The role of EEG after cardiac arrest and hypothermia.

Commentary Despite decades of research, the exact role of EEG in predicting and improving outcomes in survivors of cardiac arrest (CA) remains a hot topic of discussion. Here are the facts: Since the 1960s, EEG has become an integral part of prognos-tication after CA (1). In 2002, two randomized clinical trials documented the benefits of mild therapeutic hypothermia (TH) in comatose survivors of CA, improving neurologic outcomes and survival (2). In 2005, the American Heart Association recommended TH as a standard of care (3), and in 2006, the American Academy of Neurology (AAN) formalized outcome prediction in comatose survivors, after cardiopul-monary resuscitation, through practice guidelines (4). So, on the surface, we have an effective treatment and " officially endorsed " guidelines for using various tools, including EEG, in prognostication. Here is the catch: despite TH, almost half of patients still do poorly after CA, and all the data driving the AAN guidelines were generated before the routine implementation of TH. Yet, many prognostication criteria are potentially affected by TH. A recent prospective study showed a higher rate of false positive rate (FPR) mortality predictions using incomplete recovery of brainstem reflexes (4% FPR), myoclonus (3% FPR), and absent motor response to pain (24% FPR) in the TH population compared with CA survivors from the pre-TH era (0% FPR for all these variables) (5). The door then remains open for work like the study by Crepeau et al., chosen for this commentary, to evaluate the current role of EEG. Where Do We Stand Now? First, EEG Findings Remain Highly Predictive of Neurologic Outcome After the Routine Implementation of TH. The study at hand classifies the " traditional malignant " EEG findings of burst suppression, low-voltage output pattern, alpha/theta coma, focal or generalized seizures, generalized periodic epileptiform discharges, status epilepticus, and background unreactivity into a " grade 3 " or " severe " abnormality. Eighty-nine percent of patients with grade 3 abnormality during TH and all those who had it during subsequent normo-thermia had a poor neurologic outcome (high specificity). Conversely , 76% of patients with a poor outcome had a grade 3 abnormality (high sensitivity). All the patients with mild (grade 1) abnormalities as defined by excessive beta, theta slowing, or anesthetic pattern during TH or normothermia recovered with no to moderate disability. This and other grading systems (1, 6) offer reasonable accuracy but require the clinician to remember the individual classification. …