Twenty patients were prospectively included in this clinical trial, after permission at our institute. Patients having elective abdominal surgery with supra/infra-umbilical incisions were included. Patients opting for regional anesthesia or who were on long-term opioids were excluded. Informed written consent was obtained in the holding bay of the operating room suite. Randomisation of 20 patients was performed by alternating patients to either the TAP or control group.
General anesthesia (GA) was standardised in both groups using propofol 1-2 mg/kg (Propofol, Sandoz, Sydney NSW, Australia), rocuronium 0.5 mg/kg (Esmeron, Shering-Plough, Sydney, NSW, Australia), and fentanyl 100 μg (Fentanyl, Astra Zeneca, Sydney, NSW, Australia), used at preinduction and intubation and then up to 500 μg during maintenance. Maintenance of anesthesia was with 50:50 O2 and air with Sevoflurane. In the TAP group, the catheter was placed at the end of surgery, prior to extubation by the primary investigator under ultrasound guidance (Sonosite Inc Micromax, Bothell, WA, USA, PO 6468-10). In the control group, the mode of postoperative analgesia included regular Paracetamol (Perfalgan, Bristol-Myers Squibb, Victoria, Australia), 1 g 6 hourly and fentanyl patient controlled analgesia (PCA). In the TAP group, analgesia included continuous TAP block infusion, paracetamol 1 g 6 hourly and fentanyl PCA.
The technique used was posterior approach.[5
] The investigator was scrubbed and gowned and the ultrasound probe was covered by a sterile plastic cover and placed in the midaxillary line just superior to the iliac crest . After identifying the abdominal layers, the transversus abdominal plane was reached by using an 18-G Touhy's needle (Portex Epidural Minipack, Smiths Medical Australasia Pty, Brisbane, QLD, Australia). Correct placement of the needle tip was confirmed by injecting 5-10 ml of saline bilaterally. A bolus dose of 15 ml of 0.5% ropivacaine (Naropin, Astra Zeneca, Sydney, NSW, Australia) was administered . The epidural catheter (Portex Epidural Minipack, Smiths Medical Australasia Pty, Brisbane, QLD, Australia) was then advanced cephalad up to the 10-15 cm skin mark. The needle was removed and catheter connected to a bacterial filter. A 0.2% ropivacaine infusion at 8-10 ml/ hr was continued for 72 hours on each side. Our technique involved placement of the bevel of the needle superiorly, and then inserting the catheter and to advance it as superiorly as possible. The catheter needs to be advanced normally up to the 10 cm mark but may require to be advanced up to 15 cm mark in obese patients.
Tuohy needle (18-G) inserted anterior to Ultrasound transducer, which is held transversely in plane to perform the TAP block
Sonographic image of the abdominal muscles layers with local anesthetic spread in TAP. EO = External oblique, IO = internal oblique, LA = local anaesthetic in TAP, TA = transversus abdominis muscle
Pain scores were recorded on a numerical rating scale (NRS) from 0-10 both at rest and on coughing. The recovery staff in the post-anesthesia care unit (PACU) recorded pain score on arrival and at 1 hour postoperatively. Generally, patients are discharged from PACU with adequate pain relief after 1 hour. The Acute Pain Service team recorded the pain scores in the ward from day one to day three. Other observations recorded included the amount of fentanyl used at various pain assessment times, number of episodes of nausea and vomiting, and complications related to the procedure or catheter placement. Additionally, in order to assess satisfaction in the TAP analgesia group, patients were asked to rate their pain relief as poor, satisfactory, or excellent.
The sample size was adequate to detect a difference of three units in pain score between its group at anytime point with a significance level of P
= 0.05 and a power of 0.8. Pain scores are presented as median and interquartile range (IQR). Fentanyl use is presented as mean and standard error. Differences in pain scores were tested with a Mann–Whitney U
test and differences in fentanyl use with a t
test. All calculations were carried out using the R statistical language (R Foundation for Statistical Computing, Vienna, Austria; http://www.R-project.org