A 62-year-old woman is still not awake 6 hours after clipping of a cerebral aneurysm for a Grade 1 Sub-Arachnoid Haemorrhage.   List the potential causes and outline your management strategy.

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College Answer

Potential causes of delayed awakening early after surgical clipping of a SAH include specific neurological causes (rebleeding, cerebral infarction/ischaemia [including intra- operative technical problems, hypotension]; too early for vasospasm), metabolic causes (including hypothermia, hypo- or hyper-natraemia and hypo- or hyper-glycaemia, hyper- or hyper-capnia) and pharmacological causes (including prolonged effects of sedatives [relative or absolute] and muscle relaxants [not reversed or prolonged/excessive effects: including suxamethonium apnoea].

Management strategy requires exclusion of treatable causes prioritised according to their urgency. Early consultation with the treating neuro-surgical team is critical. Clinical history and examination reveal details of drugs used (including amounts and timing of doses), temperature, ventilation, haemodynamics, and identifies specific surgical issues/problems. Specific investigations that should be considered range from bedside (eg. nerve stimulator to assess residual neuromuscular blockade, or BIS monitor to assess EEG) and simple blood tests (eg. blood gases [oxygenation and exclude significant abnormalities in ventilation], electrolytes [especially Na] and glucose), to more complex and invasive (eg. repeat head CT [to exclude re-bleed, ischaemia] or angiography). These latter investigations would be organised in concert with the treating neuro-surgical team.

Discussion

The approach to this unconscious patient is going to be vary similar to the generic Approach to the unconscious patient in the ICU except you will have some strong suspicions.

Let us recall the broad list of differentials for unconsciousness, and select from it only those which can be sensibly applied in this instance:

Differential Diagnosis of Unconsciousness

With focal neurological signs

Vascular causes:

  • Stroke
  • Vascular insufficiency of the brain, eg. critical vessel stenosis of some specific vessel
  • Intracranial haemorrhage

Infectious causes:

  • Brain abscess
  • Meningoencephalitis with focal crainal nerve damage

Neoplastic causes

  • Space-occuoing tumour

Idiopathic causes

  • Pre-existing focal neurology, superimposed on an acute unconscious state

Autoimmune causes

  • Cerebral vasculitis

Traumatic causes

  • Focal neurological injury due to head trauma
    • That includes surgical injury due to retraction of structures, as in elective neurosurgery
  • Increased intracranial pressure, giving rise to false localising signs

Without focal neurological signs

Vascular causes:

  • brainstem stroke, resulting in damage to the reticular activating system
  • Vascular insufficiency of the brain, eg. diffuse cerebral small vessel disease

Infectious causes:

  • Intracranial infection, eg. menignitis or encephalitis
  • Neurological sequelae of systemic infection, eg. septic encephalopathy

Drug-related causes:

  • Persisting effects of sedatives in context of diminished clearance

Idiopathic causes

  • Delirium of prolonged intensive care stay - a "hypoactive" form thereof
  • Non-convulsive status epilepticus
  • Raised intracranial pressure

Autoimmune causes

  • Cerebral vasculitis

Traumatic causes

  • Sequelae of diffuse brain injury, eg. diffuse axonal injury
  • Hypothermia or hyperthermia

Endocrine and metabolic causes:

  • Hypoadrenalism
  • Hypothyroidism
  • Hepatic encephalopathy
  • Uremic encephalopathy
  • Wernicke's encephalopathy

The remaining causes:

  • Use of long-acting sedatives (eg. thiopentone) in theatre
  • Delayed drug metabolism post-operatively
  • Hypothermia and delayed rewarming postoperatively
  • Metabolic abnormalities (glucose, CO2)
  • Cerebral infarction
  • Contusions due to retraction
  • Re-bleeding from the aneurysm
  • Non-convulsive status epilepticus

Approach to management

  • Ensure the ABCs are stable:
    • normoxia
    • normocapnea
    • normotension
  • Collect routine bloods and correct the correctable metabolic abnormalities
  • Inform the neurosurgeon
  • Ask the anaesthetist regarding the specifics of the operation
  • Get a CT brain
  • Consider an EEG
  • Avoid sedatives and muscle relaxants