Following ethics committee approval (Ethics Committee No:5 Ankara/Turkey), 60 patients classified as American Society of Anaesthesiolgists (ASA) I-IIwho were 18–65 years old and who underwent elective arthroscopic shoulder surgery by the same surgeon were included in this prospective, randomized, double-blind clinical trial. At the preoperative visit, details of the anaesthetic technique and study protocol were fully explained, and written consent was obtained from each patient prior to the study. Those who had general contraindications for ISB, obstructive pulmonary disease, diabetes, neuropathy, contralateral diaphragmatic paralysis, a history of allergic reaction to any of the study drugs, ongoing hypnotic therapy, or any documented preoperative systemic disease that could interfere with general anaesthesia were excluded from the study. None of the patients received premedication. In the operating room, an intravenous (IV) catheter was inserted on the non-operated side, and standard monitors were applied (GE Datex-Ohmeda S/5™ Anaesthesia Monitor, Helsinki, Finland). The baseline bispectral index score (BIS), heart rate (HR), noninvasive blood pressure, peripheral oxygen saturation (SpO2), and respiratory rate (RR) values were recorded and measured at predetermined time intervals throughout the surgery. From a list of random numbers, instructions for randomization were prepared in sealed envelopes for each patient before the start of the study. The patients were allocated into one of three groups in a double-blind manner. Group B (
n = 20) received a single-shot ISB with bupivacaine 0.25 % (Marcaine, Astra Zeneca, Sweden) 40 ml before induction. Group L (
n = 20) received a single-shot ISB with levobupivacaine 0.25 % (Chirocaine, Abbott Laboratories, North Chicago, USA) 40 ml before induction in combination with GA. Group C (
n = 20) received GA alone. The nurse preparing and labeling the study drugs was blinded to the study procedures. In addition, the blocks and measurements throughout the study were performed by two different anesthetists who were also blinded to the treatment groups. The skin was cleaned with an antiseptic solution and 1 ml of lidocaine, of which 20 mg/ml was used for infiltration of the skin of the injection site subcutaneously. A standardized ISB technique was employed by following Winnie’s landmarks using a nerve stimulator and a 22-gauge x 50 mm stimulating needle (Stimuplex®; B. Braun, Melsungen AG, Germany) [
8]. The initial current output of the nerve stimulator was set at 1 mA at 2 Hz. The interscalene groove was identified with the patient’s head turned to the side opposite to that being blocked. Skin puncture was performed, and the needle was advanced until a contraction of the deltoid or biceps muscle appeared [
9]. The needle position was then adjusted until a twitch could still be elicited at a current output of less than 0.3 mA. After a negative aspiration test, the local anaesthetic was injected. Immediately after block placement, sensory block was assessed by pinprick at one minute intervals in the C4-6 dermatomes by a clinician unaware of the injected solution. After evidence of a successful sensory and motor block was obtained, the patients received a standardized anaesthetic protocol. Following administration of 100 % oxygen, anaesthesia was induced with IV thiopental 5–7 mg/ml and IV fentanyl 2 μg/kg. Then the patients received IV rocuronium 0.6 mg/kg, and the trachea was intubated so that the lungs were mechanically ventilated with a tidal volume of 8–10 ml/kg, with the ventilatory rate adjusted to maintain an end-tidal carbon dioxide concentration (partial pressure) of 30–35 mm Hg. Anaesthesia was continued with delivered (FD) desflurane 6 % (FD desflurane Suprane®, Baxter, Puerto Rico, USA) in 60 % nitrous oxide with oxygen, and the fresh gas flow was standardized. The desflurane concentration was then titrated to keep the BIS score in the 40–60 range. If the BIS value was less than 40 for more than 30 seconds, the FD desflurane was decreased by 25 %. If the BIS values exceeded 60 formore than 30 seconds, an ‘inhalation bolus of desflurane’ was administered [
10]. The patients did not receive any additional fentanyl doses. Hypotension (a 20 % decrease in relation to the baseline value) and bradycardia (HR < 45 beats/min) were recorded. The hypotension was treated with IV fluid replacement or by a decrease in the desflurane concentration keeping the limits of BIS score in the 40–60 range. If these limits couldn’t be achieved by changes in desflurane concentrations, then it was’t altered any more and, IV ephedrine 3–6 mg was used if necessary. In cases of bradycardia, IV atropine 0.5-1 mg was administered. Intraoperative muscle relaxation was provided by administration of incremental doses of 0.2 – 0.3 mg/kg of rocuronium. Fifteen minutes before the expected end of surgery, the desflurane was reduced in all patients to facilitate rapid emergence from the anaesthesia. At the beginning of skin closure, both nitrous oxide and desflurane administration were interrupted. The fresh gas flow was increased to 6 l/min of pure oxygen at the end of skin closure, and the recovery period began. Tracheal extubation was not carried out until the patient had adequate spontaneous ventilation with a tidal volume > 4 ml/kg and responded to verbal commands. Residual neuromuscular blockade was reversed with atropine 15 μg/kg IV and neostigmine 40 μg/kg IV if necessary. Emergence from anaesthesia was assessed by measuring the time to spontaneous eye opening and tracheal extubation, the latter corresponding to the end of the recovery period. Anaesthetic gas consumption was measured each time by the same observer who was blinded to the groups to which the patients were assigned.
The desflurane was administered by a Sigma Alpha vaporizer (Penlon Limited, UK), and the amount used was measured in milliliters after completion of each surgical procedure by refilling the vaporizer, which initially had been completely full. After surgery, all patients were transferred to the postanaesthesia care unit (PACU), where the heart rate (HR), mean arterial pressure (MAP) and respiratory rate (RR) were monitored. Side effects, such as hypotension, nausea, vomiting, hoarseness, Horner’s syndrome, and dyspnea, were documented. Patient satisfaction (0 = not satisfied, 1 = moderate, 2 = good, 3 = very good) and postoperative pain scores [using a 10 cm Visual Analog Scale (VAS) in which 0 cm = no pain and 10 cm = the worst pain imaginable] were evaluated on arrival at the PACU and at two, four, six, eight, and 24 hours after surgery. The duration of analgesia (time to first requested analgesic) was recorded, and the supplemental postoperative analgesia was standardized. If the VAS was ≥ 3, patients received 75 mg of intramuscular (IM) diclofenac followed by 50–100 mg of IV tramadol if the VAS remained unchanged after 30 minutes. Patients were discharged from the PACU according to the Aldrete discharge criteria [
11].
Statistical analysis
The primary end point of this study was defined as a reduction in desflurane consumption. Sample size estimation was performed by using MINITAB 15 software. Sample size was predetermined by using a power analysis: α = 0.05 and β = 0.2, and this showed that 19 patients per group would be sufficient. Data analysis was performed using the SPSS version 11.5 software program (SPSS Inc., Chicago, Illinois, USA). The Kolmogorov-Smirnov test was used to test the normality of distribution for continuous variables. The data was expressed as the number of patients and mean ± standard deviation (SD) (minimum-maximum), where applicable. For parametrical data, one way analysis of variance (ANOVA) was used, and the Bonferroni correction was applied when there was a significant difference. The repeated hemodynamic parameters and VAS were analyzed by repeated measures ANOVAwith Bonferroni adjustment for multiple comparisons. For gender, analgesic need, patient satisfaction, side effects, and ASA, the chi-square or Fisher’s exact tests were used. Statistical significance was set at a p value <0.05 for all analyses and p < 0.033 (0.1/3) for those that underwent Bonferroni adjustment.