RESUMO
BACKGROUND: In surgical trials, complex variables such as equipment development and surgeons' learning curve are involved. The evidence obtained in these trials can thus fluctuate over time. We explored the stability of the evidence obtained during surgery by conducting a cumulative meta-analysis of randomized controlled trials for open and laparoscopic appendectomy. METHODS: We conducted a cumulative meta-analysis of randomized controlled trials comparing laparoscopic appendectomy with open appendectomy for acute appendicitis, a topic with the greatest number of trials in the gastroenterological surgical field. We searched the MEDLINE (PubMed), EMBASE, and CINAHL databases up to September 2014 and reviewed the bibliographies. Outcomes were the incidence of intra-abdominal abscess, incidence of wound infection, operative time, and length of hospital stay. We used the 95 % confidence interval (95 % CI) of effect size for the significance test. RESULTS: Sixty-four trials were included in this analysis. Of the 51 trials addressing intra-abdominal abscesses, our cumulative meta-analysis of trials published up to and including 2001 demonstrated statistical significance in favor of open appendectomy (cumulative odds ratio [OR] 2.35, 95 % CI 1.30-4.25). The effect size in favor of open procedures began to disappear after 2001, leading to an insignificant result with an overall cumulative OR of 1.32 (95 % CI 0.84-2.10) when laparoscopic appendectomy was compared with open appendectomy. CONCLUSIONS: The evidence regarding treatment effectiveness changed over time, after treatment effectiveness became significant in trials comparing laparoscopic and open appendectomy. Observing only the 95 % confidence interval of effect size from a meta-analysis may not provide conclusive results.