The prognostic significance of the mechanism of mild to moderate alkalemia at emergency department admission

Paucity of evidence exists as to the prognostic significance of mild to moderate alkalemia upon presentation to the emergency department (ED). Patients presenting to the ED of one tertiary hospital over the last 24 years were included in this retrospective cohort study if the serum pH drawn within 3 h of the initial presentation was 7.45–7.55. Alkalemia was defined as primarily metabolic (PM) if PCO2≥35mmHg, and primarily respiratory (PR) if HCO3≤24mEq/L - otherwise, the etiology was considered to be mixed and the case was excluded from this analysis. The primary outcome was 30 days mortality, analysed by Cox’s regression. Of 25,884 patients included in the final analysis, 14,802 (47.4%) were PM and 11,082 (35.4%) PR. Adjusted for age, comorbidities, severity scores, potassium derangements, and year of admission, PR was associated with increased 30-day mortality (aHR 1.21, 95% CI [1.12–1.32]). The association of higher degree of alkalemia with increased mortality was significant only in the PM group (p < 0.001). The etiology of alkalemia (PR vs. PM) could provide important prognostication in the ED, even in mild to moderate cases. 1. In this large retrospective cohort we aimed to evaluate the prognostic implications of mild to moderate alkalemia (pH 7.45–7.55) upon presentation to the general ED. 2. Alkalemia that was primarily respiratory (PR) in etiology was associated with a decrease of 25% in the survival at 30 days compared to patients with primarily metabolic (PM) alkalemia, even when adjusted to patient age, comorbidities, and the severity of physiological derangement at presentation. 3. Higher pH was associated with increased mortality in the PM but not the PR group.