Assessment of neuromuscular block: comparison of three clinical methods and evoked electromyography

Three clinical methods, visual, tactile and 'spring', for the assessment of neuromuscular blockade were compared to the EMG recording evoked during enflurane anaesthesia and relaxation with vecuronium in 33 patients. During maintenance of the block, the tactile method, based on the recognition of the strength of movement of the patient's thumb against the observer's fingers, was more accurate than the two other methods. The correlation coefficient compared to the TI of the EMG was 0.77. The tactile method led to over-estimation of muscle strength in only 9-10% of the assessments made by the anaesthetists, while this happened in about one-third of the cases when the visual method was applied. The observers under-estimated the muscle power in about 30% of the assessments made with each of the clinical methods. During the recovery, the mean train-of-four (TOF) ratio of the EMG was less than 40% when the anaesthetists announced that they could detect no fade with the visual or tactile methods. The corresponding value obtained with the spring method (standardized preload with a rubber spring) was significantly higher, 66%. Using the spring, a clinically significant residual fade (TOF less than 0.50) could be detected in nine of the 11 cases. As residual relaxation cannot be ruled out using the clinical methods, quantitative recording of neuromuscular function is recommended in cases where complete recovery from muscle relaxation is of special importance. The spring method is the most reliable clinical method during recovery, while the tactile method is the most accurate during the maintenance of neuromuscular block.