Introduction:
Rocuronium and cisatracurium are representative neuromuscular blocking agents used widely because the former have features of fast onset of peak effect and short duration of muscle relaxation relatively while the latter have comparatively long duration relaxation time and break down by Hofmann elimination and ester hydrolysis. A combination of the two have a synergic effect may be also used with either the priming method for rapid sequence intubation. It would contribute both to determine the effective combination rate clinically and to predict the pharmacokinetic characteristics that determine how much the synergistic effect of this combination. The investigators studied whether the prediction is possible to have a sufficient effect of reducing the dose when combining the two muscle relaxants through monitoring muscle relaxation during surgery.
Materials and methods:
This study was conducted to 81 patients scheduled for elective mastoidectomy and tympanoplasty after obtaining written informed consent. All patients included the American Society of Anesthesiologists (ASA) physical status I-II, aged 20-60, BMI 20-30 kg/m2. The exclusion criteria were as follows: a history of allergy to the study drugs, neuromuscular disease, pregnancy or breast-feeding, preoperative medication of antipsychotics or neuroleptics known to interact with non-depolarizing neuromuscular blocking agents (NMBAs), serum creatinine level\>1.2 mg/dL, liver transaminase\>40 U/L. Anthropometric variables such as height, weight were measured in ward before surgery. BMI calculated as total body weight divided by the squared height. Ideal body weight (IBW) was calculated by the formula of Devine {50 kg + 2.3 × (height \[inch\]-60) for man and 45.5 kg + 2.3 × (height \[inch\]-60) for woman} and used to administrate NMBAs of initial dose. Lean body weight (LBW) was calculated by the formula of James {LBW (men) = (1.10 × Weight(kg)) - 128 × ( Weight2 / (100 × Height(m))2), (women) = (1.07 × Weight(kg)) - 148 × ( Weight2 / (100 × Height(m))2)}. Additive dose of NMBAs was administrated by LBW. Patients were randomly assigned to each group by opening of sealed allocation envelope. Each group were intubating dose group (Group I, n=27) combined ED95 rocuronium and ED95 cisatracurium, small amount reducing group (Group S, n=27) reduced 10% of each ED95 and large amount reducing group (Group L, n=27) reduced 20% of each ED95.
Monitoring and Medication:
In the operating room, monitoring was accomplished to patients with a noninvasive blood pressure, pulse oximetry, electrocardiography, thermometer, Bispectral Index (BIS VISTA Monitoring System; Aspect Medical Systems Inc, Norwood, MA, USA), and T1/T4 ratio used TOF-Watch® (Organon, Teknica B.V., Boxtel, the Netherlands). Every 5 min, measured things are recorded.
Premedications with midazolam 2 mg and glycopyrrolate 0.2 mg were administrated to patients intramuscularly 1 h before surgery. Before patients arrived in the operating room, rocuronium and cisatracurium were prepared by a nurse who was not involved in this study. The syringe containing each study drug was conveyed to the performer of this study as the status of shielding the scale. The syringes of rocuronium and cisatracurium used each other syringe. Anesthesia was induced with propofol 1.5-2.5 mg/kg, remifentanil 0.4-0.6 mcg/kg, afterward maintained with target controlled infusion (TCI) of propofol 5-10 mg/kg/hr and remifentanil 0.05-2 mcg/kg/min. The infusion pump (Orchestra Module DPS, Fresenius-Vial, Brezins, France) was operated with Minto's and Marshall's pharmacokinetic model for effect site TCI of remifentanil and propofol.
The opposite arm against operation side was used for neuromuscular monitoring and attached to armboard of TOF-Watch®. Each study drug was administrated to the patient and timer was started with T1/T4 ratio monitoring. The surface electrodes of ulnar nerve placed at the wrist and Train-of-four (TOF) stimulation was used as setting of supramaximal square wave impulses with 200μs duration, 2 Hz per 12sec. The investigators checked times to TOF ratio=0 (Onset), 1st TOF ratio\>25% (Duration 25%) and TOF 25-75% (Recovery Index), recovery time of 90% (TOF 25-90%) under total i.v. anesthesia (TIVA). Also the investigators checked the rate of additional rescue dose administrated with 10% of initial NMBAs dose, operation time from incision to surgical wound dressing, anesthesia time from entering to going out the operation room. Body temperature was maintained above 35°C using warm air blanket. The arterial pressure cuff was placed on the opposite arm against TOF monitoring.
Adverse Events and Management:
In all patients, anesthesia level was assessed based on a BIS score of 40-60. Moderate hypertension (\>120% of baseline) or hypotension (\<80% of baseline) was treated by increasing or decreasing rate of propofol infusion with fluid supplement. Severe hemodynamic change (systolic pressure \< 90 mmHg or \> 200 mmHg) was controlled by intravenous (IV) administration of phenylephrine 50 mcg or nicardipine 250 mcg repeatedly until being hemodynamic stable status. Unexpectedly, when hiccup or self-contained respiration was showed, additional rescue dose of NMBAs was administrated to the patient even though T1/T4 ratio was lower than 25%.
Statistical Analysis:
All data are expressed as means ± standard deviations (SDs), numbers (percentages), or medians (upper and lower quartiles), as appropriate. Data between the groups were compared using the χ2 test, Fisher exact test, independent t test, or the Mann-Whitney U test, as appropriate. To assess data normality, the Kolmogorov-Smirnov test was performed on the data set. According to a preliminary study, 24 patients would be required in each group with a power of 0.9 and a type I error of 0.05. Factoring in a drop-out rate of 10%, the investigators calculated that 27 patients would be required for each group. All statistical analyses were performed with the SPSS 18.0 (SPSS Inc., Chicago, IL, USA) program. A P value \<0.05 was considered statistically significant.
