TIME TO PEAK EFFECT OF NEOSTIGMINE AT ANTAGONISM OF ATRACURIUM-INDUCED OR VECURONIUM-INDUCED NEUROMUSCULAR BLOCK

Study Objective: (1) To determine the time to peak. effect of neostigm ine (time to peak antagonism) during atracurium- or vecuronium-induced neuromuscular block; and (2) to determine the effect on time to peak effect of neostigmine during atracurium-induced neuromuscular block, w hen the dose of neostigmine is increased from 35 mu g/kg to 70 mu g/kg . Design: Prospective, randomized clinical study. Setting: Gynecologic operating room suite at a university hospital. Patients: 45 ASA I and II women admitted for gynecologic laparotomy. Interventions: Anesthes ia was performed with thiopental sodium, fentanyl, halothane, nitrous oxide, and atracurium of vecuronium. Train-of-four (TOF) stimulation a nd mechanomyography were used to monitor neuromuscular transmission. N eostigmine was administered while a constant degree of neuromuscular b lock was maintained at a twitch height at a point between 4% and 11% o f the control twitch height, wing a continuous infusion of atracurium or vecuronium. The patients were randomized to three groups, with 15 p atients in each group. Group 1 received atracurium block antagonized w ith neostigmine 35 mu g/kg; group 2 received vecuronium block antagoni zed with neostigmine 35 mu g/kg and group 3 received atracurium block antagonized with neostigmine 70 mu g/kg. Measurements and Main Results : The degree of neuromuscular block at antagonism was similar in the t hree groups. Time to peak effect (mean +/- SD) on TOF ratio war signif icantly longer in Group 1 (9.7 +/- 3.0 minutes) versus Group 2 (6.6 +/ - 1.4 minutes; (p < 0.05). The time to peak effect on TOF ratio during atracurium-induced block war reduced from 9.7 +/- 3.0 minutes to 6.3 +/- 2.0 minutes when the dose of neostigmine was increased from 3 mu g /kg to 70 mu g/kg (p < 0.05). The peak effect on TOF ratio war signifi cantly greater in Group 3 compared with Group 1 (p < 0.05, while it wa s similar in groups 1 and 2. Conclusion: The time to peak effect of ne ostigmine 35 mu g/kg is about 6 to 10 minutes when antagonizing a cons tant degree of atracurium- or vecuronium-induced neuro-muscular block at a twitch height at a point between 4% and 11%. Even though the time to peak effect was longer with atracurium than with vecuronium, clini cally significant differ ences between the antagonizing effect of atra curium versus vecuronium block were not demonstrated. The time to peak effect during atracurium-induced block decreased when the dose of neo stigmine was increased from 35 mu g/kg to 70 mu g/kg.