A close relationship between post-tetanic twitch and train-of-four responses during neuromuscular blockade by vecuronium.

The relationship between post-tetanic twitch (PTT) and train-of-four (TOF) responses after intravenous administration of vecuronium were studied using EMG in 20 patients under nitrous oxide and enflurane anesthesia. After the initial dose (0.2 mg.kg(-1)) of vecuronium, the detectable first twitch of PTT (PTT(1)) always preceded that of TOF (TOF(1)) with the mean time interval of 10.7 +/- 2.6 min. The post-tetanic count (PTC) which coincided with the first appearance of TOF(1) was 9.4 +/- 2.6. After the appearance of TOF(1), the magnitude of TOF(1) was almost identical to that of PTC(10) until full recovery from neuromuscular blockade was observed, whether the supplemental doses of vecuronium (0.03-0.04 mg.kg(-1) i.v.) were administered or not. The magnitude of TOF(2) was slightly lower than that of PTC(20). These results suggest that there is a close relationship between these two types of response, and by evaluating not only PTC but also the magnitude of each PTT, the recovery of TOF responses can be predicted and its extent be estimated fairly accurately.