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

Aims Both hypercapnia and hypocapnia are common in patients with acute heart failure (AHF), but the association between partial pressure of arterial carbon dioxide (PaCO 2 ) and AHF prognosis remains unclear. The objective of this study was to investigate the connection between PaCO 2 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 PaCO 2 values of <35, 35–45, and >45 mmHg. The primary outcome was to investigate the connection between PaCO 2 and in‐hospital mortality and 1 year mortality in AHF patients. The secondary outcome was to assess the prediction value of PaCO 2 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 PaCO 2 < 35 mmHg group, 1072 patients in the PaCO 2 = 35–45 mmHg group, and 845 patients in the PaCO 2 > 45 mmHg group. The in‐hospital mortality was 19.5%, and the 1 year mortality was 23.9% in the PaCO 2 < 35 mmHg group. Multivariate logistic regression analysis showed that the PaCO 2 < 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 PaCO 2 = 35–45 mmHg group. The PaCO 2 > 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 PaCO 2 = 35–45 mmHg group. The Kaplan–Meier survival curves showed that the PaCO 2 < 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 PaCO 2 < 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.