Abstracts

Rationale: Anesthetic medications such as pentobarbital and propofol are widely used for the treatment of refractory status epilepticus. Continuous EEG is generally used to verify that seizure activity has been suppressed and does not recur during anesthetic withdrawal. We report a series of patients in whom anesthetic withdrawal was associated with a pattern of generalized periodic discharges, different from prior seizure activity. At times, this pattern was misinterpreted as recurrent seizure activity, leading to reinstitution of drug-induced coma, but it resolved spontaneously. We report our experience with these EEG patterns and their course. Methods: We identified five patients who developed a de novo generalized periodic pattern during pentobarbital or propofol withdrawal. Two patients received pentobarbital for increased intracranial pressure and had no prior history of seizure activity. One patient received pentobarbital and propofol for encephalopathy accompanied by a rhythmic EEG pattern that was erroneously thought to be ictal. Two patients received pentobarbital for refractory partial status epilepticus. In one of these, partial status epilepticus was not defined on EEG and was diagnosed with SPECT. In another, ictal discharges were right occipital and left frontal. The anesthetic agents were withdrawn 36-72 hours after reaching a burst-suppression pattern. We reviewed the EEGs and analyzed the course of the periodic EEG patterns and their outcome. Results: All patients developed a de novo pattern of periodic 1-2 Hz generalized sharp triphasic activity, not previously seen on EEG prior to drug-induced coma. In all cases, the pattern eventually resolved spontaneously without further treatment, over 8-48 hours. However, in three cases the pattern was initially thought to represent ictal activity, and drug-induced coma was reinitiated. The pattern recurred during repeated anesthetic withdrawal, at which point it was recognized as a non-ictal pattern. In all cases but one, the patients exhibited improvement to near baseline mentation in association with clearance of anesthesia and resolution of the EEG pattern. Conclusions: A de novo generalized periodic EEG pattern may develop after pentobarbital or propofol withdrawal. This pattern is expected to resolve spontaneously without treatment, and without recurrence of clinical seizure activity. This pattern is unlikely to represent status epilepticus and should not prompt resumption of drug-induced coma, unless there is reappearance of original electrographic seizure activity.