Research design
This was a prospective randomized controlled study conducted in the Department of Anesthesiology, the People’s Hospital of China Three Gorges University&the First People’s Hospital of Yichang, Hubei, China. The study protocol was approved by the institutional review board of the People’s Hospital of China Three Gorges University&the First People’s Hospital of Yichang, Hubei, China (20161103). The study was registered at www.chictr.org.cn with the identifier ChiCTR-IOR-16009753 on November 6, 2016. All participants provided written informed consent. Patients were recruited from December, 2016 to Januray, 2018.
Participants
Inclusion criteria consisted of women, ranging in age from 18 to 60 years, American Society of Anesthesiologists (ASA) physical status of I or II, gynecological laparoscopic surgery under general anesthesia, and less than 3 hours’ operation duration. Subjects didn’t suffered from hypertension, heart disease and diabetes. They had no medication history including regular beta-blocker, ACE-inhibitors, other cardiovascular medications and steroids. Included procedures were myomectomy, ovarian cystectomy and diagnostic procedures. Subjects have not received preoperative cytostatic, radiation or further pretreatment. Subjects were excluded if they had malignant tumors, hypertension, diabetes, heart disease, adrenal gland disease, severe renal or hepatic disease, a history of chronic pain, bradycardia, pregnant, a long history of systemic corticosteroid, analgesic and adrenergic receptor agonist and antagonist, or dependent on alcohol, nicotine or opioid. Subjects were also excluded if they were allergic to local anesthetic, the body mass index exceeded 35 kg/m2, converted to open surgery for laparoscopic failure, or TAP block failed. The fasting period for solids was 8 hours, and for clear liquids was 2 hours before surgery. All participants were in good nutritional status.
Study protocol
Following informed consent, subjects scheduled for gynecological laparoscopic surgery were randomized to the following groups: Control group (without TAP block); Ropivacaine group (only receiving 0.2% ropivacaine with total volume of 60 ml perineurally for TAP block); Low, Medium, High DEX + ropivacaine groups (receiving 0.2% ropivacaine combined with 0.25 µg/kg, 0.5 µg/kg, 1.0 µg/kg DEX with total volume of 60 ml perineurally for TAP block, respectively). The randomization was performed by the pharmacy department using a schedule provided by a statistics staff and was blinded to the anesthesia team, surgery team, patient and clinical investigators. The medicine was prepared by the pharmacist, labeled with study subject number, and physically delivered by pharmacy staff to the anesthesiologist performing the TAP block.
Subjects were taken to the operating room, and electrocardiography, heart rate (HR), pulse oxygen saturation and blood pressure were monitored. A 20 gauge peripheral intravenous catheter was inserted under local anesthesia, and infusion of Ringer’s lactate was started at the speed of 6-8 ml/kg/h. Midazolam (0.04 mg/kg) and sufentanil (0.1 µg/kg) were administered intravenously in patients. After sterile preparation and draping of the injection area, a four-quadrant ultrasound-guided (Mindray M9 13 mHz liner probe; Mindray Co. Ltd, Shenzhen, China) TAP block was performed using an in-plane technique by the same anesthesiologist using a 22 gauge plexus needle. The four-quadrant TAP block includes performing single-shot bilateral subcostal as well as posterior TAP blocks [16]. A total of 60 ml study solution containing ropivacaine and different concentration DEX was used for the four-quadrant TAP blocks with each site 15 ml. After block placement, sensory function was examined every 5 minutes during the next 20 minutes. Sensory function was assessed using a 3-point scale to pinprick with a toothpick (pinprick to abdominal wall: 0, normal sensation, sharp to pinprick; 1, pinprick felt but not sharp; 2, no sensation, pinprick not felt). The score of 2 indicates a successful TAP block.
