The College had asked about this in Question 19from the first paper of 2011.Specifically, they wanted indications for EEG and the particular waveforms you might expect in hypoxic brain injury. The answer was derived specifically from one source: Box 49.2 in Oh's Manual (page 556), in the chapter by Balasubramanian Venkatesh ("Disorders of consciousness").
Earlier in this century, the college wanted their candidates to "critically evaluate the role" of EEG in Question 2 from the first paper of 2005.
|Non-convulsive status epilepticus||Epileptiform discharges|
Confirms the diagnosis; respects the definition (as epileptiform activity on EEG in the absence of motor manifestations)
|Continuous EEG monitoring||Epileptiform discharges|
Monitoring of therapy for refractory status epilepticus (essentially confirms that the level of anaesthesia is sufficiently deep to suppress epileptiform activity, when motor manifestations are subtle or absent).
If there are seizures, and you are trying to detect them, how long do you need to monitor the comatose patient?
|Hepatic encephalopathy||Triphasic waves|
Early - alpha-wave slowing
Late - high-amplitude irregular delta waves.
Unfortunately, triphasic waves are also seen with uremic encephalopathy and with medication toxicities (e.g., lithium, valproate and baclofen).
Some EEG-specific guidelines have been synthesised (ISHEN) which acknowledge the limitation of visual "reading" of EEG data, and instead recommend computerised semiquantitiative interpretation of the relative power of frequency bands and the mean dominant frequency (which does have some prognostic value).
The AAN recommendations for prognostication in hypoxic brain injury did not recommend the routine use of EEG, because it is "strongly but not invariably associated with poor outcome". The new 2014 consensus statement is more optimistic about it, specifcally about the absence of EEG reactivity and status epilepticus within the first 24-48 hours.
Burst suppression and alpha coma are frequently seen in severe hypoxic brain injury, and can be associated with a poor outcome. However, the false positive rate is high. The new recommendations are "do not use".
Oh's Manual mentions this, but it seems to be based on studies form the 1970s. These features are not diagnostic of HSV encephalitis (i.e. one would not abandon the LP in favour of EEG) but they certainly seem to be consistently associated.
Advantages and limitations of the EEG in the ICU