Effects of high vs. low perioperative inspired oxygen fraction on length of hospital stay and postoperative complications: a systematic review, meta-analysis, and trial sequential analysis

INTRODUCTION: Prolonged length of hospital stay (LOS) and postoperative complications in surgical patients are major public health issues worldwide. Perioperative hyperoxia may increase LOS, and the incidence of cardiac, cerebral, renal, and pulmonary injury; however, the supporting clinical evidence is controversial. Therefore, the current meta-analysis included all relevant randomized controlled trials (RCTs) to investigate the effect of high and low inspired oxygen fraction (FiO<inf>2</inf>) on LOS, according to postoperative complications. EVIDENCE ACQUISITION: Standard published RCTs were searched from bibliographic databases to identify all evidence reporting perioperative FiO<inf>2</inf> for patients undergoing surgeries. The primary outcome was LOS, and the secondary outcomes were postoperative organ complications, surgical site infection (SSI), and postoperative mortality. The relative risk (RR) and Peto-odds ratio (Peto-OR) for dichotomous outcomes and the mean difference (MD) and standardized mean difference (SMD) for continuous outcomes were estimated using a random-effects model. Trial sequential analysis (TSA) was performed in the meta-analysis to evaluate the required information sizes and assess whether the primary outcome in our meta-analysis was conclusive. EVIDENCE SYNTHESIS: Thirty-one RCTs with 10506 participants undergoing different surgeries were included. The LOS in the high FiO<inf>2</inf> group did not differ significantly from that in the low FiO<inf>2</inf> group (MD -0.01, 95% CI -0.10 to 0.08, P=0.81). Moreover, we found no meaningful evidence of subgroup differences in the primary outcome, in comparisons of FiO<inf>2</inf>, RCT type, surgery type, duration of oxygen inhalation or timing of oxygen inhalation. TSA results further suggested that the number of included studies was sufficient for the primary outcome. There was also no significant difference in postoperative organ complications (cardiac, cerebral, renal, and pulmonary), SSI (rate of SSI, ASEPSIS score, and ASEPSIS score > 20 cases), or postoperative mortality. For postoperative atelectasis, sensitivity analysis showed that after exclusion of one study, "Myles 2007," high FiO<inf>2</inf> was associated with increased postoperative atelectasis. CONCLUSIONS: The use of low FiO<inf>2</inf> has no effect on LOS, or the incidence of cardiac, cerebral, and renal injury or postoperative mortality. Compared with low FiO<inf>2</inf>, high FiO<inf>2</inf> did not reduce SSI which was contrary to the guidelines. Meanwhile, high FiO<inf>2</inf> may increase postoperative atelectasis in surgical patients.