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Objective: To study the event related potentials (ERPs) in coma and altered states of consciousness, their relationship with the clinical status and coma outcome., Methods: ERPs were recorded with a passive auditory oddball paradigm in 103 patients. Their probability of occurrence and the peak latencies and amplitudes were studied as a function of the Glasgow Coma Score (GCS). Their relationship with outcome was studied in a subset of 83 patients examined within the first 4 days, and expressed in terms of sensitivity, specificity, and negative or positive prognostic values., Results: When present, the ERPs to rare stimuli consisted of a fronto-central negativity (N(endog), mean latency: 330 ms) and a fronto-central positivity (P(endog), mean latency: 431 ms) following the exogenous N100-P200 complex. Both their probability of occurrence and their latencies and amplitudes were related with the GCS in anoxic and traumatic comas. The N(endog) and P(endog) had high sensitivity with a negative predictive value of 70% and 100%, respectively, but a low specificity, with a positive predictive value of 44% and 41%, respectively., Conclusions: ERPs can be recorded in some comatose patients and are likely to reflect implicit orienting processes rather than preserved consciousness. Their presence implies a good prognosis but no conclusion can be drawn from their absence.

Background: We evaluate the efficiency of multilevel somatosensory evoked potential (SEP) monitoring for intraoperative re-establishment of blood flow to the spinal cord in 63 patients undergoing descending aorta repair., Methods: The presence of critical vessels in a cross-clamped aortic segment was ascertained by a 15 minute SEP observation period while the segment between the clamps was vented to drain out the collateral flow., Results: SEPs influenced the surgical strategy in 17 cases (27%): use of the Biomedicus in 1 traumatic rupture; critical vessel reimplantation or distal clamp replacement in 13 cases of segmental spinal ischemia; and hastening the procedure or proximal clamp replacement in 3 cases of left carotid ischemia. There were no cases of unexplained multilevel SEP abnormalities. Immediate paraplegia was observed in 2 cases (1 pre-existing; 1 forecast by a 199-minute period of SEP absence due to segmental ischemia); 2 patients presented delayed paraplegias despite unchanged intraoperative SEPs, and 1 case presented a transient paraplegia due to lower motoneuronal involvement., Conclusions: SEPs efficiently identified critical vessels to be reimplanted in order to avoid immediate paraplegia. However, systematic additional vessel reimplantation, if technically feasible, and prolongation of SEP monitoring during the postoperative period with careful blood pressure control are needed to prevent delayed paraplegia.

This paper presents the results of intraoperative median nerve SEP monitoring in 205 successive patients undergoing isolated carotid endarterectomy (CE) (N = 172) or CE followed by coronary bypass (CBP) and/or vascular replacement (VR) (N = 33). The left and right median nerves were alternately stimulated and recordings performed on 4 channels: cervical, ipsi- and contralateral parietal, and frontal. SEPs were qualitatively rated in terms of mild, moderate, or severe ipsilateral, contralateral, or bilateral abnormalities. The SEP abnormalities were subdivided into 5 categories as a function of their relationships with intraoperative events: no alterations (67.3%), early or late SEP alterations after carotid cross-clamping (15.6%), SEP alterations after a drop in blood pressure (occurring outside of or within the cross-clamping period) (15.1%), SEP alterations of a most likely embolic origin (2.4%), SEP changes after head positioning (1%), and SEP changes after a modification of the anesthetic regimen (1.5%). Only moderate to severe SEP alterations occurring soon after carotid cross-clamping justified shunt installation in 16% of the cases. SEP alterations after a drop in blood pressure were reversed merely by restoring blood pressure. The neurological outcome was uneventful in 94.2% of cases. Of the 12 patients who developed neurological sequellae, only one case presented transient sequellae after isolated CE without SEP changes while most cases either had undergone combined CE and CBP and/or VR (6 cases) or had presented SEP alterations of embolic origin (3 cases). We conclude that our system of qualitative rating of SEPs proved very sensitive to intraoperative hemodynamic disturbances or macroembolisms.

This paper compares the respective yields of our SEP scoring system ('qualitative' criteria), based on the subdivision of SEP abnormalities into mild, moderate, and severe abnormalities, and a quantitative one ('classical' criteria), based on a more than 1 ms CCT increase or 50% decrease of N20 amplitude, for the detection of brain ischemia justifying shunt placement during carotid endarterectomy (CE). For that purpose, we examine the sensitivities of several neurophysiological parameters (the ipsilateral and contralateral CCT, the amplitudes of the ipsilateral and contralateral frontal and parietal SEPs) to carotid cross-clamping or to a drop of blood pressure. Our data first confirm that shunted patients developed a CCT increase and a decrease of N20 amplitude on the ipsilateral hemisphere. They further demonstrate that 50% of the patients who were immediately shunted on the basis of qualitative criteria would not have been shunted or would have been shunted with a longer delay on the basis of quantitative criteria. Simultaneously, the overall percentage of shunted patients was not significantly higher than in studies using the 'classical' criteria. Thus, it was hard to decide between the 'qualitative' and the 'classical' criteria on the basis of patient data. However, our 'qualitative' system appears advantageous in that it smooths out the influence of factors liable to interfere with the quantitative parameters.

This study examines how the recording of the lumbar and subcortical components of the posterior tibial nerve (PTN) SEPs may usefully replace that of cortical components in situations in which these components cannot be reliably obtained (infants, high concentrations of halogenated gasses). Lumbar, brain-stem, and cortical PTN SEPs were intraoperatively monitored in 7 patients undergoing repair of aortic coarctation under variable isoflurane concentration (up to 1.2%). Four patients were less than 1 year old. Two distinct activities were evidenced at the lumbar level in all of the patients: the dorsal root component (DRC) and the dorsal horn negativity (DHN). The equivalent of the adult P30 (lemniscal positivity; LP) was also present in all of the patients, whatever their age or the concentration of isoflurane. By contrast, the parietal activities were absent intraoperatively in the youngest patients. Spinal-cord ischemia consecutive to aortic cross-clamping gave rise to early DHN changes and later alterations of the LP in the two patients in which it occurred, while the DRC and the peripheral nerve activities remained unchanged. This elective sensitivity of the DHN is likely due to it being dependent on the gray matter of the spinal cord, the basal metabolism of which is greater than that of the white matter and to the situation of the DHN generator in a watershed zone of the spinal cord. This study emphasizes the interest of PTN SEPs for spinal-cord monitoring in vascular surgery and the importance of combining the recording of parietal activities with that of the lumbar spinal components.