Stabilization and stability of twitch force during mechanomyography of theadductor pollicis muscle

Objective. In order to study the stabilization time, the increase in twitch force during stabilization and the maintenance of stability during mechano myography of the adductor pollicis muscle, neuromuscular function was monit ored in 20 patients anaesthetized without the use of a neuromuscular blocki ng agent. The effect of the type of stimulation (single twitch [ST; 0.1 Hz] , or train-of-four [TOF; 4 stimuli at 2 Hz, repeated every 12 s]) on these variables was studied. When applying TOF stimulation, the variables were al so investigated for the TOF percentage [quotient of fourth and first twitch of a TOF stimulus x 100%]. Methods. Two groups of ten patients were monito red with either ST or TOF stimulation. Measurements continued for at least 45 minutes. Multiple linear regression analysis was applied to examine the effect of stimulation on the stabilization time and the increase in twitch force. Results. According to our criteria for stability, we found that thr stabilization time did not differ for ST (13.7 [10.2] min; mean [sd]) and T OF stimulation (18.1 [9.6] min) (p > 0.10). Stabilized twitch forces were l arger during TOF than during ST stimulation (134% [19] and 113% [11]; p = 0 .01). In both groups of stimulation, sis patients showed an interruption of stability. The TOF percentage was stable throughout rile measurement perio d in all patients. Conclusions. Stabilization of twitch force takes too lon g for many studies of neuromuscular function in the clinical research setti ng. Therefore, we do not recommend its routine use when performing mechanom yography of the adductor pollicis muscle.