After successful TAP block was confirmed, general anesthesia was induced with intravenous propofol (2-3 mg/kg), sufentanil (0.2-0.4 µg/kg), rocuronium (0.6 mg/kg), and lidocaine (1.5 mg/kg). After an endotracheal tube was placed, anesthesia was maintained with intravenous propofol at infusion rate of ranging from 4-6 mg/kg/h, remifentanil at infusion rate ranging from 0.1-0.4 µg/kg/min, and cisatracurium (0.05 mg/kg) intermittently for maintenance of neuromuscular blockade. Bispectral index was maintained between 40-60 during the operation. Once tube position was confirmed, positive pressure ventilation was started with tidal volume 6-8 ml/kg, and the respiratory rate was titrated to maintain the end-tidal CO2 between 35 and 45 mmHg. Intravenous flurbiprofen 1 mg/kg, sufentanil 0.1 µg/kg and tropisetron 4 mg were administered to the subjects at the end of surgery. The same surgeons performed all the procedures with the same laparoscopic surgical technique by using a pneumoperitoneum pressure of 12 mmHg (carbon-dioxide flow rate of 1.2 L/min). After operation, subjects received regular paracetamol 1 g every 6 h and intravenous dezocine (rescue analgesic) 0.1 mg/kg was administered when needed until the patient's rest pain score was 3 or less. In addition, subjects received regular ondansetron 4 mg every 8 h as an enhanced recovery protocol.
In order to minimize the effect of non-research factors on results, the same surgeon team served for all patients, the single anesthesiologist served for all TAP blocks and assessment of TAP block prior to induction of anesthesia. And there was a standardized protocol for anesthesia and intraoperative analgesics in this study.
Outcome measurements
A total of 5 ml whole vein blood sample was collected to detect the levels of serum cortisol (Cor), norepinephrine (NE), epinephrine (E), interleukin (IL) -6 and blood glucose (Glu) at predetermined time intervals including prior to induction (T0, baseline), prior to pneumoperitoneum (T1), prior to the end of pneumoperitoneum (T2), and at the end of surgery (T3), respectively. Blood samples were stored in capped vacutainer tubes at -80°C for determining stress hormones. Serum Cor, NE, E and IL-6 were measured by the corresponding enzyme linked immunosorbent assay kit from the Siemens Company. Consumption of propofol and remifentanil were recorded at the end of operation. The duration from the completion of anesthesia to awakeness of patient was also recorded. At the same timepoints, mean arterial pressure (MAP) and HR were recorded, respectively. Adverse events during the procedure were defined as follows: bradycardia: HR < 55 bpm; tachycardia: HR > 30% above baseline value; hypotension: systolic blood pressure (SBP) < 90 mmHg; hypertension: SBP > 140 mmHg. If any, were treated as follows: bradycardia: atropine 0.5 mg was administrated intraveniously; tachycardia: remifentanil 1 μg/kg was administrated intraveniously in titrated dose; hypotension: ephedrine 6 mg was administrated intraveniously in titrated dose; hypertension: propofol 20 mg was administrated intraveniously in titrated dose and increasing the infusion rate of propofol and remifentanil.
Patients were followed up at 1 (H1), 6 (H6), 12 (H12), and 24 (H24) hours after surgery. During the assessment, patients were asked to rate their pain at rest and with movement on a 0 to 10 numeric rating scale (0, no pain; 10, pain as bad as you can imagine), respectively. The total consumption of dezocines within 24 hours after surgery were recorded.
Sample size calculation
We anticipated a difference of 30% in the intraoperative stress marker levels between the control and treated groups as being clinically meaningful. A sample size of 22 subjects per group was estimated necessary to detect such a difference with a power of 80% at an alpha level of 0.05 based on the results of our pilot study, which was calculated using PASS software version 15.0 (NSCC, USA). We planned to include 25 patients each group to account for the potential dropouts.
Statistical analysis
Kolmogorov-Smirnov test was used to examine the normality of distribution of continuous outcomes. Normally distributed continuous variables, such as serum Cor, NE, E, IL-6, and Glu changes, MAP and HR over time, and postoperative pain scores at rest and with movement, were expressed as mean ± standard deviation (SD) and were compared using repeated-measures analysis of variance followed by a post hoc Tukey multiple-comparisons test where appropriate. Whereas comparisons to baseline were analyzed by a post hoc Dunnett multiple-comparisons test, and intergroup comparisons were analyzed by Tukey multiple-comparisons test, as indicated. The demographic characteristics, consumption of propofol, opioid, atropine and ephedrine during the operation and rescue analgesics after surgery, and anesthesia recovery time were compared using repeated-measure analysis of variance, whereas a post hoc Tukey multiple-comparisons test compared values between the 5 groups. Categorical data (including the ASA status and the incidence of bradycardia) were described as frequencies and proportions, and were analyzed by using Chi-square test. Data analysis was performed using IBM SPSS 19.0 (IBM Corp. Released 2010. IBM SPSS Statistics for Windows, Version 19.0. Armonk, NY: IBM Corp), and 2-tailed P < 0.05 was considered statistically significant.