Question 24

College answer

Syllabus topic/section:

2.1.8    Neurological intensive care: Subarachnoid haemorrhage: L1

Discussion: 

Candidates who attended to all components of this question performed well. Addressing immediate assessment requires history, examination and investigations to be addressed. As assessment intends to define the diagnosis, better answers were informed by the list of likely diagnoses in part A. A comprehensive answer to a management question addresses resuscitation, definitive as well as supportive therapy and monitoring. Better answers addressed each of these.

Discussion

a)

The potential causes of polyuria post SAH include:

• Normal response to fluid loading (perhaps somebody still does HHH therapy?)
• Hypertensive diuresis (quite likely, as the now-awake patient probably has strict blood pressure targets defined by an arterial transducer zeroed at the Circle of Willis)
• Central diabetes insipidus
• Cerebral salt wasting
• Mannitol diuresis (though it is quite late for that, considering it is usually immediate following administration)

b)

History:

• Procedural records of fluid and osmotherapy administration
• Blood pressure control recently in ICU
• Drug history (eg. lithium?)

Examination:

• Volume status
• New neuro findings (eg. bitemporal hemianopia)

Investigations:

• Urinary sodium and osmolality (CSW vs DI)
• CTB (extent of SAH), MRI (pituitary infarction or oedema)

c) Management

Options include:

• Conservative management
  • Observe urine output for several hours
  • Observe volume status and serum sodium
  • React to changes in levels if they cross thresholds (eg. sodium over 150 mmol/L)
• Control for possible causes
  • Address hypertension, fluid excess, etc
  • Renegotiate BP targets with neurosurgeons
• Restore volume
  • If hypovolemia develops, replace lost volume
  • Avoid replacing it prospectively (as this begets firther diuresis)
• If a diagnosis of DI is made on biochemistry and history, 
  • DDAVP 0.5 mcg regularly
  • Continue measuring sodium regularly (eg. q4h)
  • Watch for hyponatremia (also a common consequence of SAH)