Somatosensory and brainstem auditory evoked potentials in cardiac arrest patients treated with hypothermia*

Advances in emergency medi-cine have increased the num-ber of cardiac arrest patients inthe emergency department. The duration and severity of global cere-bral ischemia and secondary mechanisms of ischemia related to reperfusion con-tribute to the extent of brain damage. Mild hypothermia of 33°C for 12 or 24 hrs has been shown to improve neurologic outcome after cardiac arrest (1, 2) and also to increase the chance of survival (1). Early prediction of neurologic outcome for patients resuscitated from cardiac arrest is a challenging task. The median nerve somatosensory evoked potentials (SEPs) have been reported to accurately predict poor outcome after cardiac arrest (3, 4). Hypothermia is known to prolong all neu-ronal conduction velocities, including the SEP and brainstem auditory evoked poten-tial (BAEP) latencies, and temperature has also been reported to affect the amplitudes of SEP responses (5–8). Mild to moderate hypothermia does not abolish cortical re-sponses to sensory evoked potentials (9). The cortically generated component N20 has been shown to disappear only at mean nasopharyngeal temperature of 20°C under normal hemodynamic conditions (6, 10). The measurement of BAEPs has been used to monitor neuronal function at the level of the brainstem. Hypothermia increases the BAEP interwave latencies (5, 11, 12). BAEP components have also been reported to be abolished at temperatures below 20°C (12). The aim of this study was to evaluate the prognostic value of the short-latency median nerve SEPs and BAEPs in out-come prediction for comatose cardiac ar-rest patients treated with hypothermia. SUBJECTS AND METHODS The protocol and consent procedure of this study was approved by the ethics committee of Helsinki University Central Hospital in accor-dance with institutional guidelines. A deferred consent was used for all patients. The patient’s family was informed about the trial and could withdraw the patient at any time from the study. Each patient was informed about the trial both orally and in writing, when he or she was able to receive this information. Patients randomized into the Hypothermia After Cardiac Arrest trial were included (1). All adult patients admitted to the emergency de