Hypoxemic respiratory failure in patients with acute heart failure

The incidence of hypoxemia and the indications for oxygen therapy in patients with acute heart failure (AHF) are not well known.

A large nationwide registry of unselected AHF patients attended in the emergency department (ED) was analysed. Oxygen saturation by pulse-oximetry (SpO₂) was measured on ED arrival, and the ratio SpO₂/F_IO₂ was calculated to adjust for the impact of pre-hospital oxygen therapy, stratifying patients into three groups: normal ratio (≥ 452; corresponding approximately to a SpO₂>94%, on room air), mild decrease of the ratio (429-451; SpO₂~90-94%) and hypoxemia (≤ 428; SpO₂~<90%). Unadjusted and adjusted 30-day all-cause mortality was analyzed by category and restricted cubic spline (RCS).

Of 18,904 AHF patients, 6949 (36.7%) had normal SpO₂/F_IO₂, 5438 (28.8%) showed mild decrease of the ratio, and 6517 (34.5%) were hypoxemic. Hypoxemia was documented in 40% of hospitalized patients and was observed in all phenotypes, ranging from 18.6% in acute decompensated heart failure, to 100% in acute pulmonary oedema. The severity of most physiological parameters, the level of biomarkers, the rate of comorbidities and the 30-day all-cause mortality risk were inversely related to SpO₂/F_IO₂. Mortality risk progressively increased for SpO₂/F_IO₂<452 but became nearly flat when it was<350 suggesting that the prognosis did not depend only on the severity of respiratory failure.

Impaired oxygenation was observed in nearly two thirds of patients with AHF attended in ED. Hypoxemia occurred in 40% of those hospitalized, affecting all phenotypes and was associated with more severity and worse prognosis. This should be considered when addressing treatment recommendations for these patients.