Pain-related middle-latency somatosensory evoked potentials in the prognosis of post anoxic coma: a preliminary report.

Background: Regarding hypoxic-ischemic encephalopathy, while the bilateral absence of N20/P25 somatosensory evoked potentials (SEPs) is considered to be the best indicator of adverse outcomes, the presence of middle latency evoked potentials (MLCEPs) is associated with a favourable neurological prognosis. The main aim of the present study was to investigate whether painful electrical stimulation might be considered a provocative test in producing MLCEPs and predictor of patient's outcomes after cardiac arrest. Methods: Retrospective pilot study. SEPs with and without pain-related electrical stimulation in both median nerves were recorded in 17 patients with post anoxic coma after cardiac arrest. Glasgow Coma Scale, electroencephalograms, heart rate and blood pressure changes were also recorded at the same time. Three months after cardiac arrest the same measures with inclusion of Glasgow Outcome Scale Extended were also performed only in the remaining patients with severe neurological outcome. No one intervention was made. Results: Patients who showed MLCEPs had a good outcome, while patients without N20/P25 SEPs but with increases in blood pressure remained in a vegetative state. Patients who did not show N20/P25 SEPs and increase in blood pressure died within one week. Only one patient who showed N20/P25 SEPs was minimally conscious. Conclusion: These preliminary data suggest that MLCEPs elicited by painful electrical stimulation seem to be a sensitive method to predict the neurological outcome of patients in the acute phase of coma. Blood pressure response might be a prognostic physiological measure of survival in the vegetative state in patients without N20/P25 SEPs.