End-Tidal Carbon Dioxide as a Measure of Acidosis Among Children With Gastroenteritis

Abstract

OBJECTIVES. We aimed to determine the correlation between end-tidal carbon dioxide levels and serum bicarbonate concentrations among patients with gastroenteritis, to compare the end-tidal carbon dioxide with other clinical parameters that might also be associated with the degree of acidosis, and to examine the relationship between end-tidal carbon dioxide levels and return visits. METHODS. Our prospective sample included patients presenting to the emergency department with a chief complaint of vomiting and/or diarrhea. The association between end-tidal carbon dioxides and serum bicarbonate concentrations was determined with simple linear-regression analysis. Receiver operating characteristic curves were computed to determine the predictive ability of the end-tidal carbon dioxide to detect metabolic acidosis. RESULTS. One hundred thirty of 146 subjects who were approached were included in the final analysis. For those for whom laboratory studies were performed, the mean serum bicarbonate concentration was 17.3 ± 4.3 mmol/L and the mean end-tidal carbon dioxide level was 34.2 ± 5.2 mm Hg. End-tidal carbon dioxide levels and serum bicarbonate concentrations were correlated linearly in bivariate analysis. Receiver operating characteristic curves were calculated for end-tidal carbon dioxide as a predictor of serum bicarbonate concentrations of ≤13, ≤15, and ≤17 mmol/L, with areas under the curves of 0.94, 0.95, and 0.90, respectively. The relationship between end-tidal carbon dioxide levels and serum bicarbonate concentrations was independent of other potential predictors of acidosis in multivariable analysis. The mean end-tidal carbon dioxide level for patients who required an unanticipated return visit (33.0 ± 4.0 mm Hg) was lower than the level for those who did not seek reevaluation (36.6 ± 3.6 mm Hg). CONCLUSIONS. End-tidal carbon dioxide levels were correlated with serum bicarbonate concentrations among children with vomiting and diarrhea, independent of other clinical parameters. Capnography offers an objective noninvasive measure of the severity of acidosis among patients with gastroenteritis.