Different recovery of the train-of-four ratio from rocuronium-induced neuromuscular blockade in the diaphragm and the tibialis anterior muscle in rat.

PURPOSE: To clarify differences between the diaphragm and the limb muscles in terms of the effects of neuromuscular blockers concerning train-of-four (TOF) ratios, we compared the recovery of twitch tensions and TOF ratios in the diaphragm and in the tibialis anterior muscle in rats in vivo.
METHODS: We conducted a dose-response study in 16 rats and a recovery study in 8 rats. In the recovery study, we made phrenic nerve-diaphragm and sciatic nerve-tibialis anterior preparations simultaneously in each of 8 rats that were anesthetized intraperitoneally with pentobarbitone (30 mg x kg(-1)) and urethane (500 mg x kg(-1)). After supramaximal stimuli were applied simultaneously in a TOF pattern to both the phrenic and sciatic nerves, rocuronium was injected intravenously, at 10 mg x kg(-1). In the diaphragm and the tibialis anterior muscle, we monitored the first-twitch response to TOF stimuli (T1) and also the TOF ratios. The following variables were determined for each muscle: (1) the times at which T1 recovered to 25%, 50%, and 75% of control T1, and the times at which the TOF ratio recovered to 25%, 50%, and 75%; and (2) the values of the TOF ratio at 25%, 50%, and 75% recovery of T1.
RESULTS: At 25%, 50%, and 75% recovery of T1 in the diaphragm, TOF ratios were 8.9 +/- 5.0 %, 26.7 +/- 7.7 %, and 55.9 +/- 5.4%, respectively, while in the tibialis anterior, the TOF ratios were 18.0 +/- 5.9%, 32.5 +/- 7.4%, and 54.4 +/- 7.5%, respectively (diaphragm vs tibialis anterior; P < 0.01 for comparisons at both 25% and 50% recovery of T1).
CONCLUSION: Our method of simultaneous in vivo evaluation of TOF ratios in both the diaphragm and the tibialis anterior confirmed significant differences between the two muscles in relationships between first-twitch tension and the TOF ratio.