Acidemia does not affect outcomes of patients with acute cardiogenic pulmonary edema treated with continuous positive airway pressure

Abstract

Introduction: A lack of data exists in the literature evaluating acidemia on admission as a favorable or negative prognostic factor in patients with acute cardiogenic pulmonary edema (ACPE) treated with non-invasive continuous positive airway pressure (CPAP). The objective of the present study was to investigate the impact of acidemia on admission on outcomes of ACPE patients treated with CPAP.

Methods: This was a retrospective, observational study of consecutive patients admitted with a diagnosis of ACPE to the Emergency Department of IRCCS Fondazione Cà Granda Ospedale Maggiore Policlinico, Milan, Italy, between January 2003 and December 2006, treated with CPAP on admission. Two groups of patients were identified: subjects with acidemia (acidotic group), and those with a normal pH on admission (controls). The primary endpoint was clinical failure, defined as switch to bi-level ventilation, switch to endotracheal intubation or inhospital mortality.

Results: Among the 378 patients enrolled, 290 (77%) were acidotic on admission. A total of 28 patients (9.7%) in the acidotic group and eight patients (9.1%) among controls experienced a clinical failure (odds ratio = 1.069, 95% confidence interval = 0.469 to 2.438, P = 0.875). Survival analysis indicates that, among acidotic patients, the time at which 50% of patients reached the 7.35 threshold was 173 minutes (95% confidence interval = 153 to 193). Neither acidemia (P = 0.205) nor the type of acidosis on admission (respiratory acidosis, P = 0.126; metabolic acidosis, P = 0.292; mixed acidosis, P = 0.397) affected clinical failure after adjustment for clinical and laboratory factors in a multivariable logistic regression model.

Conclusions: Neither acidemia nor the type of acidosis on admission should be considered risk factors for adverse outcomes in ACPE patients treated with CPAP.

Figure 1

Clinical failure rate of the study population by pH value on admission. The 95% confidence intervals of the control group are depicted with dashed horizontal lines.

Figure 2

Time course of pH during continuous positive airways pressure treatment. The time course of mean arterial blood pH during continuous positive airways pressure treatment in the acidotic group and in controls. Adjusted for age and sex; missing data replaced with the last observation carried forward technique.

Figure 3

Survival analysis of time to pH ≥7.350 among acidotic patients. Dotted lines indicate the time at which 50% of the sample reached the threshold pH (173 minutes).

Figure 4

Time course of pH and PaCO₂ during continuous positive airways pressure treatment. Time course of pH and partial pressure of carbon dioxide in arterial blood (PaCO₂) during continuous positive airways pressure treatment in the controls and in the acidotic group according to the diagnosis (after replacing the missing values according to the last observation carried forward technique and after adjustment for age, sex and systolic blood pressure).