Significance of Electrophysiologic Studies in Brain Hypothermia

Summary

To evaluate the significance of an electrophysiologic monitoring system during brain hypothermia, we measured the brainstem auditory evoked potentials (BAEPs), somatosensory evoked potentials (SEPs), and topographic electroencephalography (EEG) in 29 critically ill patients (15 with severe head injury and 14 with encephalopathy following cardiopulmonary resuscitation). When the temperature measured in the internal jugular vein fell from 36°C to 33°C, the prolongation of latency in BAEPs was 0.1 ± 0.06 ms in wave I, 0.5 ± 0.23 ms in wave III, and 0.92 ± 0.86 ms in wave V. In addition, the prolongation of latency in SEPs was 1.2 ± 0.2 ms in N13 and 2.1 ± 0.4 ms in N20. The bifrontal fast wave responses, except for those of primary injured lesions, in the topographic EEG were recognized in 9 of 13 patients within 30 min after the injection of midazolam which was used as a sedative. When the temperature fell from 36°C to 33°C, the ratio of the delta and theta waves to the alpha waves recorded from 12 scalp electrodes increased. An electrophysiologic evaluation in critically ill patients should thus be considered an effective real-time monitoring system in patients experiencing brain hypothermia.