All patients <18 years admitted to the ICU at Columbia University Medical Center, New York, between June 1, 2000 and April 30, 2004, and considered critically ill, regardless of etiology, underwent continuous EEG (cEEG) for detection of nonconvulsive seizures (NCSz) in the evaluation of unexplained diminished consciousness. Of 117 children monitored with cEEG, 44% had seizures and 39% had NCSz. Of patients with seizures, 73% had only NCSz, and 23% had status epilepticus (NCSE in 89%). The timing of NCSz was immediate after initiation of cEEG in 15%, within 1 hour in 50%, and within 24 hours in 80%. Patients with clinical seizures prior to cEEG had NCSz more frequently than those without (83% vs 17%). NCSz were most common in patients with periodic lateralized epileptiform discharges (PLEDS) [73%], absence of background reactivity on cEEG [65%], any periodic discharges [65%], and absence of sleep architecture [50%]. 
COMMENT. Nonconvulsive seizures are common during cEEG in critically ill children, especially in those with clinical seizures before cEEG initiation. Patients with PLEDS should be monitored for at least 24 hours to exclude NCSz.