College Answer

With regard to the EEG:

a) List three indications for the use of the EEG in a critically ill patient

•    Detection of non convulsive seizures and characterization  of spells in patients with altered mental status with: (A history of epilepsy, Fluctuating level of consciousness, Acute brain injury, Recent convulsive  status epilepticus,  Stereotyped  activity such as  paroxysmal   movements,   nystagmus,   twitching,   jerking,   hippus,   autonomic variability)
•    Monitoring  of ongoing therapy: Induced coma for elevated intracranial  pressure or refractory status epilepticus, Assessing level of sedation
•    Prognosis: Following cardiac arrest, acute brain injury

b) What are the clinical implications  of non-convulsive  status epilepticus (NCSE) in the critically ill patient?

An underdiagnosed entity.

In several studies, the presence of NCSE and delay to diagnosis and treatment were each associated with significantly more frequent mortality. Periodic epileptiform discharges (PED) have  also  been  associated  with  a  significant  increase  in  death  or  severe  disability  at hospital discharge in particular in neurologic disease/injury. NCSE may also occur in those without  primary  brain  injury  e.g.  sepsis  and  conveys  the  same  prognosis.  Aggressive treatment as for convulsive status epilepticus is recommended.

c) List two EEG patterns that may be seen after hypoxic brain injury thought to be associated with a poor prognosis.

Note: none of these patterns are specific for death or poor outcome and must be regarded along with clinical assessment.
•    Generalised suppression/isoeletric
•    Generalised burst suppression especially if accompanied by epileptiform activity
•    Epileptiform and generalised periodic discharges, especially myoclonus
•    Alpha pattern coma

Discussion

a) This answer comes from Box 49.2 in Oh's Manual (page 556).

• Confirmation of non-convulsive status epilepticus
• Continuous monitoring of general anaesthetic infusion for status epilepticus
• Confirmation of brain death or prognosis of hypoxic/ischaemic brain injury

b)

• Brain injury (excitotoxicity) could occur due to unrecognised seizures
• Cerebral metabolic rate may be higher, and cerebral metabolic demand may not be met if the NCSE is not recognised and treated, giving rise to ischaemia
• NCSE patients have a poorer prognosis than patients with a disorder of consciousness from other causes
• The underlying cause of NSCE is the most important prognostic factor

c) Again, the same box in Ohs Manual has the answers. Severe hypoxic encephalopathy is associated with the following EEG features:

• Presence of theta activity
• Diffuse slowing
• Burst suppression
• Alpha coma