerebral perfusion. This may result in focal neurological deficits or a global reduction in conscious level. It is a common complication in poorer grade aSAH patients. The typical period for development of this complication is day 3 to day 14 post-bleed, but it can occur earlier. Reduced level of consciousness or new focal neurological signs are a clinical indicator of DCI.
Detection of increased velocities of blood flow in the cerebral circulation using transcranial doppler ultrasound may suggest a diagnosis of DCI. CT scans may also show areas of ischaemia. Cerebral angiography can confirm the presence of vasospasm.
Nimodipine, a calcium channel blocker that crosses the blood brain barrier, is given to patients with aSAH to prevent vasospasm, and has been shown to improve outcome. Some centres will perform balloon angioplasty and intraarterial injection of vasodilators as treatment. Ensuring euvolaemia and if necessary, augmenting blood pressure using vasopressors can be used to improve brain perfusion in a patient with DCI.
4. Non convulsive status epilepticus
1-7% of patients with SAH will have seizure activity at the time of the initial bleed. Non convulsive status epilepticus can lead to a reduced level of consciousness. This diagnosis can be confirmed or excluded by performing an EEG. At present there is no proven benefit for prophylactic use of anticonvulsants in this patient group, but in those with confirmed seizures, anticonvulsant medication should be given.
Fever in a vulnerable brain can be associated with significant reductions in level of consciousness. Fever is very common in aSAH patients, occurring in 40-70% of patients and may occur in the absence of infection. Full infection screens should be undertaken and the patient may be cooled using antipyretics and cooling devices if necessary.
Key take home messages from the case
- In poorer grade SAH patients, reduced level of consciousness may have several causes..
- Causes of reduced LoC should be systemically considered.
- Regular sedation holds in intubated and ventilated patients allow early detection of changes in neurological state.
References for relevant evidence or further reading
Diringer MN Bleck T Hemphill JC et al Critical Care Management of Patients Following Aneurysmal Subarachnoid Haemorrhage: Recommendations from the Neurocritical Care Society’s Multidisciplinary Concensus Conference. Neurocritical Care (2011) 15:211-240