Abstract: We included six RCTs (521 participants), comparing abdominal drainage and no drainage in patients undergoing emergency open appendectomy for complicated appendicitis. The studies were conducted in North America, Asia and Africa. The majority of the participants had perforated appendicitis with local or general peritonitis. All participants received antibiotic regimens after open appendectomy. None of the trials was at low risk of bias. There was insufficient evidence to determine the effects of abdominal drainage and no drainage on intra-peritoneal abscess at 14 days (RR 1.23, 95% CI 0.47 to 3.21; 5 RCTs; 453 participants; very low-quality evidence) or for wound infection at 14 days (RR 2.01, 95% CI 0.88 to 4.56; 5 RCTs; 478 participants; very low-quality evidence). The increased risk of 30-day overall complication rate (morbidity) in the drainage group was rated as very low-quality evidence (RR 6.67, 95% CI 2.13 to 20.87; 1 RCT; 90 participants). There were seven deaths in the drainage group (N = 183) compared to one in the no drainage group (N = 180), equating to an increase in the risk of 30-day mortality from 0.6% to 2.7% (Peto odds ratio (OR) 4.88, 95% CI 1.18 to 20.09; 4 RCTs; 363 participants; moderate-quality evidence). There is 'very low-quality' evidence that drainage increases hospital stay compared to the no drainage group by 2.17 days (95% CI 1.76 to 2.58; 3 RCTs; 298 participants).  Other outlined outcomes, hospital costs, pain, and quality of life, were not reported in any of the included studies. The quality of the current evidence is very low. The effect of abdominal drainage on the prevention of intra-peritoneal abscess or wound infection after open appendectomy is uncertain for patients with complicated appendicitis. The increased rates for overall complication rate and hospital stay for the drainage group compared to no drainage group is also subject to great uncertainty. Thus, there is no evidence for any clinical improvement by using abdominal drainage in patients undergoing open appendectomy for complicated appendicitis. The increased risk of mortality with drainage comes from eight deaths observed in just under 400 people recruited to the studies. Larger studies are needed to determine the effects of drainage on morbidity and mortality outcomes more reliably.

Plain-language summary: We searched for all relevant studies up to 30 June 2017. We identified six clinical studies involving a total of 521 participants. All six studies compared drain use versus no drain use in individuals having an emergency open appendectomy for complicated appendicitis. Studies were conducted in the USA, India, Kenya, Pakistan, and Turkey. The age of the individuals in the trials ranged from 0 years to 82 years. The analyses were unable to show a difference in the number of individuals with intra-peritoneal abscess or wound infection when comparing drain use with no drain use. The death rate was higher in the drainage group than in the no drainage group. The hospital stay was longer (about two days - an 43.5% increase on an 'average' stay) in the drain group than in the no drain group. None of the studies reported the costs, pain, and quality of life. Overall, there is no evidence for any clinical improvement by using abdominal drainage in individuals undergoing open appendectomy for complicated appendicitis. All of the included studies had shortcomings in terms of methodological quality or reporting of outcomes. Overall, the quality of the current evidence is judged to be very low.