Objective To investigate whether the new oxygenation index [ PaO2 /( FiO2 ×Paw ) ]which including mean airway pressure ( Paw ) for assessing intrapulmonary shunting of acute respiratory distress syndrome( ARDS) could be more accurate than the conventional oxygenation ratio ( PaO2 /FiO2 ) .Methods Twelve patients with ARDS were recruited. All patients received mechanical ventilation under lung ventilation protective strategy ( VT 6 mL/kg, f 16 bpm, FiO2 60% ) , and had a Swan-Ganz catheter inserted. Then, pressure/ volume curves were determined by low-flow method and the lower inflection point pressure was surveyed. Subsequently, parameters of respiratory mechanics and haemodynamics were recorded while periphery and pulmonary artery blood gas analysis were performed when positive end expiratory pressure ( PEEP) were changed. PaO2 /FiO2 and Qsp/Qt were calculated through special formula respectively. Results The progressive PEEP could not change Cst, PaO2 /FiO2 , and PaO2 / ( FiO2 ×Paw) in patients with ARDS significantly ( P gt; 0. 05) . The progressive PEEP did not change Qsp/Qt significantly ( P gt;0. 05) . The Δz which was used to test the difference between the correlation coefficient of Qsp/Qt and PaO2 / ( FiO2 ×Paw) and the correlation coefficient of Qsp/Qt and PaO2 /FiO2 was 0. 571, and there was no difference between the two correlation coefficients ( P gt; 0. 05) . It was not Paw but Cst which impacted on Qsp/Qt and PaO2 /FiO2 . Conclusion PaO2 / ( FiO2 × Paw ) is equal to PaO2 /FiO2 in assessing intrapulmonary shunting of ARDS.
