ELSEVIER *Research Fellow tAssistant Professor XProfessor $4ssociate Professor Address correspondence to Dr. Brull at the Department of Anesthesiology, Yale Univer- sity School of Medicine, 333 Cedar St., P.O. Box 208051, New Haven, CT 065208051, USA. Received for publication January 24, 1996; revised manuscript accepted for publication May 29, 1996. Journal of Clinical Anesthesia 9:48-51, 1997 0 1997 by Elsevier Science Inc. Comparative Recovery of 50-Hz and loo-Hz Posttetanic Twitch Following Profound Neuromuscular Block Lori A. Fernandes, MD,* Robert G. Stout, MD,? David G. Silverman, MD,$ Sorin J. Brull, MD§ Department of Anesthesiology, Yale University School of Medicine, New Haven, CT. Study Objective: To determine if posttetanic twitch following 1 OO-Hz tetanic stimulation enables titration of a nondepolarizing relaxant infusion to a greater depth of block than that achieved with posttetanic twitch following 50 Hz. Study Design: Prospective, observational study. Setting: Operating rooms of a university tertiay care center. Patients: 10 ASA physical status II and IIIpatientsfi-ee of known neuromuscular disease and undergoing general endotracheal anesthesia for routine elective surgery. Interventions: Following induction of general anesthesia, neuromuscular block was maintained with a continuous intravenous vecuronium infusion. Depth of neuromuscular block was assessed by tactile evaluation of the evoked responses of the adductor pollicis muscle following supramaximal stimulation of the ulnar nerue via sur$ace electrodes. The wecuronium infusion was titrated to loss of posttetanic twitch following lOO-Hz tetanic stimulation, at which point the infusion was discontinued. Measurements and Main Results: lO@Hz tetanic stimulation was repeated every two minutes until recovery of thejrst posttetanic twitch, at which point 50~Hz tetanic stimu- lation was repeated every two minutes until recovery of the jrst posttetanic twitch. The median time (interquartile range) from discontinuation of the vecuronium infusion to recovery of the first posttetanic twitch following 1OQHz tetanic stimulation was 2 7 % faster than the corresponding time to recovery of the first posttetanic twitch following 5@Hz tetanic stimulation [I 9 (10 to 24) min and 24 (20 to 30) min respectively, p < 0.0021. Conclusions: Posttetanic twitch following 100Hz tetanic stimulation enables titration of a vecuronium infusion to a greater depth of block than posttetanic twitch following 50-Hz tetanic stimulation. The pesent jindings should enable more effective titration of this relaxant, thereby reducing the likelihood of unwanted patient movement or unduly pro- longed recovq due to relaxant overdosing. 0 1997 Elsevier Science Inc. Keywords: Measurement techniques: neuromuscular block, posttetanic twitch; nondepolarizing neuromuscular relaxants: vecuronium. Introduction For the past decade, counting the number of posttetanic twitches following a 50-Hz tetanic stimulation (PTC) has been used to assess profound degrees of 0952-8180/97/$17.00 655 Avenue of the Americas, New York, NY 10010 PI1 SO952-8180(96)00210-3