Randomised controlled trials (RCTs) of transversus abdominis plane block versus placebo or no transversus abdominis plane in adults who underwent abdominal surgery were eligible for inclusion. The primary endpoint was morphine use in the first 24 hours after surgery. Secondary endpoints were morphine use in the first 48 hours, incidence of postoperative nausea and pain and visual analogue pain scores 24 hours after the operation. The method of placement included ultrasound guidance and open transversus abdominis plane block insertion. Comparisons with other analgesic modalities and measuring of anaesthetic agent concentrations were excluded. It appeared that trials with fentanyl as the patient controlled analgesia were excluded.
The included trials studied transversus abdominis plane mostly compared with placebo 0.9% saline solution; three studies used no placebo. Types of surgery included caesarean, colorectal, total abdominal hysterectomy, laparoscopic cholecystectomy, gynaecological cancer, large bowel resection and open appendectomy. Seven studies were ultrasound guided, one study was surgically placed and one study was no ultrasound used. Different local anaesthetics were used (for example ropivacaine). Some studies allowed use of diclofenac, ibuprofen and paracetamol.
The authors did not state how many reviewers undertook study selection.