Continuous EEG in Management of Postanoxic Epilepsy in Cardiac Arrest Survivors Undergoing Therapeutic Hypothermia Therapy: Editorial Commentary on Westhall et al. ( 2013 )

Therapeutic hypothermia in select cardiac arrest survivors has become standard of care and has been shown to be associated with improved neurologic and survival outcomes (Bernard et al., 2002; Holzer, 2002; Kim et al., 2011). One of the complications seen in post–cardiac arrest patients is the evolution of seizure activity. Their prognostic significance in these patients is still not clear. The incidence of convulsive and nonconvulsive seizures, including status epilepticus, has been stated to be between 15 and 44% in various studies (Rossetti et al., 2010; Mani et al., 2012; Rittenberger et al., 2012). The occurrence of status epilepticus has been shown to be associated with increased morbidity and mortality (Krumholz et al., 1988). This holds true for cardiac arrest patients in the pre-TH era as well as those presently treated with TH (Wijdicks et al., 2006; Abend et al., 2009). However, there are case studies of patients making good recovery after myoclonic status epilepticus (Rossetti et al., 2009). Thus it remains unclear whether early diagnosis and effective management of seizures can improve prognosis in cardiac arrest survivors undergoing TH.

The clinical diagnosis of seizures in patients undergoing TH post–cardiac arrest is challenging because seizures can be either nonconvulsive or masked by concomitant use of paralytics. Moreover, the use of routine anti-epileptics in these patients may not be fully effective because of either the severity of neurologic injury or the altered potency of these agents in the presence of hypothermia (Tortorici, 2007).

Studies have shown that between 33 and 56% of cardiac arrest survivors have seizures in the cooling phase (Mani, 2012). It has been shown that the longer one waits to initiate treatment of seizures the more difficult it is to control (Shorvon, 2011). Moreover, the duration of uncontrolled seizures is associated with worse prognosis (Towne, 1994). So it is essential that seizures be diagnosed early on, and a neurology consultation should not wait till the patients are rewarmed.

Routine electroencephalography can detect seizures in comatose patients but the rate is low (Towne, 2000). Recent studies have shown that in various high risk patients the use of continuous electroencephalography (cEEG) can increase detection of seizures up to 48%, and a significant number of these are nonconvulsive (Hirsch, 2010).

Westhall et al. (2013) have presented an interesting case of postanoxic status epilepticus that was successfully treated with the use of cEEG monitoring. The patient report presented has several interesting features. First, although there were good prognostic factors early on (ventricular fibrillation cardiac arrest as compared to nonshockable rhythm, localization of painful stimuli by the patient, and improved level of consciousness post-TH), the patient developed late- status epilepticus. Second, there was a delay in the diagnosis of the patient's status epilepticus due to the absence of convulsions in the presence of heavy sedation. Third, multimodality prognostication utilizing serum enolase level, cortical N20 potentials, and brain magnetic resonance study proved accurate. Fourth and most importantly, the detection and effective management of the patient's status epilepticus was only possible because of the use of cEEG monitoring.

The case report by Westhall et al. (2013) illustrates the importance of utilizing cEEG monitoring early on in all cardiac arrest survivors undergoing TH. However, it must be noted that presently cEEG is resource-intensive and is not available at all institutions performing TH. Whether the routine practice of cEEG monitoring in all cardiac arrest survivors undergoing TH will improve outcomes and should become a standard of care will need further study in the form of well-designed clinical trials.