Somatosensory evoked potential monitoring during cardiac surgery: an examination of brachial plexus dysfunction

Evoked Potentials during Cardiac and Major Vascular Operations

Somatosensory evoked potentials are widely used in spine surgery to prevent injury to the spinal cord. However, their application in cardiac and major vascular surgery is largely unappreciated. This paper will review the unique stresses placed on peripheral nerves, spinal cord, and brain during these operations. In addition, the potential benefits of perioperative somatosensory evoked potentials monitoring are described in detail.

Does retraction of the sternum during median sternotomy result in brachial plexus injuries?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was 'does retraction of the sternum during median sternotomy result in brachial plexus injuries or peripheral neuropathies?' Altogether 58 papers were found using the reported search, of which 12 represented the best evidence to answer the question. The authors, date, journal and country of publication, patient group studied, study type, relevant outcomes and results of these papers were tabulated. Caudal placement of the retractor or relieving the pressure superiorly by removing the upper blades of a retractor (P = 0.02) and use of a caudally placed symmetrical retractor has been shown to reduce neuropathy. Positioning of the patient with 'hands up' positioning showed significant reduction in the incidence of brachial plexus injuries. Furthermore, how wide the retractor is opened and use of an asymmetrical retractor for internal mammary artery (IMA) harvesting are also important factors in quantifying risk of postoperative neuropathy. Wider sternal retraction and longer bypass time did increase the risk of developing postoperative neuropathy. Three asymmetrical retractors were looked at that demonstrates the Delacroix-Chevalier to be the safest (P < 0.05). We conclude that median sternotomy risks brachial plexus injury and where possible the sternum should be opened as small a distance as possible with symmetrical retractor and using a caudally placed retractor.

Neurophysiological identification of position-induced neurologic injury during anterior cervical spine surgery

This study was a retrospective review of 3,806 patients who underwent anterior cervical spine surgery with multi-modality neurophysiological monitoring consisting of transcranial electric motor evoked potentials, somatosensory evoked potentials and spontaneous electromyography between 1999-2003. The objectives of this study were twofold: (1) to evaluate the role of transcranial electric motor evoked potential tceMEP and ulnar nerve somatosensory evoked potential (SSEP) monitoring for identifying impending position-related stretch brachial plexopathy, peripheral nerve entrapment/compression or spinal cord compression and (2) to estimate the point-prevalence of impending neurologic injury secondary to surgical positioning effects. Sixty-nine of 3,806 patients (1.8% showed intraoperative evidence of impending neurologic injury secondary to positioning, prompting interventional repositioning of the patient. The brachial plexus was the site of evolving injury in 65% of these 69 cases. Impending brachial plexopathy was most commonly noted immediately following shoulder taping and the application of counter-traction. Brachial plexus stretch upon neck extension for optimal surgical access and visualization was second in frequency-of-occurrence. Evolving traction injury to the ulnar nerve attributed to tightly-wrapped or malpositioned arms was observed in 16% of alerted cases, whereas evolving spinal cord injury following neck extension accounted for an additional 19%. This study highlights the role of tceMEP and ulnar nerve SSEP monitoring for detecting emerging peripheral nerve injury secondary to positioning in preparation for and during anterior cervical spine surgery.

Somatosensory evoked potential monitoring used to compare the effect of three asymmetric sternal retractors on brachial plexus function

We compared the effect of three different asymmetric sternal retractors on brachial plexus dysfunction using intraoperative somatosensory evoked potentials (SSEPs). We studied 60 patients undergoing coronary bypass and internal mammary harvest. Assessment of brachial plexus function was performed pre- and postoperatively. Patients were assigned the use of a Pittman (MN Scientific Instruments Inc., Minneapolis, MN), Rultract (Rultract Inc., Cleveland, OH), or Delacroix-Chevalier (Delacroix-Chevalier, Paris, France) asymmetric sternal retractor for internal mammary exposure. SSEP changes from baseline during asymmetric retractor use and removal were determined, and average changes were compared among the retractor groups. Patient demographics and baseline SSEP values were similar. Fewer patients in the Delacroix-Chevalier group had decreases in SSEP amplitudes after retractor placement. Of the patients in the Rultract and Pittman groups, 45% and 25%, respectively, had amplitude decreases of >50%, compared with only 5% of the Delacroix-Chevalier patients. Three patients in both the Pittman and Rultract groups and one patient in the Delacroix-Chevalier group suffered brachial plexus symptoms postoperatively. We conclude that the Delacroix-Chevalier retractor is associated with less neurophysiologic evidence of brachial plexus dysfunction during asymmetric sternal retraction compared with either the Pittman or Rultract sternal retractors.

IMPLICATIONS

We used somatosensory evoked potentials to assess the effect of several different asymmetric sternal retractors on brachial plexus dysfunction and to determine which produced the least evidence of nerve damage during surgical exposure of the internal mammary artery.