[Experimental study of the usefulness of evoked potentials in predicting the reversibility of the brainstem function following infratentorial epidural balloon compression].

With few warnings signs, posterior fossa mass lesions can affect life-supporting brainstem systems directly and cause a precipitous failure of vital functions. Consequently, a technique, by which brainstem dysfunction could be detected at its reversible stage, would have clinical value. Recently manly reports have suggested that the evoked potentials might be advantageous in assessing a developing brainstem dysfunction and might be a more sensitive or reliable detector of deteriorating neurological function than the physical or neurological signs. To explore this possibility, we recorded somatosensory evoked potentials (SEP) and brainstem auditory evoked potentials (BAEP) serially during inflation and deflation of balloons placed in the suboccipital epidural space of cats, as a model of an acutely expanding posterior fossa lesion. The results were correlated simultaneously recorded cardiovascular and pupillary function and with supratentorial and infratentorial epidural pressure. In this study, N1 of cortical SEP (CSEP), wave IV of BAEP, and wave III of short latency SEP (SSEP) were found to be useful parameters in predicting the electrophysiological reversibility. Experimental results were as follows: 1) As the infratentorial epidural balloon was expanded, CSEP, wave IV of BAEP and wave III of SSEP showed remarkable changes both in latency and in amplitude. Decrease in blood pressure and pulse rate preceded or developed at the same time as the apparent change in CSEP. Futher expansion of the balloon resulted in Cushing phenomenon and lability of blood pressure.2) As long as wave IV of BAEP remained, and decompression was started within 15 minutes after N1 of CSEP were completely suppressed, changes in SEP. BAEP and cardiovascular function were all reversible.2+ decompression. (ABSTRACT TRUNCATED AT 250 WORDS)