Trial of a Transversus Abdominis Plane (TAP) Block in Laparoscopic Colorectal Surgery

A considerable component of post-operative pain following abdominal surgery arises from the anterior abdominal wall. Although laparoscopic surgery has been shown to reduce post-operative pain scores compared to open surgery, there is still the problem of abdominal pain arising, in particular, from the specimen extraction site. Commonly used regimes to counter this pain include intravenous opiate-based patient-controlled analgesia (PCA) pumps, although such drugs can have a detrimental effect on the post-operative recovery of bowel function and leads to an increased risk of post-operative nausea and vomiting (PONV). The consequence of these gastrointestinal complications is that the benefits to patients of laparoscopic surgery with enhanced recovery programmes are not fully realised.

The benefits of adequate postoperative analgesia include a reduction in the postoperative stress response, reduction in postoperative morbidity, and in colorectal surgery, improved surgical outcome. Other benefits of effective regional analgesic techniques include reduced pain intensity, decrease incidence of side effects from analgesics (such as PONV), and improved patient comfort.

The innervation of the anterior abdominal wall comes from nerve afferents from T6-L1 running in the neurovascular plane which is found between internal oblique and transversus abdominis (TA). The transversus abdominis plane (TAP) block aims to block these nerves with local anaesthetic before they pierce the anterior abdominal wall. It has already shown to be effective in reducing pain in the first 24 hours after a laparotomy when compared to PCA with opiates and shown to have potential in a series of patients undergoing radical prostatectomy.

The potential improvement of this technique is weighed against the added risks of injecting into the neurovascular plane. There is a theoretical risk of a significant flank haematoma as a result of injury to the small vessels running with the nerves. In addition there is the small risk of inadvertent peritoneal puncture although the risk of any subsequent significant injury is very small and would likely be detected at the time of subsequent laparoscopy. Although there is one case report of a needle puncture to the liver due to previously unknown hepatomegaly, the injury was detected at laparotomy and the consequences were insignificant.

Experimental Methods and Design Patients would be randomised to receive either 20mls of local anaesthetic on each side of the abdomen in the TA plane or to receive no additional treatment. Both groups would receive local anaesthetic into the wounds at the end of the procedure. The TAP block would take place after induction of anaesthesia but before commencement of surgery. The TAP block would be carried out in a standardised manner using ultrasound guidance by two experienced anaesthetists with considerable experience in this technique. For blinding purposes, the site of entry on the skin for a TAP block will be covered with a plaster, irrespective of whether a block has been given.

A standardised anaesthetic and a standard post-operative analgesia regimen will be given to both groups.

Patients will be withdrawn from analysis if a colorectal resection does not take place or the surgery is converted to an open procedure, although data will continue to be collected.