A Fluid Challenge Test for the Diagnosis of Occult Heart Failure

A right heart catheterization with measurements of pulmonary artery wedge pressure (PAWP) may be necessary for the diagnosis of left heart failure as a cause of pulmonary hypertension or unexplained dyspnea. Diagnostic cutoff values are a PAWP of ≥ 15 mm Hg at rest or a PAWP of ≥ 25 mm Hg during exercise. However, accurate measurement of PAWP can be challenging and heart failure may be occult. Left heart catheterization, with measurement of left ventricular end-diastolic pressure, may also be indecisive. Measurements are then best repeated in stress conditions. Exercise is an option, but the equipment is not universally available, and interpretation can be difficult in patients with wide respiratory pressure swings. An alternative is offered by a fluid challenge. Studies have gathered data supporting infusion of 500 mL or 7 mL/kg saline and a PAWP of 18 mm Hg as a diagnostic cutoff. The procedure is simple and does not take much catheterization laboratory time. Combining echocardiography with invasive measurements may increase the diagnostic accuracy of diastolic dysfunction. Cardiac output after a fluid challenge may be of prognostic relevance.