Hypocapnia is associated with increased in-hospital mortality and 1 year mortality in acute heart failure patients

Abstract

Aims: Both hypercapnia and hypocapnia are common in patients with acute heart failure (AHF), but the association between partial pressure of arterial carbon dioxide (PaCO₂) and AHF prognosis remains unclear. The objective of this study was to investigate the connection between PaCO₂ within 24 h after admission to the intensive care unit (ICU) and mortality during hospitalization and at 1 year in AHF patients.

Methods and results: AHF patients were enrolled from the Medical Information Mart for Intensive Care IV database. The patients were divided into three groups by PaCO₂ values of <35, 35-45, and >45 mmHg. The primary outcome was to investigate the connection between PaCO₂ and in-hospital mortality and 1 year mortality in AHF patients. The secondary outcome was to assess the prediction value of PaCO₂ in predicting in-hospital mortality and 1 year mortality in AHF patients. A total of 2374 patients were included in this study, including 457 patients in the PaCO₂ < 35 mmHg group, 1072 patients in the PaCO₂ = 35-45 mmHg group, and 845 patients in the PaCO₂ > 45 mmHg group. The in-hospital mortality was 19.5%, and the 1 year mortality was 23.9% in the PaCO₂ < 35 mmHg group. Multivariate logistic regression analysis showed that the PaCO₂ < 35 mmHg group was associated with an increased risk of in-hospital mortality [hazard ratio (HR) 1.398, 95% confidence interval (CI) 1.039-1.882, P = 0.027] and 1 year mortality (HR 1.327, 95% CI 1.020-1.728, P = 0.035) than the PaCO₂ = 35-45 mmHg group. The PaCO₂ > 45 mmHg group was associated with an increased risk of in-hospital mortality (HR 1.387, 95% CI 1.050-1.832, P = 0.021); the 1 year mortality showed no significant difference (HR 1.286, 95% CI 0.995-1.662, P = 0.055) compared with the PaCO₂ = 35-45 mmHg group. The Kaplan-Meier survival curves showed that the PaCO₂ < 35 mmHg group had a significantly lower 1 year survival rate. The area under the receiver operating characteristic curve for predicting in-hospital mortality was 0.591 (95% CI 0.526-0.656), and the 1 year mortality was 0.566 (95% CI 0.505-0.627) in the PaCO₂ < 35 mmHg group.

Conclusions: In AHF patients, hypocapnia within 24 h after admission to the ICU was associated with increased in-hospital mortality and 1 year mortality. However, the increase in 1 year mortality may be influenced by hospitalization mortality. Hypercapnia was associated with increased in-hospital mortality.

Keywords: Acute heart failure; Arterial blood gas; Medical Information Mart for Intensive Care IV; Partial pressure of arterial carbon dioxide.