Relationship between post-tetanic twitch and single twitch response after administration of vecuronium.

We have studied the relationship between post-tetanic twitch (PTT) and single twitch response after administration of vecuronium 0.2 mg kg-1 in 100 patients during neuroleptanaesthesia (NLA) (droperidol and fentanyl) and during anaesthesia with halothane, isoflurane, enflurane or sevoflurane (1 MAC in nitrous oxide and oxygen). Intervals from PTT1 to single twitch, and post-tetanic-count (PTC) (number of PTT responses) at the onset of single twitch were determined electromyographically. These intervals in the isoflurane, enflurane and sevoflurane groups differed from those in NLA and halothane groups. PTC in the isoflurane, enflurane and sevoflurane groups differed from those in the NLA group, and PTC in the sevoflurane group significantly from those in the NLA and halothane groups. These results are consistent with the view that PTT reflects prejunctional block, whilst the single twitch response is indicative of postjunctional block.