I. J. Behr1, S. Mansoor1, M. McLeod1 1Michigan State University,Surgery,Lansing, M, USA
Introduction:
Surgical injury to the recurrent laryngeal nerve (RLN) is a feared complication of head and neck surgery due to potential for significant permanent functional disability. Originally recommended by Lahey, intra-operative identification and protection of the nerve, remains the gold standard for minimizing RLN injury. Over time, less invasive monitoring systems and methods to protect the RLN during surgical procedures have developed. One such method is the endotracheal Nerve Integrity Monitoring (NIM) system. This study demonstrates a novel method to more accurately ensure placement of the NIMS device.
Methods:
176 patients were enrolled in this prospective clinical trial. Each patient underwent surgery involving dissection around the recurrent laryngeal nerve thus requiring monitoring. These surgeries included partial thyroidectomy, near total thyroidectomy, and total thyroidectomy. All patients were placed under general anesthesia and intubated with a NIMs endotracheal device.
All patients had both the tap test and the train of 4 stimulation performed prior to beginning surgery. The results were determined from recordings through the NIMs monitoring system.
The tap test was performed by percussion to the midline trachea and recording the results through the NIMs device. The train of 4 was performed by the anesthesia team with 2 electrical pads placed over the facial musculature. A train of 4 stimulation was created with a electrical stimulator and the results were recorded through the NIMs device.
The most accurate method to ensure placement is by direct stimulation/contraction of the vocal cords through stimulation of the vagus nerve. 3 of the 176 patients consented to direct stimulation of the vagus nerve as a control study. This was done by opening the carotid sheath, freeing a small 1cm section of the nerve from the surrounding tissue and directly stimulating the nerve. The results of this test were also recorded through the NIMs device.
Results:
Out of 176 patients 131 were found to have adequate positioning using the tap test (74.4%). With a train of 4 stimulation 170/176 (96.6%) were found to have accurate positioning. Using the McNemar test, train of four peripheral nerve stimulation showed significantly more positive findings than the tap test , p < 0.001
Conclusion:
This clinical prospective study of 176 patients showed a novel method to determine accurate positioning of the NIM device using a train of four electric stimulation. By causing contraction of the musculature and vocal cords overlying the NIMs device more accurate placement was established compared to a less accurate but commonly used method of simply tapping the larynx (p < 0.001). This minimally invasive and improved method to determine accurate positioning of the NIMs device could therefore minimize the risk of RLN injury.