Somatosensory evoked potential monitoring of the brachial plexus to predict nerve injury during internal mammary artery harvest: intraoperative comparisons of the Rultract and Pittman sternal retractors.

Brachial plexus injury after coronary artery bypass grafting (CABG) continues to be a common problem postoperatively. With the use of somatosensory evoked potential monitoring (SSEP), neurologic integrity of the brachial plexus during internal mammary artery (IMA) harvest was assessed and the Rultract and Pittman sternal retractors were compared to determine what effect they had on SSEP characteristics. Results showed that the Rultract and Pittman retractors caused large decreases in SSEP amplitudes after insertion, (1.25 +/- 0.14 versus 0.72 +/- 0.09, P < 0.05; and 1.64 +/- 0.27 versus 0.91 +/- 0.14, P < 0.05) respectively. This decrease was noted in 85% of Rultract and 68.75% of Pittman patients, respectively. Amplitudes increased after retractor removal but never returned to baseline values. Cooley retractor placement in the patients not undergoing IMA harvest (control) produced only mild decreases in amplitude. Waveform latency increased in all groups after retractor placement, but these increases were thought to be clinically insignificant. Postoperatively, three patients in each of the IMA retractor groups had brachial plexus symptoms (18%), whereas only one patient in the control group had symptoms. Somatosensory evoked potential monitoring seems to be a sensitive intraoperative monitor for assessing brachial plexus injury during CABG. The nerve plexus seems to be most at risk for pathologic injury during retraction of the sternum for IMA harvest. Though the Rultract retractor caused greater changes in SSEP characteristics than the Pittman, no clinical outcome differences between the two could be ascertained. Using SSEP monitoring may reduce brachial plexus injury during IMA harvest by allowing early detection of nerve compromise and therapeutic interventions to alleviate the insult while under general anesthesia.