A clinical comparison of indices of pulmonary gas exchange with changes in the inspired oxygen concentration

摘要: Several indices have been introduced as convenient alternatives to calculation of the physiological shunt fraction (Qs/QT) for assessment pulmonary gas exchange. These include: arterial-alveolar oxygen tension ratio (a/APO2), arterial tension-inspired concentration (PaO2/FIO2), respiratory index (RI), [A-a)DO2/PaO2) and alveolar-arterial difference [A-a)Do2). are in use clinically despite fact that they may not accurately predict exchange situations where FIO2, Qs/QT or arterial-venous content is changing. The clinical stability each these indices, relative behaviour shunt, was therefore investigated prospectively ten mechanically ventilated postoperative adults FIO2 varied from 0.30 1.00. None studied reliably reflected shunt. As increased incrementally 1.00, 42 55 per cent measured changes were opposite direction corresponding maximum magnitudes substantial; 24 22 a/APO2 PaO2/FIO2 respectively, 67 RI 101 (A-a)DO2. We conclude any a patient's defect when varying can be substantially misleading.