Pulmonary dead space monitoring: Identifying subjects with ARDS at risk of developing right ventricular dysfunction

Abstract

BACKGROUND: ARDS is a highly morbid condition characterized by diffuse pulmonary inflammation, which results in hypoxemic respiratory failure. Approximately 25% of patients with ARDS develop right ventricular dysfunction, with cor pulmonale being a common final pathway in a significant number of non-survivors. ARDS-related right ventricular dysfunction occurs due to acute elevation in ventricular afterload caused by mechanisms that are associated with increased pulmonary dead space fraction. Thus, we hypothesized that changes in pulmonary dead space fraction may reflect changes in pulmonary hemodynamics. METHODS: This was a prospective single-center study of 21 subjects with ARDS who underwent serial determination of pulmonary dead space fraction and pulmonary hemodynamics via transthoracic echocardiography. Linear mixed-effects modeling was performed to test for an association between a change in pulmonary dead space and a change in pulmonary hemodynamics. RESULTS: The tricuspid regurgitation velocity to right ventricular outflow track velocity time integral ratio, an echocardiographic surrogate for pulmonary vascular resistance, increased by 0.16 Wood units (Coefficient 0.16, 95% CI 0.09–0.23; P < .001), and the tricuspid regurgitation pressure gradient increased by 3.7 mm Hg (Coefficient 3.7, 95% CI 1.74–5.63, P < .001) for every 10% increase in pulmonary dead space fraction. CONCLUSIONS: Increases in the pulmonary dead space fraction were associated with relative increases in both the tricuspid regurgitation velocity to right ventricular outflow track velocity time integral ratio and the tricuspid regurgitation pressure gradient, which likely contributed to the high incidence of ARDS-related right ventricular dysfunction encountered in clinical practice. Pulmonary dead space monitoring may serve as a clinical indicator to identify patients with ARDS at risk of developing right ventricular dysfunction and acute cor pulmonale.