Reply to Letter: "Outcome prediction in postanoxic coma with electroencephalography: the sooner the better"

The prerequisite for starting the prognostication process is the absence of consciousness assessed using clinical examination, which is usually not reliable before 72h or more from ROSC. The majority of patients destined to a good outcome will awake within 72h-96h from cardiac arrest. Consequently, prognostication is appropriate in patients who remain comatose after that time point. Results of predictors evaluated earlier should be considered only after a reliable clinical examination can be made. When assessing prognosis, we recommended that the most robust predictors should be used first. These include the absence of either ocular reflexes (pupillary light response and corneal reflex) or the N20 wave of short-latency somatosensory evoked potentials (SSEPs). These predictors have given consistent results in more than five independent studies and have high precision (95%CI for false positive rate below 5%). Unfortunately, the current evidence supporting the use of EEG as a predictor of poor outcome is much less robust. In particular, predictors based on electrophysiology are often inaccurate during the first 24-48h after ROSC, mainly because of interference from both low body temperature and drugs used to maintain it. Even SSEPs, which are considered to be more resistant than EEG to these confounders, may give falsely pessimistic predictions when recorded during hypothermia treatment.