Abstract: This review included six randomised controlled trials that enrolled a total of 564 adults undergoing elective midline laparotomy for colorectal resection comparing continuous wound infusion of a local anaesthetic to a normal saline placebo. Due to 23 post-randomisation exclusions, a total of 541 participants contributed data to the analysis of at least one outcome (local anaesthetic 268; control 273). Most participants were aged 55 to 65 years, with normal body mass index and low to moderate anaesthetic risk (American Society of Anesthesiologists class I-III). Random sequence generation, allocation concealment, and blinding were appropriately carried out in most trials. However, we had to downgrade the certainty of the evidence for most outcomes due to serious study limitations (risk of bias), inconsistency, indirectness, imprecision and reporting bias. Primary outcomes On postoperative day 1, pain at rest (mean difference (MD) −0.59 (from 3.1), 95% confidence interval (CI) −1.12 to −0.07; 5 studies, 511 participants; high-certainty evidence), pain on movement (MD −1.1 (from 6.1), 95% CI −2.3 to −0.01; 3 studies, 407 participants; low-certainty evidence) and opioid consumption via PCA (MD −12 mg (from 41 mg), 95% CI −20 to −4; 6 studies, 528 participants; moderate-certainty evidence) were reduced in the local anaesthetic group compared to the control group. Secondary outcomes There was a reduction in the time to first bowel movement (MD −0.67 from 4.4 days, 95% CI −1.17 to −0.17; 4 studies, 197 participants; moderate-certainty evidence) and the length of hospital stay (MD −1.2 from 7.4 days, 95% CI −2.0 to −0.3; 4 studies, 456 participants; high-certainty evidence) in the local anaesthetic group compared to the control group. There was no evidence of a difference in any serious postoperative adverse events until hospital discharge (RR 1.04, 95% CI 0.68 to 1.58; 6 studies, 541 participants; low-certainty evidence) between the two study groups. After elective midline laparotomy for colorectal resection, continuous wound infusion of a local anaesthetic compared to a normal saline placebo reduces postoperative pain at rest and the length of hospital stay, on the basis of high-certainty evidence. This means we are very confident that the effect estimates for these outcomes lie close to the true effects. There is moderate-certainty evidence to indicate that the intervention probably reduces opioid consumption via PCA and the time to first bowel movement. This means we are moderately confident that effect estimates for these outcomes are likely to be close to the true effects, but there is a possibility that they are substantially different. The intervention may reduce postoperative pain on movement, however, this conclusion is based on low-certainty evidence. This means our confidence in the effect estimate is limited. The true effect may be substantially different from the estimate of the effect. There is low-certainty evidence to indicate that the intervention may have little or no effect on the rates of any serious postoperative adverse events until hospital discharge. High-quality randomised controlled trials to evaluate the intervention with a focus on important clinical and patient-centred outcomes are needed.

Plain-language summary: We searched for clinical trials to January 2019 looking at the benefits and harms of continuous injection of a local anaesthetic after surgery to remove the bowel through a vertical cut in the abdomen. We looked for trials comparing local anaesthetic to an inactive substance (placebo) such as salty water (normal saline). We found six clinical trials including 541 participants. Most participants were aged 55 to 65 years, of varying health status from fit and healthy to having a severe systemic disease (a disease that affects the whole body). In people who received a local anaesthetic, pain at rest, pain on movement, and requirement for morphine-like pain killers were reduced on the first day after surgery compared to people who received an inactive substance. People who received a local anaesthetic also opened their bowels about half a day earlier and were discharged from hospital about a day earlier compared to people who received an inactive substance. We did not find a difference between people who received a local anaesthetic and those who received an inactive substance in the rates of any serious complications after surgery until hospital discharge. We rated the certainty of the evidence from studies using four levels: high, moderate, low, very low. Reasons for downgrading the certainty of the evidence included limitations problems with the design of the studies, missing data, differences between trials and how the outcomes were measured, and the small number of participants. We need more high-quality trials to evaluate this treatment, especially its effects on recovery after surgery, side effects and complications. We rated the certainty of the evidence for pain after surgery at rest and the length of hospital stay as high, meaning that we are very confident in the findings about the effects of the treatment on these outcomes. We rated the certainty of the evidence for the requirement for morphine-like pain killers and the time until the first bowel movement as moderate. This means that we are moderately confident in the findings about the effects of the treatment on these outcomes. We rated the certainty of the evidence for pain after surgery on movement and the rates of any serious complications after surgery until hospital discharge as low, meaning that we have limited confidence in the findings about the effects of the treatment on these outcomes.