Electroencephalographic monitoring during hypothermia after pediatric cardiac arrest

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Abstract
Background: Hypoxic ischemic brain injury secondary to pediatric cardiac arrest (CA) may result in acute symptomatic seizures. A high proportion of seizures may be nonconvulsive, so accurate diagnosis requires continuous EEG monitoring. We aimed to determine the safety and feasibility of long-term EEG monitoring, to describe electroencephalographic background and seizure characteristics, and to identify background features predictive of seizures in children undergoing therapeutic hypothermia (TH) after CA. Methods: Nineteen children underwent TH after CA. Continuous EEG monitoring was performed during hypothermia (24 hours), rewarming (12–24 hours), and then an additional 24 hours of normothermia. The tolerability of these prolonged studies and the EEG background classification and seizure characteristics were described in a standardized manner. Results: No complications of EEG monitoring were reported or observed. Electrographic seizures occurred in 47% (9/19), and 32% (6/19) developed status epilepticus. Seizures were nonconvulsive in 67% (6/9) and electrographically generalized in 78% (7/9). Seizures commenced during the late hypothermic or rewarming periods (8/9). Factors predictive of electrographic seizures were burst suppression or excessively discontinuous EEG background patterns, interictal epileptiform discharges, or an absence of the expected pharmacologically induced beta activity. Background features evolved over time. Patients with slowing and attenuation tended to improve, whereas those with burst suppression tended to worsen. Conclusions: EEG monitoring in children undergoing therapeutic hypothermia after cardiac arrest is safe and feasible. Electrographic seizures and status epilepticus are common in this setting but are often not detectable by clinical observation alone. The EEG background often evolves over time, with milder abnormalities improving and more severe abnormalities worsening. BS = burst suppression; CA = cardiac arrest; CPR = cardiopulmonary resuscitation; DD = developmental delay; FEN = fentanyl; FOS = fosphenytoin; HIE = hypoxic ischemic encephalopathy; LEV = levetiracetam; LZP = lorazepam; MDZ = midazolam; NCS = nonconvulsive seizures; NCSE = nonconvulsive status epilepticus; NPV = negative predictive value; PB = phenobarbital; PED = periodic epileptiform discharge; PICU = pediatric intensive care unit; PPV = positive predictive value; SE = status epilepticus; SIDS = sudden infant death syndrome; sz = seizures; TH = therapeutic hypothermia; VEC = vecuronium; VPA = valproic acid; VT = ventricular tachycardia.

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