| Objective: Rocuronium bromide is an aminosteroidal neuromuscular blocking agent with rapid onset and intermediate duration of action. In clinical practice, it is commonly administered in combination with the volatile agents, especially isoflurane. Preliminary studies suggest that volatile agents potentiate the action of muscle relaxants. However, variability between subjects may confound these comparisons. Furthermore, to quantify the enhancement of the neuromuscular block produced by potent inhalation anaesthetics, it is important to start the investigation after adequate time has elapsed for isoflurane to diffuse into the muscular compartment. So a comparative randomized study was performed in the patients to investigate the dose-response relationship and the neuromuscular effect of rocuronium under the isoflurane anesthesia or the propofol anesthesia.Methods: Seventy-two ASA I or II patients were included, aged 18 to 60 years. A single-dose technique and the single-twitch mode of stimulation(acceleromyography, TOF-Watch SX) were used in the potency estimation part of the study. Without premedication, forty-eight patients were induced with midazolam 0.1mg/kg, fentanyl 4-5μg/kg and propofol 1.5-2mg/kg.Tracheal intubation was performed under 2% lidocaine local anaesthesia without the aid of neuromuscular blocking agents and anaesthesia was maintained according to a computer-generated randomization scheme with isoflurane (1MAC of end-tidal concentration, age adjusted) or propofol 3-6mg/kg/h. Standard hemodynamics, end-tidal CO2, and anesthetic gas concentrations were monitored continuously. After 40 minutes, a randomized dose (75, 150, 225 or 300 u g/kg) of rocuronium was administered via the venous line. Maximal depression of the twitch response was recorded to calculate the dose-response curve. It was determined by least squares linear regression of the logarithm of each dose against a probit transformation of the initial dose and response of each patient. The effective dose to obtain 50% and 95% neuromuscular block (ED50 and ED95, respectively) were calculated from individual dose-response curves. The action duration and recovery of rocuronium 0.6 mg/kg was determined in the other 24 subjects. Anaesthesia was induced with propofol TCI (target-controlled infusion), fentanyl 2 u g/kg and rocuronium 0.6mg/kg. Tracheal intubation was performed when maximal neuromuscular blocking achieved. Patients in the isoflurane group were maintained with 1MAC isoflurane of end-tidal concentration and 0.1-0.3 n g/kg/min remifentanil, while maintained with propofol TCI 2-3 u g/ml and 0.1-0.3 u g/kg/min remifentanil in the propofol group. The object was to ensure the BIS of 40-60, the heart rate and blood pressure in the range of ±30% of the basic line. The TOF mode of stimulation was used. The variables recorded were as follows: onset time (time from drug administration to maximum effects), no-response time (disappearance of Tl to appearance of Tl), times to recovery of Tl to 25% and 75% of control, recovery index (timefrom Tl 25% to 75%) and the TOF ratio to 0.25. The results of this part were analyzed using the Student's t test. .PO.05 was considered significant. Results: Mean ED50 and ED95 (95% confidence interval) of rocuronium were 152 (range, 131-175) and 314 (286-373) u g/kg in the propofol group, while they were 88 (72-104) and 263 (228-283) u g/kg in the isoflurane group. There were statistically significant differences in ED50 and ED95 between the two groups. In the dose of 0.6 mg/kg of rocuronium, 75% recovery time, TOF ratio 0.25 and recovery index were longer during isoflurane anesthesia than that of propofol anesthesia : (50.0 + 12.9) vs (37.7 + 10.8) min, (46.6 ± 12.5) vs (37.1 ±7.6) min and (17.8+5.3) vs (10.0+4.1) min, respectively (P < 0.05). There were no differences in onset time, no-response time and 25% recovery time between the two groups: (177.8 + 59.5 ) vs (177.8 + 59.4) sec, (18.3+4.5) vs (21.9 + 6.5) min, (27.7 + 7.5) vs (32.2± 10.6) min, respectively. Conclusions: In ASA I or II Chinese adult patients, ED50 and ED95 of rocuronium are significantly decreased under 1MAC isoflurane anesthesia compared with propofol anesthesia with single-dose method. Recovery time in a single dose of 0.6mg/kg of rocuronium is longer under 1MAC isoflurane and remifentanil anaesthesia than under stable propofol TCI and remifentanil anaesthesia. It shows that 1MAC isoflurane potentiates the potency and neuromuscular effect of rocuronium. |
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