Is the auditory brain-stem response (ABR) effective in the assessment of post-traumatic coma?

The aim of the present study is to evaluate the capacity of ABRs to detect the limit between reversible dysfunction and irreversible damage to the brain-stem after severe head injuries. ABRs were recorded in 40 severely head-injured patients, strictly selected on the basis of clinical and CT scan findings and the absence of otologic disease. The interpeak latency of waves V-I (IPL V-I) was calculated and compared to that recorded in 19 healthy control subjects. The distribution curve for IPL V-I in surviving patients was analysed. The overall mortality was 47.5%; all the patients showing an IPL V-I greater than 4.48 msec died or remained vegetative, while all but 2 of the patients with IPL V-I less than 4.48 msec survived. The IPL V-I was significantly different from normal value in surviving patients, showing a brain-stem dysfunction in reversible post-traumatic coma. The 95% confidence limits for the mean IPL V-I in the surviving population were 4.08 and 4.24 msec. Our results confirm the high prognostic accuracy of ABR (P less than 0.001) and suggest the hypothesis that 95% of survivors have an IPL V-I ranging between 3.82 and 4.50 msec.