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 [Figure 1]. 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 [Figure 2]. 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.

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.

McDonnell et al. conducted the first study and reported that a single-shot TAP block was effective even in supra-umbilical incision surgery.[2] To support this in their initial study, they performed TAP block through the Petit's triangle using local anaesthetic and dye and demonstrated, using magnetic resonance imaging, definite spread of dye in the transverse plane from superior margin of iliac crest to the level of costal margin.[14] In addition, their study on volunteers achieved sensory block to T7 dermatome level. To support this, we placed a catheter at the same depth as the subcostal approach with the skin mark at 10 cm or more. This eliminates the need for a subcostal TAP block for supra-umbilical incisions. We achieved low pain scores and reduced fentanyl requirement in the TAP group.

Shibita reported TAP block use in gynecological procedures with sensory block up to T10 and recommended its use only in lower abdominal surgery.[15] Laffey reported that that the upper level of the TAP block prior to full spread could be misleading. Measurement of the full block height was achieved gradually over several hours after the performance of block.[16] Our study also showed its maximal benefit on day 1, with lower pain scores in the TAP block group.

The limitation to our study is that the level of block was not assessed in all cases. A randomised trial on a larger scale might confirm this. We are planning to conduct such a trial in the future.