Bias between capnometry and venous carbon dioxide during initial assessment of pediatric emergency department...

The bias of capnometry (ETCO₂) and venous carbon dioxide (vpCO₂) among pediatric emergency department (PED) patients triaged to critical care areas is unknown. We aimed to explore correlations and bias between ETCO₂ and vpCO₂¸and identify predictors of bias.

This was an observational, video-based, retrospective study comparing ETCO₂ and vpCO₂. Pediatric patients with simultaneous ETCO₂ and vpCO₂ 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.

A total of 200 PED patients with ETCO₂ and vpCO₂ data were included. The median (interquartile range [IQR]) ETCO₂, vpCO₂, and ΔCO₂ in mmHg were 38 (32, 46), 49 (41, 61), and 11 (4, 20), respectively. ETCO₂ (r = 0.76) and ΔCO₂ (r = 0.71) were highly correlated with vpCO₂. The mean bias between ETCO₂ and vpCO₂ was -14.1 mmHg (95% confidence interval [CI], -41.9 -13.7). The bias between ETCO₂ and vpCO₂ increased at higher values of each measure. ETCO₂ sampling interface was the only independent predictor of vpCO₂ in our multivariate analysis. Patients requiring bag-valve mask (BVM) ventilation had the highest median bias between ETCO₂ and vpCO₂ (29 mmHg, IQR 15, 37).

ETCO₂ and vpCO₂ were highly correlated. However, bias increased at higher levels of both ETCO₂ and vpCO₂. Among PED patients, ETCO₂'s ability to approximate vpCO₂ diminishes with worsening hypercarbic respiratory failure.