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Somatosensory evoked potential monitoring during cardiac surgery: an examination of brachial plexus dysfunction
D Seal1, J Balaton, S G Coupland
1Department of Anaesthesia, Foothills Hospital, Calgary, Alberta, Canada.
Objective:
To observe the effects of the Favoloro and sternal retractors on the ulnar and median nerve somatosensory evoked potentials (SSEPs) and to identify any relationship with postoperative brachial plexus injury.
Design:
Prospective study.
Setting:
University hospital.
Participants:
Twenty cardiac patients.
Interventions:
SSEPs were studied in patients undergoing cardiac surgery using normothermic cardiopulmonary bypass. Evoked potentials were obtained from bilateral median and ulnar nerves.
Measurements:
The incidence of nerve-specific SSEP changes and their temporal relationship to retractor usage were determined. The overall incidence of SSEP changes was 75%. There were no differences (p > 0.05) between the group showing changes (n = 15) and the group with no changes (n = 5) with respect to age, body surface area, weight, cross-clamp or cardiopulmonary bypass times. There also were no differences (p > 0.05) between the frequencies of left- and right-sided changes, or in nerve-specific SSEP changes. Seventy-four percent of SSEP changes correlated with retractor usage. No SSEP changes were associated with the Favoloro retractor. Significant SSEP depression, assessed by either percentage reduction in amplitude or persistent amplitude reduction, occurred in the absence of postoperative neurological deficits. There were no detected postoperative brachial plexus injuries.
Conclusions:
SSEP changes correlate with the use of the sternal retractor but not the Favoloro retractor. It was not possible to replicate the results of previous investigators in predicting postoperative neurological deficits based on the SSEP changes, and therefore the routine application of SSEP as a monitor cannot be recommended on the basis on these data.