Compound Muscle Action Potentials (CMAP) for Postoperative Monitoring of Functioning Free Muscle Transfer

Abstract

For successful functional reconstruction using functioning free muscle transfer (FFMT), complete survival of the transferred tissue is essential. However, muscle tolerates a shorter period of ischemia than other tissues such as skin and bone. Therefore, the use of skin flaps as a monitoring tool cannot sensitively reflect the vascularity of FFMT, and may result in delayed detection of vascular compromise, leading to muscle necrosis with an intact skin flap. In order to obtain effective results with FFMT, early detection of vascular compromise is important. We here report the use of compound muscle action potentials (CMAP) as a supplemental method in the monitoring of free gracilis transfer. A sudden 50% decrease in CMAP amplitude within 1 hour is an indication for revision surgery. Between 2007 and 2017, we performed 188 FFMT procedures for brachial plexus injury reconstruction. Eight cases had vascular compromise. All cases salvaged by CMAP monitoring had a shorter ischemic time than with conventional skin flap monitoring. This technique is most useful for postoperative vascular monitoring of a buried muscle flap.