USE OF POST-TETANIC COUNT IN ASSESSMENT OF A REPETITIVE VECURONIUM-INDUCED NEUROMUSCULAR BLOCK

In order to evaluate the use of the post-tetanic count (PTC)method during repetitive administration of vecuronium, we studied20 patients allocated randomly to one of two groups: 10 patientsreceived droperidol-fentanyl anaesthesia (control group); 10other patients were given droperidol-fentanyl anaesthesia modifiedsubsequently by addition of 0.5% isoflurane (isoflurane group).Before tracheal intubation, a bolus dose of vecuronium 0.08mg kg^–1 was given i. v. followed by repeated doses of0.03 mg kg^–1. The twitch response of adductor polliciswas recorded after supramaximal stimulation of the ulnar nerveat the wrist using a Myograph 2000 neuromuscular transmissionanalyser. In the control group, a close correlation was foundbetween PTC and time to first reaction to train-of-four (TOF)nerve stimulation. This relationship was unchanged when comparingthe bolus dose and each of eight consecutive maintenance doses.Further, the degree and the duration of intense block were unchangedafter each of the eight maintenance doses. In the isofluranegroup, the relationship between PTC and time to first reactionto TOF stimulation remained unchanged after addition of isoflurane.However, isoflurane caused a significant prolongation of theduration of intense block and a corresponding lower PTC in allpatients. We conclude that PTC is a reliable method to evaluateintense neuromuscular block caused by vecuronium, even afterrepetitive administration of the drug and in combination with0.5% isoflurane. Presented in part at the annual meeting of the American Societyof Anesthesiologists, San Francisco, October 1988.