Effect of mild hypothermic cardiopulmonary bypass on the amplitude of somatosensory-evoked potentials.
BACKGROUND
Several neurophysiological techniques are used to intraoperatively assess cerebral functioning during surgery and intensive care, but the introduction of hypothermia as a means of intraoperative neuroprotection has brought their reliability into question. The present study aimed to evaluate the effect of mild hypothermia on somatosensory-evoked potentials' (SSEPs) amplitude and latency in a cohort of cardiopulmonary bypass (CPB) patients as the temperature reached the steady-state.


METHODS
The amplitude and latency of 4 different SSEP signals--N9, N13, P14/N18 interpeak, and N20/P25--were evaluated retrospectively in 84 patients undergoing CPB during normothermic (36°C±0.43°C) and mild hypothermic (32°C±1.38°C) conditions. SSEPs were recorded in normothermia immediately after the induction of anesthesia and in hypothermia as the temperature reached its steady-state, specifically, when the nasopharyngeal temperature was equivalent to the rectal temperature (±0.5°C). A paired-samples t test was performed for each SSEP to test the differences in latencies and amplitudes between normothermic and hypothermic conditions.


RESULTS
Compared with normothermia, hypothermia not only significantly increased the latency of all SSEPs, N9 (P<0.001), N13 (P<0.001), P14/N18 (P<0.001), and N20/P25 (P<0.001), but also the amplitude of N9 (P<0.001) and N20/P25 (P<0.001).


CONCLUSIONS
The increased amplitude in particularly of cortical SSEPs (N20/P25), detected specifically during steady-state hypothermia, seems to support the clinical utility of this methodology in monitoring the brain function not only during cardiac surgery with CPB, but also in other settings like therapeutic hypothermia procedures in an intensive care unit.
*Department of Anesthesia and Intensive Care †Neuromonitoring Project, Department of Anesthesia and Intensive Care ∥Departement of Cardiovascular Disease §Department of Neurosurgery, Treviso Regional Hospital, University of Padova, Padova ‡Department of Anesthesia and Intensive Care, Rovigo Regional Hospital, Rovigo, Italy ¶Department of Neuroscience, Winthrop University Hospital, NY.
Paolo
P
Zanatta
Enrico
E
Bosco
Alessandra
A
Comin
Anna Paola
AP
Mazzarolo
Piero
P
Di Pasquale
Alessandro
A
Forti
Pierluigi
P
Longatti
Elvio
E
Polesel
Mark
M
Stecker
Carlo
C
Sorbara
D000768:Anesthesia, General; D001831:Body Temperature; D002315:Cardiopulmonary Bypass / Q000379:methods*; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D007036:Hypothermia, Induced / Q000379:methods*