METHODS: RCTs that compared probiotics or synbiotics to usual care or placebo and reported clinical and diarrheal outcomes were searched in 4 electronic databases from inception to March 8, 2022 without language restriction. Four reviewers independently extracted data and assessed the study qualities using the Critical Care Nutrition (CCN) Methodological Quality Scoring System. Random-effect meta-analysis and trial sequential analysis (TSA) were used to synthesize the results. The primary outcome was ventilator-associated pneumonia (VAP). The main subgroup analysis compared the effects of higher versus lower quality studies (based on median CCN score).

RESULTS: Seventy-five studies with 71 unique trials (n = 8551) were included. In the overall analysis, probiotics significantly reduced VAP incidence (risk ratio [RR] 0.70, 95% confidence interval [CI] 0.56-0.88; I2 = 65%; 16 studies). However, such benefits were demonstrated only in lower (RR 0.47, 95% CI 0.32, 0.69; I2 = 44%; 7 studies) but not higher quality studies (RR 0.89, 95% CI 0.73, 1.08; I2 = 43%; 9 studies), with significant test for subgroup differences (p = 0.004). Additionally, TSA showed that the VAP benefits of probiotics in the overall and subgroup analyses were type-1 errors. In higher quality trials, TSA found that future trials are unlikely to demonstrate any benefits of probiotics on infectious complications and diarrhea. Probiotics had higher adverse events than control (pooled risk difference: 0.01, 95% CI 0.01, 0.02; I2 = 0%; 22 studies).

CONCLUSION: High-quality RCTs did not support a beneficial effect of probiotics on clinical or diarrheal outcomes in critically ill patients. Given the lack of benefits and the increased incidence of adverse events, probiotics should not be routinely administered to critically ill patients.