The prognostic value of three-modality evoked potentials (TMEPs) in anoxic and traumatic comas.

Three-modality evoked potentials (TMEPs) were recorded in 184 comatose patients (52 anoxic, 132 traumatic). Both types of comas were associated with different TMEP patterns. Anoxic comas were associated with prognostically relevant abnormalities of cortical (visual and somatosensory) evoked potentials (EPs), while brainstem (auditory and somatosensory) EPs were not specifically altered. The prognostic value of TMEPs in anoxic comas depended on the time elapsed from the acute episode: mildly altered EPs were associated with a better prognosis in the first 10 days; strongly altered TMEPs were associated with a poorer prognosis from the first day; no definite conclusion could be drawn from mildly altered EPs after the 10th day, or from strongly altered TMEPs in the first 24 h. By contrast, both the cortical and the brain-stem activities were altered in head trauma. The abnormalities were clustered into four patterns: hemispheric damage without brain-stem involvement (pattern 1), mesencephalic lesion (pattern 2), transtentorial herniation (pattern 3), and brain death (pattern 4). Patterns 3 and 4 were uniformly associated with death. The prognostic value of pattern 1 was similar to that observed in anoxic comas. The outcome of patients presenting pattern 2 depended on the extent of hemispheric damage associated with the mesencephalic lesion; we thus suggest to systematically perform magnetic resonance imaging (MRI) in patients presenting TMEP pattern 2. We finally demonstrated that a few patients presenting absent cortical activities in the very acute stage of coma can eventually recover a good neurological function.

[Somatosensory evoked potentials in patients undergoing circulatory arrest under profound hypothermia]. / Le suivi par potentiels évoqués somesthésiques des patients adultes subissant un arrêt circulatoire sous hypothermie profonde.

The surgical repair of ascending aorta aneurysms can only be carried out under total circulatory arrest, and is consequently to be performed under deep hypothermia, in order to adequately decrease the metabolic requirements of the brain. However, the optimal temperature to be reached is poorly known. SEPs to median nerve stimulation were recorded in 21 operations performed in 20 patients undergoing profound hypothermia. The latencies of all SEP components increase to 21 degrees C. Waves N20 and P14 disappear at mean naso-pharyngeal temperatures of 20 degrees C and 17 degrees C, respectively, although a wide inter-individual variability was observed. We suggest to use the P14 disappearance as the criterion to perform the circulatory arrest: in fact, all surviving patients in whom this criterion was fulfilled recovered without any detectable neurological sequellae, while three patients in whom brain activities disappeared independently on body temperature presented with neurological sequellae. Moreover, particularly if patients presenting with ischemia-induced disappearance of Erb's point activities were excluded, we found a significant correlation between the duration of the circulatory arrest and the delay of N20 and P14 reappearance on rewarming. This confirms the importance of sufficient hypothermia, on the one hand; and on the other hand, our findings imply that, even if SEP monitoring considerably decreases the risk of neurological sequellae associated with these operations, the duration of the circulatory arrest should be reduced as far as possible.

Median nerve somatosensory evoked potentials in profound hypothermia for ascending aorta repair.

Median nerve somatosensory evoked potentials (SEPs) were recorded in 9 patients undergoing profound hypothermia for surgical repair of the aortic arch. In addition to the known increase in peak latencies, hypothermia gave rise to the appearance of peaks ('P13,' 'N14') inconsistently recognized at normothermia; moreover, profound hypothermia is associated with the disappearance of cortical activities around 20 degrees, of subcortical waves at lower temperatures. The practical implications of the results are 3-fold: firstly, they suggest that the 'P13' and P14 should both be intracranially generated, at a pre- and postsynaptic level with respect to the cuneate nucleus, respectively; secondly, they show that some discrepancies between previous papers dealing with SEPs and hypothermia can be explained by differences in the choice of the reference; thirdly, they bring some suggestions on a better use of SEPs to monitor patients undergoing aortic arch surgery.