Serial recordings of auditory brainstem responses in severe head injury: relationship between test timing and prognostic power.

ABRs have proved to be very accurate prognostic indicators in severe head injury, even when predictions are based on single ABR recordings. In this study we submitted 30 severely head-injured patients to serial ABR recordings (during the clinical course of posttraumatic coma) in order to verify whether the ABR prognostic power may depend on test timing in relation to the injury. 15 patients (50%) died, 5 (16.7%) remained vegetative, 2 (6.6%) severely disabled and 8 (26.7%) recovered. All recovered patients had normal ABR throughout clinical course, while severely disabled and vegetative patients showed at least transently ABR abnormalities (namely, an interpeak latency of waves V-I greater than 4.48 ms). Among dead patients, 8 showed steady and 3 transient ABR abnormalities during the clinical course, while 2 of 3 patients with normal ABR dead from extracranial complications. ABRs were significantly related to the outcome at any time, but gave more accurate prognostic indications on days 3-6 after the injury. The use of serial ABR recordings appeared to improve the outcome predictions in comparison with single ABR tests. Finally our result confirm the previously reported existance of a breakpoint between reversible brainstem dysfunction and irreversible brainstem damage defined by an IPL V-I of about 4.50 ms.