Can mainstream end-tidal carbon dioxide measurement accurately predict the arterial carbon dioxide level of patients with acute dyspnea in ED

Objective: This study was designed to determine whether the mainstream end-tidal carbon dioxide (ETCO2) measurement can accurately predict the partial arterial carbon dioxide (Paco2) level of patients presented to emergency department (ED) with acute dyspnea.

Methods: This prospective, observational study was conducted at a university hospital ED, which serves more than 110 000 patients annually. Nonintubated adult patients presented with acute dyspnea who required arterial blood gas analysis were recruited in the study for a 6-month period between January and July 2010. Patients were asked to breathe through an airway adapter attached to the mainstream capnometer. Arterial blood gas samples were obtained simultaneously.

Results: We included 162 patients during the study period. The mean ETCO2 level was 39.47 ± 10.84 mm Hg (minimum, 19 mm Hg; maximum, 82 mm Hg), and mean Paco2 level was 38.95 ± 12.27 mm Hg (minimum, 16 mm Hg; maximum, 94 mm Hg). There was a positive, strong, statistically significant correlation between ETCO2 and Paco2 (r = 0.911, P < .001). The Bland-Altman plot shows the mean bias ± SD between ETCO2 and Paco2 as 0.5 ± 5 mm Hg (95% confidence interval, -1.3165-0.2680) and the limits of agreement as -10.5 and +9.5 mm Hg. Eighty percent (n = 129) of the ETCO2 measurements were between the range of ±5 mm Hg.

Conclusion: Mainstream ETCO2 measurement accurately predicts the arterial Paco2 of patients presented to ED with acute dyspnea. Further studies comparing mainstream and sidestream methods in these patients are required.