Bias between capnometry and venous carbon dioxide during initial assessment of pediatric emergency department patients: A video-based study.

Objective: The bias of capnometry (ETCO) and venous carbon dioxide (vpCO) among pediatric emergency department (PED) patients triaged to critical care areas is unknown. We aimed to explore correlations and bias between ETCO and vpCO¸and identify predictors of bias.

Methods: This was an observational, video-based, retrospective study comparing ETCO and vpCO. Pediatric patients with simultaneous ETCO and vpCO data were included. Our primary aim utilized linear regressions to determine correlations and Bland-Altman analysis to assess bias. Our secondary aim utilized multiple regression to identify clinical covariates contributing to bias. Covariates included age, respiratory rate, heart rate, mean arterial blood pressure, capnometry interface, PED diagnosis, and PED disposition.

Results: A total of 200 PED patients with ETCO and vpCO data were included. The median (interquartile range [IQR]) ETCO, vpCO, and ΔCO in mmHg were 38 (32, 46), 49 (41, 61), and 11 (4, 20), respectively. ETCO ( = 0.76) and ΔCO ( = 0.71) were highly correlated with vpCO. The mean bias between ETCO and vpCO was -14.1 mmHg (95% confidence interval [CI], -41.9 -13.7). The bias between ETCO and vpCO increased at higher values of each measure. ETCO sampling interface was the only independent predictor of vpCO in our multivariate analysis. Patients requiring bag-valve mask (BVM) ventilation had the highest median bias between ETCO and vpCO (29 mmHg, IQR 15, 37).

Conclusion: ETCO and vpCO were highly correlated. However, bias increased at higher levels of both ETCO and vpCO. Among PED patients, ETCO's ability to approximate vpCO diminishes with worsening hypercarbic respiratory failure.