Reliability of submaximal stimulation for the train-of-four test using acceleromyography and electromyography with individualized stimulation currents

Purpose: The supramaximal stimulation (SMS) of the TOF test causes uncomfortable sensations in patients. We aimed to determine whether the submaximal stimulation would be reliable in TOF tests with reduced painful sensation. Methods: The accelomyography (AMG) and electromyography (EMG) monitor was applied at each arm and general anesthesia was induced and maintained by total intravenous anesthesia. At extubation, we conducted TOF test three times at each of four different currents: SMS, 70% SMS, 50% SMS, and 30% SMS. The same procedure was performed in the postanesthesia care unit (PACU) only with EMG, and the pain scores on the numerical rating scale (NRS) during the tests were recorded. Results: A total of 36 patients were enrolled. At extubation, TOF ratios with SMS in AMG and EMG were 112.0 +/- 13.1% and 93.7 +/- 8.9%, respectively. There were no significant differences in TOF ratios between the SMS and lower stimulation intensities. However, 30% and 50% SMS showed significantly higher rates of the unmeasurable results of tests in the PACU. In terms of the stimulation pain, NRS showed a downward pattern as the current decreased and was significantly lower at 50% and 30% SMS than the NRS at SMS. Conclusion: The TOF test with submaximal stimulation is still reliable and can reduce stimulation pain. Considering the importance of the TOF results in determining extubation, the authors suggest the minimal current for the TOF test as 70% SMS.