氧合指数对急性呼吸窘迫综合征肺内分流的判定价值

Value of PaO_2/FiO_2 in Reflecting the Intrapulmonary Shunting of Acute Respiratory Distress Syndrome

目的研究氧合指数(PaO2/FiO2)用于反映急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)的肺内分流(Qsp/Qt)准确度下降程度。方法符合ARDS诊断标准患者12例,气管插管呼吸机支持,采用肺保护性通气策略(Vt6ml/kg),留置Swan-Ganz导管,采用低流速法测定准静态肺压力-容积曲线。逐步调整PEEP水平,观察血流动力学、呼吸力学的变化,分别留取外周及肺动脉血行血气分析,分别计算Qsp/Qt和PaO2/FiO2,对结果进行回归分析。结果①Qsp/Qt和PaO2/FiO2两者之间存在线性相关,但决定系数r2只有0.432,相关性偏小;②Qsp/Qt(%)的多元回归方程:y=56.542-3.371x1-0.056x2+0.594x3+2.84x4,x1为PaO2/FiO2,x2为Hgb,x3为PAWP,x4为CI,校正r2=0.538,(P<0.01)。结论用PaO2/FiO2测算ARDS的Qsp/Qt精确度下降,决定系数r2只有0.432,Qsp/Qt除外PaO2/FiO2还受Hgb、肺动脉楔压(plumonary artery wedge pres-sure,PAWP)及心脏指数(cardiac index,CI)等影响。

Objective To study how did the accuracy of the oxygenation index （PaO2/FiO2） reflecting the intrapulmonary shunting （Qsp/Qt） of acute respiratory distress syndrome reduce. Methods Twelve patients who had ARDS were recruited to the study. All required mechanical ventilation,which used lung ventilation protective strategy （Vt6ml/kg） , and had a Swan - Ganz catheter. Then, P - V curves were determined by low - flow method. Subsequently, the parameters of respiratory mechanics and haemodynamics and the blood gas analysis results of periphery and pulmonary artery blood samples were recorded when the conditions of positive end expiratory pressure changed. PaO2/FiO2 and Qsp/Qt were respectively calculated through special formula. Finialy, all data were progressed regression analysis. Results ①There was linear correlation between Qsp/Qt and PaO2/FiO2 , and the coefficient of determination （ R square） was 0. 432 which was significantly smaller （P 〈 0.01 ）. ②The multiple regression equation of Qsp/Qt（ % ） was y = 56. 542 -3. 371x1 -0. 056x2 ＋ 0. 594x3 ＋ 2.84x4,in which x1 was PaO2/FiO2, x2 was haemoglobin, x3was pulmonary wedge pressure, x4was cardiac index, and the adjusted R square was 0. 538 （ P 〈 0.01 ）. Conclusion The accuracy of the intrapulmonary shunting of acute respiratory distress syndrome simply estimated by PaO2/FiO2 further dropped,because r^2 was only 0. 432 and Qsp/Qt was simuhaneously affected by haemoglobin, pulmonary wedge pressure and cardiac index.