Critical Care and Shock

Effects of airway pressure release ventilation on extra vascular lung water in acute lung injury and acute respiratory distress syndrome


Background: Extra Vascular Lung Water plays an important role in the pathophysiology of Acute Lung Injury and Adult Respiratory Distress Syndrome, and correlates with oxygenation and survival. Our trial is testing the hypothesis that Airway Pressure Release Ventilation reduces the EVLW (primary endpoint) in ALI/ARDS patients through the increase in the mean airway pressure paralleling the improvement in oxygenation (secondary endpoint).

Methods: A pilot study to test the effect of APRV on the EVLW in patients with ALI/ARDS compared to conventional mechanical ventilation. EVLW was measured by the thermodilution method using the PiCCO2 system. Measurements were done on conventional ventilation, after 1 and 6 hours from switching to APRV. Six patients with the diagnosis of ALI/ARDS < 72 hours were enrolled during a 3 months period.

Results: Results are reported in mean ± SD, and statistical analysis is done with one way multi-measurement ANOVA. P value of 0.05 was considered significant. Regression analysis was used to test the correlation between variables. EVLWI was significantly reduced by 24 % (19.6 ± 7.5 to 15 ± 4.1) in 1 hour and 11 % (17.5 ± 6) in 6 hours, P value: 0.017. The mPaw was significantly increased by 68 % (15.8 ± 5.5 to 26.5 ± 4.7) in 1 hour and by 55 % (24.5 ± 3.8) in 6 hours, P value: 0.004. PaO2/FiO2 was increased by 47 % (163.6 ± 67.6 to 239.8 ± 132.4) in 1 hour and 68% (275.8 ± 165.3) in 6 hours, P value: 0.064. The mPaw/EVLWI index was significantly increased by 114 % (0.87 to 1.86) in 1 hour and by 76% (1.53) in 6 hours, P value: 0.015. Strong relations were found between mPaw and EVLWI (R = 0.85), mPaw and PaO2/FiO2 (R = 0.88), EVLWI and PaO2/FiO2 (R = 0.99), mPaw/EVLWI Index and PaO2/FiO2 (R = 0.79).

Conclusion: APRV reduced EVLW, and improved PaO2/FiO2. Mean airway pressure may play an important role in the reduction of EVLW and improvement in oxygenation during APRV. Reduction of EVLW improves oxygenation in ALI/ARDS.