Neuromuscular sensitivity to tubocurarine. A comparison of 10 parameters

The pharmacometrics of neuromuscular block by tubocurarine was studied. Ten parameters were compared for the sensitivity, the scatter and the linearity of response at three levels of block in 11 cats. The fourth twitch of the train-of-four is the most sensitive parameter, followed in order of decreasing sensitivity by the train-of-four fade, the faded tetanus, the tetanus, the single twitch, the post-tetanic twitch and the tetanic fade. At the level of 50% block of the single twitch, all other parameters differ significantly (P less than 0.05) from the single twitch in sensitivity. With the exception of the tetanic fade, all parameters examined correlate with the single twitch (r xy = 0.42-0.77). This permits limited translation of results among various parameters. In cats the scatter of results is least for the most sensitive parameter, and vice versa. We conclude that the train-of-four is the most sensitive parameter, and that the single twitch is valid for an over-all estimation of the neuromuscular block induced by tubocurarine.