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

Abstract

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 24h after admission to the intensive care unit (ICU) and mortality during hospitalization and at 1year in AHF patients. 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 >45mmHg. The primary outcome was to investigate the connection between PaCO2 and in-hospital mortality and 1year mortality in AHF patients. The secondary outcome was to assess the prediction value of PaCO2 in predicting in-hospital mortality and 1year mortality in AHF patients. A total of 2374 patients were included in this study, including 457 patients in the PaCO2<35mmHg group, 1072 patients in the PaCO2=35-45mmHg group, and 845 patients in the PaCO2>45mmHg group. The in-hospital mortality was 19.5%, and the 1year mortality was 23.9% in the PaCO2<35mmHg group. Multivariate logistic regression analysis showed that the PaCO2<35mmHg 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 1year mortality (HR 1.327, 95% CI 1.020-1.728, P=0.035) than the PaCO2=35-45mmHg group. The PaCO2>45mmHg group was associated with an increased risk of in-hospital mortality (HR 1.387, 95% CI 1.050-1.832, P=0.021); the 1year mortality showed no significant difference (HR 1.286, 95% CI 0.995-1.662, P=0.055) compared with the PaCO2=35-45mmHg group. The Kaplan-Meier survival curves showed that the PaCO2<35mmHg group had a significantly lower 1year 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 1year mortality was 0.566 (95% CI 0.505-0.627) in the PaCO2<35mmHg group. In AHF patients, hypocapnia within 24h after admission to the ICU was associated with increased in-hospital mortality and 1year mortality. However, the increase in 1year mortality may be influenced by hospitalization mortality. Hypercapnia was associated with increased in-hospital mortality.