List the potential causes of delayed awakening in a patient after a prolonged stay in Intensive Care and outline how you would determine what factors were contributory.
Potential causes include:
prolonged effects of sedative drugs, metabolic encephalopathy (especially renal or hepatic failure), endocrine problems (especially hypothyroidism), systemic sepsis, and a myriad of specific neurological problems ( eg. status epilepticus, raised intracranial pressure, intracranial haemorrhages, severe Guillain Barre, critical illness polyneuropathy). Residual muscular paralysis must be excluded.
Sedative drugs may have a prolonged effect because of altered kinetics (including context sensitive half-time, or decreased biotransformation or excretion eg. renal or hepatic failure) or altered dynamics (potentiation of effect by other drugs or organ
failure, sensitivity to effect of usual dosage).
Assessment of contributory factors may be a complex process. Important steps include:
1) Detailed history of neurological state, drugs administered, previous neurological problems
2) Careful examination (in particular neurological, but also for signs of other chronic diseases). Detailed neurological exam should include global CNS assessment (including ability to move eyes or poke out tongue if no other apparent motor responses: locked in syndrome, severe myoneuropathy), and search for focal signs (pupils, tone, movement, reflexes). Nerve stimulator should be used to assess residual paralysis.
3) Biochemical investigations for severity of electrolyte imbalance, creatine kinase, renal and hepatic dysfunction (mcluding ammonia), and to exclude treatable endocrine disorders (including T4/TSH).
4) Consider use of specific reversal agents (eg. naloxone and flumazenil [may need multiple ampoules]). ·
5) May require other specific investigations (but put into context, and not done as a routine). Such investigations include CT scan of head, MRI, EEG, EMG and lumbar puncture.
This is a question about the approach to the unconscious patient in the ICU, with a view to generate a nice juicy series of differentials. The key feature of the question is that the patient is failing to wake after a prolonged ICU stay.
Let us go though the differentials systematically.
With focal neurological signs
Without focal neurological signs
Endocrine and metabolic causes:
How does one approach such a patient?
- A history is mandatory
- A physical examination is in order, looking for focal signs and characteristic findings
- Some basic bloods, looking for hepatic and renal derangement
- One ought to at least think about reversal agents such as naloxone.
- A CT brain, to exclude structural cerebral disease
- An LP or MRI may be in order depending on the history
- An EEG may be the last investigation, to exclude non-convulsive status epilepticus
Oh's Intensive Care manual: Chapter 49 (pp. 549) Disorders of consciousness by Balasubramanian Venkatesh