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.