Pulmonary dead space fraction and pulmonary artery systolic pressure as early predictors of clinical outcome in acute lung injury

Study objective: The primary objective of this study was to test whether an elevated systolic pulmonary artery (PA) pressure or an elevated pulmonary dead space fraction (V-D/V-T) in early acute lung injury (ALI) is associated with poor clinical outcomes in the era of lung-protective ventilation. Design: Prospective observational cohort study. Setting: ICUs of a university hospital. Patients: Forty-two patients with ALI receiving mechanical ventilation. Measurements: PA pressure was measured noninvasively using transthoracic echocardiography. V-D/V-T was measured by volumetric capnography (NICO Cardiopulmonary Management System; Novametrix; Wallingford, CT). Main results: 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, V-D/V-T 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, V-D/V-T 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). Conclusion: 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 V-D/V-T in early ALI is associated with increased mortality and with fewer ventilator-free days.