Department of Anesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany.
Crit Care Med. 2013 Mar;41(3):732-43. doi: 10.1097/CCM.0b013e3182711b6e.
Studies correlating the arterial partial pressure of oxygen to the fraction of nonaerated lung assessed by CT shunt yielded inconsistent results. We systematically analyzed this relationship and scrutinized key methodological factors that may compromise it. We hypothesized that both physiological shunt and the ratio between PaO2 and the fraction of inspired oxygen enable estimation of CT shunt at the bedside.
: Prospective observational clinical and laboratory animal investigations.
ICUs (University Hospital Leipzig, Germany) and Experimental Pulmonology Laboratory (University of São Paulo, Brazil). PATIENTS, SUBJECTS AND INTERVENTIONS: Whole-lung CT and arterial blood gases were acquired simultaneously in 77 patients mechanically ventilated with pure oxygen. A subgroup of 28 patients was submitted to different Fio2. We also studied 19 patients who underwent repeat CT. Furthermore we studied ten pigs with acute lung injury at multiple airway pressures, as well as a theoretical model relating PaO2 and physiological shunt. We logarithmically transformed the PaO2/Fio2 to change this nonlinear relationship into a linear regression problem.
We observed strong linear correlations between Riley's approximation of physiological shunt and CT shunt (R = 0.84) and between logarithmically transformed PaO2/Fio2 and CT shunt (R = 0.86), allowing us to construct a look-up table with prediction intervals. Strong linear correlations were also demonstrated within-patients (R = 0.95). Correlations were significantly improved by the following methodological issues: measurement of PaO2/Fio2 during pure oxygen ventilation, use of logarithmically transformed PaO2/Fio2 instead of the "raw" PaO2/Fio2, quantification of nonaerated lung as percentage of total lung mass and definition of nonaerated lung by the [-200 to +100] Hounsfield Units interval, which includes shunting units within less opacified lung regions.
During pure oxygen ventilation, logarithmically transformed PaO2/Fio2 allows estimation of CT shunt and its changes in patients during systemic inflammation. Relevant intrapulmonary shunting seems to occur in lung regions with CT numbers between [-200 and +100] Hounsfield Units.
通过 CT 分流评估动脉血氧分压与非充气肺部分的相关性研究得出的结果不一致。我们系统地分析了这种关系，并仔细研究了可能影响其结果的关键方法学因素。我们假设生理分流和 PaO2 与吸入氧分数的比值都可以在床边估计 CT 分流。
前瞻性观察性临床和实验室动物研究。
德国莱比锡大学医院 ICU 和巴西圣保罗大学实验肺病学实验室。
患者、受试者和干预措施：77 例接受纯氧机械通气的患者同时进行全肺 CT 和动脉血气检查。28 例患者接受不同的 Fio2。我们还研究了 19 例重复 CT 的患者。此外，我们还研究了 10 只患有急性肺损伤的猪，在不同的气道压力下，以及一个将 PaO2 和生理分流联系起来的理论模型。我们对 PaO2/Fio2 进行对数转换，将这种非线性关系转化为线性回归问题。
我们观察到 Riley 生理分流的近似值与 CT 分流之间存在很强的线性相关性（R = 0.84），以及对数转换后的 PaO2/Fio2 与 CT 分流之间存在很强的线性相关性（R = 0.86），这使得我们能够构建一个包含预测区间的查表。在患者内部也观察到了很强的线性相关性（R = 0.95）。通过以下方法学问题，相关性得到了显著改善：在纯氧通气期间测量 PaO2/Fio2，使用对数转换后的 PaO2/Fio2 代替“原始”PaO2/Fio2，将非充气肺部分量化为总肺质量的百分比，并将非充气肺定义为[-200 至+100] Hounsfield 单位间隔，其中包括在不那么不透明的肺区域内的分流单位。
在纯氧通气期间，对数转换后的 PaO2/Fio2 允许在全身炎症期间估计患者的 CT 分流及其变化。在 CT 数介于[-200 和+100] Hounsfield 单位之间的肺区域中，似乎存在相关的肺内分流。
