Association between intraoperative end tidal carbon dioxide levels and postoperative nausea and vomiting: a systematic review and meta-analysis

The relationship between intraoperative end-tidal carbon dioxide (EtCO<inf>2</inf>) levels and postoperative nausea and vomiting (PONV) has gained research interest. This meta-analysis aims to elucidate the relationship between intraoperative EtCO<inf>2</inf> levels and PONV incidence through a systematic review and synthesis of available evidence, thereby addressing the existing knowledge gap in the perioperative care. We conducted a meta-analysis of randomized controlled trials (RCTs) to investigate this association, examining PONV incidence, nausea scores, and rescue antiemetic use. Our analysis included 10 RCTs (N.=1860), comparing EtCO<inf>2</inf> levels of <35 vs. ≥35 mmHg and <40 vs. ≥40 mmHg. In the random-effects statistical models, pooled risk/odds ratios (RR/ORs) or mean differences (MDs), 95%CIs, and P values were estimated for endpoints. In the first comparison (seven trials, N.=475), the RR for PONV incidence with higher EtCO<inf>2</inf> (≥35 mmHg) was 0.80 (95%CI, 0.35-1.84, P=0.60, I2=72%). In the second, (six trials, N.=1639), the RR for PONV with higher EtCO<inf>2</inf> (≥40 mmHg) was 0.82 (95% CI, 0.67-1.00, P=0.051, I2=0%). For other outcomes, nausea scores with high EtCO<inf>2</inf> (≥40 mmHg) showed a MD of 0.94 (95%CI: -1.55-3.43, P=0.46, N.=456). Rescue antiemetic use showed no significant reduction with hypercapnia (OR, 0.48, 95%CI: 0.21-1.06, P=0.07, N.=548). Meta-regression analysis revealed no significant associations between PONV incidence and predictors including age, BMI, laparoscopic surgery, female gender, surgery duration, and intraoperative EtCO<inf>2</inf> values (for EtCO<inf>2</inf>, meta-regression P=0.278). The analysis does not provide strong evidence that EtCO<inf>2</inf> levels are a key factor in influencing PONV incidence, even when the available covariates or the factors examined. Further large-scale, well-designed studies are needed to clarify this relationship and explore potential interactions with other PONV risk factors.