Clinical Application of "Train of Four" Testing in the Intraoperative Monitoring Setting

Overview

The study examines the clinical application of TOF (train of four test) used by anesthesiologists and neurophysiologists during instrumented spine procedures, as well as certain associated parameters. 'Train of four' test is a test routinely used during the surgery, which is performed by stimulation of peripheral nerve with purpose to determine the degree of muscle relaxation by interpretation of muscle response. During spine surgery, it is helpful for the surgeon to have a patient's muscles as relaxed as possible with the least amount of tone, especially when exposing. Anesthesiologists achieve this level of relaxation by giving a neuromuscular blocking agent. If medication given to do this has not fully left their system by the time the surgeon needs to start putting in the screws and rods, then the intraoperative monitoring can not be adequately performed. If the muscles are too relaxed, then free run EMG and screw stimulation, two monitoring methods used, will not be analyzed correctly and the surgery may be adversely affected. This study compares the results of the 'train of four' test performed by neurophysiologists and anesthesiologists. Additionally, it looks at the differences, if any, in comparing stimulation of the foot nerve (tibial n.) or hand nerve (ulnar n.) Performing the TOF (train of four test) in the lower extremity can be relevant for many reasons. Train of four tests can show the presence of four twitches in the arms but the legs may not fully recovered from muscle relaxant given by anesthesia. Also, train of four test which uses subjective method of interpretation by anesthesiologists may present different results compared than objective quantitative method of train of four test interpretation. Ultimately, the goal of this study is to show the importance of 'TOF' testing in ensuring that any identifiable preventable intraoperative surgical complication is appropriately identified.

TOF test was performed by two routinely used devices, peripheral nerve stimulator and intraoperative neurophysiologic monitoring device. TOF monitoring of upper extremity included stimulation of ulnar nerve. Negative surface electrode was placed on the wrist in line with the smallest digit 1-2cm below skin crease and the positive 2-3cm proximal to the negative electrode. Active surface recording electrodes were placed on adductor pollicis muscle. TOF monitoring of lower extremity included stimulation of peripheral nerve, posterior tibial nerve. Surface stimulating electrodes were placed, negative over inferolateral aspect of medial malleolus, and positive electrode 2-3cm proximal to the negative electrode. Stimulation current was 20-30 mA for hand and 30-60mA foot TOF by a group of 0.2 millisecond pulses, spaced 500 millisecond apart, to deliver four contractions. Surface recording electrodes were used for measuring muscle response on foot, active electrode which was located on the Flexor hallucis brevis muscle and reference on the big toe. Intraoperative monitoring device was used, and software with TOF monitoring programe was installed. EMG response was calculated by the peak of amplitude (peak to peak amplitude) presented in quantitative value of online measurement. Interpretation was different, visual and subjective. Peripheral nerve stimulator was used for subjective TOF test. Output current was adjustable from 0 to 70 mA. Repeat stimulation of 4 pulses/0.2 milliseconds repeated every 500 milliseconds. Surface negative electrodes were placed over the course of ulnar nerve on the wrist, in line with the smallest digit, 1-2cm proximal from skin crease, and positive electrode 2-3 cm proximal. Response was followed on adductor pollicis muscle. All data were kept in electronic medical records and if data are not complete subjects were not included in the study. Results were compared between TOF methods on two different body sites, upper and lower extremity, by quantitative method and other comparison was made between subjective and quantitative method with TOF test located in both methods on the upper extremity.