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.
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.
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).
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
This work was conducted at the Department of Anesthesia and Intensive Care and Cardiovascular Diseases of Treviso Regional Hospital, Italy.
Funding for this study was provided by Regione Veneto, Italy, for a project on the reduction of neurodysfunction after cardiac surgery and neurosurgery and improvement in multimodality neuromonitoring for neurophysiological technicians and psychologists. This study was also carried out with a grant by the Veneto Banca Foundation of Treviso for a psychologist.
The authors have no conflicts of interest to disclose.
Reprints: Paolo Zanatta, MD, Department of Anesthesia and Intensive Care, Treviso Regional Hospital, Azienda Ospedaliera Ulss 9, Piazzale Ospedale 1, Treviso 31100, Italy (e-mail: email@example.com).
Received April 22, 2013
Accepted August 26, 2013