Influence of stimulation frequency on rocuronium and pancuronium-induced neuromuscular block onset: acceleromyography evaluation

Abstract

BACKGROUND AND OBJECTIVES: Factors associated to patients and neuromuscular blockers (NMB), as well as others inherent to neuromuscular function monitoring, may affect neuromuscular block onset. This study aimed at the influence of two different stimulation frequencies on rocuronium and pancuronium-induced neuromuscular block. METHODS: Participated in this study 120 patients, physical status ASA I and II, submitted to elective procedures under general anesthesia, who were randomly allocated in two groups, according to the stimulation frequency employed to monitor neuromuscular block: Group I - 0.1 Hz (n = 60) and Group II - 1 Hz (n = 60). Two subgroups were formed within each group (n = 30), according to the neuromuscular blocker: Subgroup P (pancuronium) and Subgroup R (rocuronium). Patients were premedicated with muscular midazolam (0.1 mg kg(-1)), 30 minutes before surgery. Anesthesia was induced with propofol (2.5 mg kg(-1)) preceded by alfentanil (50 microg kg(-1)) and followed by pancuronium or rocuronium. Patients were ventilated under mask with 100% oxygen until 75% or more decrease in adductor pollicis muscle response, when laryngoscopy and tracheal intubation were performed. Neuromuscular function was monitored by acceleration transducer. The following parameters were evaluated: pancuronium and rocuronium onset time; time for complete block and tracheal intubation conditions. RESULTS: Mean times (seconds) for pancuronium-induced neuromuscular block onset and for complete neuromuscular block were: Group I (159.33 +/- 35,22 and 222 +/- 46.56) and Group II (77.83 +/- 9.52 and 105.96 +/- 15.58); rocuronium-induced values were: Group I (83 +/- 17.25 and 125.33 +/- 20.12) and Group II (48.96 +/- 10.16 and 59.83 +/- 10.36) with statistical difference between groups. Tracheal intubation conditions were satisfactory in 117 patients (97.5%) and unsatisfactory in 3 (2.5%). CONCLUSIONS: Rocuronium and pancuronium-induced neuromuscular block onset and time required for complete adductor pollicis muscle neuromuscular block are shorter when higher stimulation frequencies are applied.