Nasopharyngeal electrode recording of somatosensory evoked potentials as an indicator in brain death.
Median nerve somatosensory evoked potentials were recorded in 28 comatose patients, eight of whom were progressing from coma to eventual brain death and in 11 brain dead patients using electrodes over the scalp, neck and nasopharynx (nasopharyngeal electrode). This recording technique was used to assess the different derivation of brainstem P14 wave activity. It showed that in the midfrontal scalp to the nasopharynx derivation a clear P14 was present in all comatose patients. This component disappeared during the passage from coma to brain death. In a separate group, simultaneous direct recordings in the vicinity of the dorsal column nuclei and with a nasopharyngeal electrode were made in five patients undergoing neurosurgical procedures at the craniocervical junction with the same somatosensory evoked potential monitor. We found that the P14 recorded with the nasopharyngeal electrode in the neurosurgical patients corresponded in latency and morphology with the P14 recorded directly on the surface of the craniocervical junction and more specifically in the vicinity of the nucleus cuneatus. The nasopharyngeal electrode provides non-invasive access to the ventral brainstem at the medullo-pontine level and the disappearance of the P14 shows a clear sign of involvement of the craniocervical junction in brain dead patients. Our study showed that with a simple montage the nasopharyngeal electrode is an effective non-invasive monitor for brainstem activity and can be used as an early diagnostic indicator of brainstem death.