Analgesic effectiveness of transversus abdominis plane blocks after hysterectomy: a meta-analysis

Abstract

To determine the effectiveness of transversus abdominis plane blocks in gynecological surgery by systematic review and meta-analysis. Embase, MEDLINE and the Cochrane Library (CENTRAL) bibliographic databases were searched using a Cochrane Library search strategy modified for gynecological surgery. We included randomized controlled trials comparing transversus abdominis plane block with no block or placebo block. We retrieved 681 citations from which we included five published studies (225 randomized participants) which fulfilled our inclusion criteria, and identified a further six ongoing studies. Quality was assessed across six risk of bias domains: randomization sequence generation, allocation concealment, blinding, missing outcome data, selective reporting and other biases. Data were meta-analyzed where possible and presented as mean differences with 95% confidence intervals. Study quality was moderate. Compared with no block or saline placebo, transversus abdominis plane block provided significantly less postoperative pain at rest on a 10 cm visual analog scale at 2 h (mean difference −2.14 cm, 95% confidence interval (CI) –3.57 to −0.71) but not at 24 h postoperatively (–0.52 cm, 95% CI –1.49 to 0.45). Pain on movement showed similar results. Transversus abdominis plane block resulted in significantly less postoperative requirement for morphine use at 24 h (−11.76 mg, 95% CI −18.77 to −4.75) but not at 48 h (−16.01 mg, 95% CI −39.40 to 7.39). Evidence exists for the short-term efficacy (within 24 h) of transversus abdominis plane blocks during hysterectomy in terms of reported pain and morphine consumption, which may not be sustained at 48 h. Updates to this review should be undertaken periodically, and until further robust evidence is available, anesthetists should not rush to adopt this procedure into routine practice.

Introduction

Pain experienced after abdominal surgery, resulting from both the incision made to the abdominal wall and trauma to the internal viscera, can be considerable and is often inadequately controlled [1]. In addition to the negative emotional and physical suffering of the patient, postoperative complications can include respiratory difficulties, delays in mobilization and prolonged hospital stay [2], [3], [4]. For postoperative pain relief, non-opioid drugs, patient controlled intravenous strong opioids or central neuroaxial blockade are introduced in a stepwise fashion in response to reported pain intensity, usually combining two or more agents to provide adequate relief whilst minimizing adverse effects from any individual analgesic.

Peripheral nerve blockade is an alternative method of providing pain relief, which offers excellent selective analgesia across a wide range of surgical procedures whilst avoiding the side effects associated with central blockade, such as hypotension, urinary retention and epidural abscesses. Transversus abdominis plane block is a newer type of peripheral nerve blockade in which local anesthetic is injected into the neurovascular plane of the abdominal wall by the anesthetist, before the incision or just prior to wound closure. Nerves deriving from T6 to L1 pass through this plane before supplying the anterior abdominal wall [5], [6]. Two methods are employed to locate the transversus abdominis plane. In the “loss of resistance” approach, the triangle of Petit is located by palpation, with the blunt anesthetic needle placed by “double pop” penetration through the fascia of the external and internal oblique muscle [6]. Alternatively, needle placement can be guided by ultrasound [7].

A recent Cochrane review provided some limited evidence that transversus abdominis plane block reduces opioid consumption and postoperative pain, but that review included studies encompassing a range of abdominal surgical procedures and populations [8]. As a result of this case mix there may be other predictive factors of postoperative pain, for example the dermatome in relation to the incision, that could be masked by aggregation of studies in a single meta-analysis. Recent studies, however, have demonstrated that the spread of local anesthetic in transversus abdominis plane blocks given by the landmark approach is unlikely to provide the necessary sensory blockade over the area of incision associated with a cholecystectomy [9]. We therefore performed a systematic review of randomized trials of transversus abdominis plane blockade during elective gynecological surgery including hysterectomy.