Obese patients with acute dyspnea may be prone to misorientation from the emergency department (ED), due to impaired gas exchange evaluation and altered basal respiratory profiles. This study aims to evaluate the prognostic value of arterial blood pH in obese ED patients with acute dyspnea in comparison to non-obese counterparts.

Single-center observational study of a cohort of 400 consecutive ED patients with acute dyspnea. The primary endpoint was a composite of Intensive Care Unit admission (with critical care needs) or in ED mortality. Predictors of the primary endpoint were assessed using multivariable logistic regression and ROC curve analysis, in obese (BMI ≥ 30 kg·m⁻²) and non-obese patients.

252 patients who had arterial blood gas testing were analyzed including 76 (30%) obese comparable to non-obese in terms of clinical history. 51 patients were admitted to ICU and 2 deceased before admission (20 obese (26%) vs 33 non-obese (19%); p = 0.17). Factors associated with ICU admission were arterial blood pH (pH < 7.36 vs pH ≥ 7.36) and gender. In multivariate models adjusted for risk factors, pH remained the sole independent predictor in obese patients, with no predictive value in non-obese patients (ROC AUC: 0.74, 95% CI [0.60; 0.87], optimal threshold for pH: 7.36, odds ratio: 10.5 [95% CI 3.18; 34.68]).

Arterial blood pH may selectively predict critical care needs in ED obese patients with acute dyspnea, in comparison to non-obese. A falsely reassuring pH < 7.36 should be regarded as a marker of severity when assessing acute dyspnea in obese ED patients.