Subjects comprised 16 patients scheduled for orthognathic surgery, aged 17–36 years and classified in the American Society of Anesthesiologists (ASA) physical status I or II. After institutional approval, informed consent to participate in this study was obtained from each subject. All subjects were free from abnormal functions of kidney or liver and neuromuscular disease, and no drugs affecting neuromuscular transmission were used.
Prior to induction of general anesthesia, standard monitoring providing electrocardiography, noninvasive blood pressure, pulse rate, and SpO2 measurement was performed. An acceleration-sensing muscle relaxation monitor (S/5 Patient Monitor, Datex-Ohmeda, Helsinki, Finland) was set up. Stimulating electrodes of the muscle relaxation monitor were secured to the skin along the ulnar nerve in the right forearm, and mechanosensors were attached to the right thumb and index finger. Additional monitoring during general anesthesia included body temperature, end-tidal CO2, and invasive blood pressure measurement.
Anesthesia was induced with 100 µg fentanyl citrate (fentanyl, Fentanest, Daiichi Sankyo, Tokyo, Japan), intravenously, followed by a target-controlled infusion of propofol (Diprivan, AstraZeneca, Osaka, Japan) administered to achieve a predicted effect-site concentration of 4.0 µg/mL. After the subjects lost consciousness, 0.6 mg/kg rocuronium bromide was administered, and nasotracheal intubation was performed. Anesthesia was maintained by total intravenous anesthesia using room air, oxygen, and propofol. Supplemental analgesia during surgery was provided by repeated administration of fentanyl citrate or continuous infusion of remifentanil hydrochloride (Ultiva, Janssen Pharmaceutical, Tokyo, Japan) to maintain stable hemodynamic condition.
After nasotracheal intubation, an infusion of rocuronium bromide was started at 7 µg/kg/min, and the infusion rate was then adjusted to maintain a train of four (TOF) ratio at 10 to 15%. The TOF ratio just prior to oral mucosal injection of a 1% lidocaine hydrochloride solution containing 10 µg/mL epinephrine (1% Xylocaine, AstraZeneca) (LE) was taken as the baseline, and TOF ratio was observed for 20 minutes, with 1-minute intervals following the start of administration. The rate of rocuronium bromide continuous infusion was kept constant during the 20 minutes when TOF ratio was monitored. TOF changes were observed only in subjects for whom a local anesthetic solution was given 50 minutes or more after the start of continuous infusion of rocuronium bromide. Subjects were excluded from the study if drugs with circulatory action were used prior to or during observation of TOF.
Data are expressed as mean ± standard deviation. Repeated measures analysis of variance followed by Dunnett test was used for statistical analysis. P value less than .05 was considered statistically significant.