Pharmacodynamics of Rocuronium during Propofol and Isoflurane Anesthesia

Abstract

Background: This study was done to determine the pharmacodynamic characteristics of rocuronium during isoflurane and propofol anesthesia. Methods: Forty adult patients who underwent a tympanoplasty were randomly assigned to one of two groups which was given anesthesia maintained with isoflurane or propofol. Anesthesia was induced with propofol 2 mg/kg, and midazolam 0.2 mg/kg. The patients inhaled isoflurane through a mask or were infused with propofol. The electrodes were applied over the ulnar nerve at the wrist. Then, the patients were stimulated with a 50 Hz supramaximal tetanic stimulation for 5 seconds and a 1 Hz single twitch for 5 minutes to stablize muscle contraction and then a control value was obtained with accelerography (Organon technika bv, boseind 15, 5281 RM Boxtel, Netherland). Rocuronium 0.6 mg/kg (ED95 2) was injected. Thereafter, a 0.1 Hz single twitch of adductor pollicis was kept during the study. All patients were intubated after complete relaxation. We measured onset, clinical duration, and recovery index (RI). When patients showed a 75% recovery, a bolus of rocuronium (10-20 mg) was administered. Then, for 1 hour we determined the infusion rate of rocuronium necessary to produce a 90-95% neuromuscular block. Subsequently, we stopped the continuous infusion, and measured a second RI. After cessation of surgery, the infusion was stopped and the patients were allowed to recover spontaneously. We recorded a third RI. Results were expressed as mean SD. An unpaired t-test, and paired t-test (with Bonferroni's correction) were used to compare the variables between the two groups and RI's in each group. P 0.05 was considered significant. Results: Infusion rates were 269 ﾜ 70 and 321 65g/kg/hr in the isoflurane and the propofol groups, respectively (P 0.05). The onset time of isoflurane and propofol were 54.5 18.8 sec. and 80 F 35.1 sec., respectively (P 0.05). Conclusions: Isoflurane has a faster onset time and lower infusion rate of rocuronium than propofol. It seems to be due to a muscle relaxation effect of isoflurane.