Simple and cost effective clinical methods for measuring neuromuscular fade responses with emphasis on "train of four" fade.

Objective: To evaluate different pressure transducers, available in the operating room for pressure measurements, interfaced with common monitoring equipment, for quantitation of the train of four (TOF) fade during clinical neuromuscular block (NMB).

Method: We determined evoked pressure changes produced by the thumb in response to TOF stimuli. We studied the responses of: a) a membrane disc device, and b) modified pressure transducers which were placed directly under the distal phalanx of the thumb of the clenched hand. The responses were displayed/recorded on OR monitors. The optimal positioning of these thumb pressure sensing (TPS) devices and their sensitivity and accuracy during onset, spontaneous (partial) recovery and pharmacologic reversal of NMB, were determined in anesthetized patients during muscle relaxation (Vecuronium) and reversal (Neostigmine). Simultaneous comparisons were made on twenty eight patients between the TOF fade responses obtained by the TPS devices and by conventional electromyographic and/or mechanomyographic methods. Comparisons were made either between pairs of data (e.g. "t" test, correlation coefficients, measuring agreement) or between several "treatment" groups (ANOVA of repeated measures).

Results: Correlations between the results of the TPS devices and the other methods were the closest (r- > 0.8) at higher TOF (T4/T1) ratios (e.g. during reversal. Measuring agreement was satisfactory and no significant differences were detected between the regression data (e.g. slope, residuals, x-axis of the regression lines) of the T4/T1 ratios vs. time when comparing EMG and TPS data during reversal of NMB.

Conclusion: Measuring quantitatively the TOF fade by TPS devices is an economically feasible method for determining the adequacy of recovery from clinical non-depolarizing NMB.