Relationship between posttetanic count and response to carinal stimulation during vecuronium-induced neuromuscular blockade

The correlation between degree of peripheral neuromuscular blockade and response to carinal stimulation was evaluated in two groups of 25 patients: one group was anaesthetized with thiopental, N2O and halothane, and the other group received thiopental, N2O and fentanyl. The degree of peripheral blockade was evaluated using train-of-four (TOF) and posttetanic twitch (PTC) stimulation of the ulnar nerve. The degree of diaphragmatic paralysis was evaluated indirectly by stimulating the carina and observing the corresponding muscular response, which was graded as severe, mild or absent. During halothane anaesthesia a PTC of 0 always indicated that no response to carinal stimulation could be elicited. On the appearance of the first response to posttetanic twitch stimulation (PTC = 1), 2% of the patients showed a mild response to carinal stimulation. At the first response to TOF stimulation, 48% of the patients reacted with a mild response. During thiopental, N2O, fentanyl anaesthesia one of 25 patients showed a mild response to carinal stimulation at a PTC of 0. When PTC was 1, 20% of the patients reacted mildly to the stimulation. At the first response to TOF stimulation, 92% showed a response to carinal stimulation; 24% of these responses were severe, necessitating intervention. It is concluded that the TOF response elicited peripherally is a late sign of neuromuscular recovery of the diaphragm, and that the method of counting posttetanic twitches is superior to the TOF response in evaluating early recovery of this muscle. Further, to ensure total diaphragmatic paralysis, the neuromuscular blockade of the peripheral muscles should be so intense that no response to posttetanic twitch stimulation (PTC = 0) can be elicited.