Pulmonary Dead Space Fraction and Pulmonary Artery Systolic Pressure as Early Predictors of Clinical Outcome in Acute Lung Injury

Abstract

The primary objective of this study was to test whether an elevated systolic pulmonary artery (PA) pressure or an elevated pulmonary dead space fraction (Vd/Vt) in early acute lung injury (ALI) is associated with poor clinical outcomes in the era of lung-protective ventilation. Prospective observational cohort study. ICUs of a university hospital. Forty-two patients with ALI receiving mechanical ventilation. PA pressure was measured noninvasively using transthoracic echocardiography. Vd/Vt was measured by volumetric capnography (NICO Cardiopulmonary Management System; Novametrix; Wallingford, CT). There was no difference in the mean systolic PA pressure in patients who died compared to those who survived (43 +/- 9 mm Hg vs 41 +/- 9 mm Hg, p = 0.54) [mean +/- SD]. In contrast to the PA systolic pressure, Vd/Vt was significantly higher in patients who died compared to those who survived (0.61 +/- 0.09 vs 0.53 +/- 0.10, p = 0.02). Similarly, Vd/Vt was higher in patients with < 7 ventilator-free days during the first 28 days after enrollment compared to those with > 7 ventilator-free days (0.61 +/- 0.08 vs 0.52 +/- 0.11, p = 0.008). In the era of lung-protective ventilation, systolic PA pressure early in the course of ALI is elevated but not predictive of outcome. However, elevated Vd/Vt in early ALI is associated with increased mortality and with fewer ventilator-free days.