A randomized, double-blinded controlled clinical trial was carried out after obtaining approval from the regional ethics committee and written informed consent from the patients. We examined 44 American Society of Anesthesiology (ASA) physical status I and II patients, aged 20 to 70 years, scheduled to undergo an open appendectomy. Patients were excluded if there was a history of allergy to levobupivacaine, coagulopathy or infection at the needle insertion site. Patients who had a difficulty to cooperating were also excluded.
Patients were allocated into two groups with a randomized sequence table: one group to undergo US-TAP block with 0.5% levobupivacaine (TAP block group, n = 22) and the other group to receive standard care (control group, n = 22). The primary outcome was time to first analgesia after surgery. Assuming the median time to first analgesia for the control and TAP block groups is 15 and 35 minutes, respectively, a power analysis based on 80% power with a type I error of 0.05 determined that we needed 22 patients for each group. There was no significant difference between the two groups in age, weight, height, body mass index (BMI), sex, and ASA physical status ().
Demographic data and clinical characteristics
All patients received standard general anesthetic management. Noninvasive blood pressure, electrocardiography, pulse oximetry, and capnometry were applied. Anesthesia was induced with glycopyrrolate 0.2 mg, midazolam 0.05 mg/kg, thiopental sodium 4 mg/kg, and fentanyl 1-2 µg/kg followed by mask ventilation and intubation for 90 seconds after injection rocuronium 0.6 mg/kg. Anesthesia was maintained with nitrous oxide, oxygen and sevoflurane. Sevoflurane was maintained as 2 volume % during surgery; additionally, fentanyl 0.5-1 µg/kg was injected to control blood pressure and heart rate within 20% of baseline. End-tidal carbon dioxide (CO2) was maintained at 30-35 mmHg.
When vital signs were stable after intubation, experienced anesthesiologist who did TAP block more than 10 times performed the TAP block under ultrasound guidance with a Sonosite M-Turbo ultrasound device and a 5 to 12 MHz linear transducer (Sonosite, Bothell, WA, USA). After draping the needle insertion site, the probe was placed transversely on the level of the right anterior axillary line between the 12th rib and the iliac crest, and the external oblique, internal oblique and transversus abdominis muscles were identified (). A 22-gauge, 50-mm needle (Stimuplex, B. Braun, Melsungen, Germany) was inserted medial to the probe by the in-plane technique and advanced in a lateral direction. When the tip of the needle reached the TAP between the internal oblique and transversus abdominis muscles, 1 mL of 0.5% levobupivacaine and normal saline were injected into the patients of the TAP block group and control group, respectively, after negative aspiration, and the spread of the drugs was confirmed. Then, the remaining 19 mL was injected. Adequate diffusion of the drug was certified by an oval-shaped hypoechoic fluid pocket at TAP with real-time ultrasound imaging (). Besides checking negative aspiration and seeing needle did not puncture peritoneum or visceral organs on US view, the surgeon confirmed if peritoneum or visceral organs were intact for operation. At the end of the surgery, the total dose of intraoperative fentanyl was recorded. Pain intensity was assessed as the verbal numerical rating scale (VNRS: 0, no pain; 10, the severest pain imaginable) at arrival in the recovery room (time 0) and at 1, 3, 6, 12, 24 and 48 hours postoperatively. Every assessment of VNRS was performed by a blinded interviewer, and pain was scored under two conditions: at rest (VNRSr) and at coughing (VNRSc). Nausea/vomiting and dizziness events were also recorded. When the VNRSr was greater than 4 in the recovery room, ketorolac tromethamine (Ketorac, Daewoo Pharm Co., Busan, Korea) 30 mg as a rescue analgesic was given. After transfer to the ward, the patient was managed with a standard protocol including injection of ketorolac tromethamine 30 mg every 12 hours. When the VNRSr was higher than 4 or the patient wanted an analgesic, a rescue analgesic was given. When a patient refused a drug, even the basic protocol analgesic was not injected. All given analgesics at the recovery room and ward were recorded as doses and time given. And the time of first analgesia was recorded.
(A) Abdominal muscles and fascia before injection. (B) Abdominal muscles and fascia after 20 mL injection of local anesthetics to transversus abdominis plane.
Statistical analyses were performed using IBM SPSS ver. 18.0 (IBM Co., Armonk, NY, USA). Pain scores at each time period were compared using the Mann-Whitney U test. Total number of analgesics, intraoperative fentanyl use and the time to first analgesia were analyzed using Student t-test. Categorical variables were compared using chi-square analysis or Fisher exact test. In all tests, data with a P < 0.05 were considered statistically significant.