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

The Cardiovascular Research Institute, the Departments of Medicine and Anesthesia and the Adult Echocardiography Laboratory, University of California, San Francisco

Michael.matthay{at}ucsf.edu

Abstract

Study Objective: The primary objective of this study was to test whether an elevated systolic pulmonary artery pressure or an elevated pulmonary dead-space fraction in early acute lung injury is associated with poor clinical outcomes in the era of lung-protective ventilation.

Design: Prospective observational cohort study.

Setting: Intensive care unit of a university hospital.

Patients: 42 mechanically ventilated patients with acute lung injury.

Measurements: The pulmonary artery pressure was measured non-invasively using transthoracic echocardiography. The pulmonary dead-space fraction was measured by volumetric capnography using the NICO^® monitor.

Main results: There was no difference in the mean systolic pulmonary artery pressure in patients who died compared to those who survived (43 ± 9 mmHg versus 41 ± 9 mmHg, p = 0.54). In contrast to the pulmonary artery systolic pressure, the pulmonary dead-space fraction was significantly higher in patients who died compared to those who survived (0.61 ± 0.09 versus 0.53 ± 0.10, p = 0.02). Similarly, the dead-space fraction was higher in patients with less than 7 ventilator-free days during the first 28 days after enrollment compared to those with more than 7 ventilator-free days (0.61 ± 0.08 versus 0.52 ± 0.11, p = 0.008).

Conclusion: In the era of lung-protective ventilation, systolic pulmonary artery pressure early in the course of acute lung injury is elevated but not predictive of outcome. However, elevated pulmonary dead-space fraction in early acute lung injury is associated with increased mortality and with fewer ventilator-free days.

Key Words: Acute lung injury • acute respiratory distress syndrome • systolic pulmonary artery pressure • transthoracic echocardiography • pulmonary dead-space fraction