INFLUENCE OF MIXED VENOUS PO-2 AND INSPIRED O-2 FRACTION ON INTRAPULMONARY SHUNT IN PATIENTS WITH SEVERE ARDS

In 12 patients undergoing extracorporeal membrane oxygenation for trea tment of severe acute respiratory distress syndrome (ARDS), we examine d the effects of independent variations in mixed venous oxygen tension (P ($) over bar v(o2)) and inspired oxygen fraction (FIo2) on the dis tribution of ventilation and perfusion as assessed by the multiple ine rt gas elimination technique. Reducing the oxygen concentration of the constant gas stream through the membrane lungs allowed us to decrease the P ($) over bar v(o2) by similar to 20 Torr independently of varia tions in cardiac output and FIo2 as well as to augment FIo2 without in fluencing P ($) over bar v(o2). The interventions did not induce any c hange in heart rate or systemic or pulmonary hemodynamics. In general, neither during mechanical ventilation at FIo2 of 0.6 nor during mecha nical ventilation at FIo2 of 1.0 did the reduced P ($) over bar v(o2) cause variations in the distribution of pulmonary blood flow in our pa tients with severe ARDS. Nevertheless, in individual patients, decreas ing P ($) over bar v(o2) or ventilation at FIo2 of 1.0 was associated with changes in intrapulmonary shunt. Therefore, we conclude that it i s not possible to predict the influence of such interventions in pulmo nary gas exchange in the individual patient suffering from ARDS. Diffe rences in the regulation of the local distribution of blood flow cause d by the disease itself might explain this phenomenon.