Background: Acute Heart Failure (AHF) is a potentially lethal pathology and is often encountered in the prehospital setting. Although an association between prehospital arterial hypercapnia in AHF patients and admission in high-dependency and intensive care units has been previously described, there is little data to support an association between prehospital arterial hypercapnia and mortality in this population.

Methods: This was a retrospective study based on electronically recorded prehospital medical files. All adult patients with AHF were included. Records lacking arterial blood gas data were excluded. Other exclusion criteria included the presence of a potentially confounding diagnosis, prehospital cardiac arrest, and inter-hospital transfers. Hypercapnia was defined as a PaCO2 higher than 6.0 kPa. The primary outcome was in-hospital mortality, and secondary outcomes were 7-day mortality and emergency room length of stay (ER LOS). Univariable and multivariable logistic regression models were used.

Results: We included 225 patients in the analysis. Prehospital hypercapnia was found in 132 (58.7%) patients. In-hospital mortality was higher in patients with hypercapnia (17.4% [23/132] versus 6.5% [6/93], p = 0.016), with a crude odds-ratio of 3.06 (95%CI 1.19-7.85). After adjustment for pre-specified covariates, the adjusted OR was 3.18 (95%CI 1.22-8.26). The overall 7-day mortality was also higher in hypercapnic patients (13.6% versus 5.5%, p = 0.044), and ER LOS was shorter in this population (5.6 h versus 7.1 h, p = 0.018).

Conclusion: Prehospital hypercapnia is associated with an increase in in-hospital and 7-day mortality in patient with AHF.