Whiteley J P, Gavaghan D J, Hahn C E W
Nuffield Department of Anaesthetics, University of Oxford, Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE, UK.
Br J Anaesth. 2002 Jun;88(6):771-8. doi: 10.1093/bja/88.6.771.
Measures of impairment of oxygenation can be affected by the inspired oxygen fraction.
We used a mathematical model of an inhomogenous lung to predict the effect of increasing inspired oxygen concentration (FIO2) on: (1) venous admixture (Qva/Qt); (2) arterial oxygen partial pressure (PaO2); (3) the PaO2/FIO2 index of hypoxaemia; and (4) sulphur hexafluoride (SF6) retention (often taken to be true right-to-left shunt). This model predicts whether or not atelectasis will occur.
For lungs with regions of low V/Q, increasing the inspired oxygen concentration can cause these regions to collapse. In the absence of atelectasis, the model predicts that Qva/Qt will decrease and arterial oxygen partial pressure increase as FIO2 is increased. However, when atelectasis occurs, Qva/Qt rises to a constant value, whilst PaO2 falls at first, but then begins to rise again, with increasing FIO2. The SF6 retention increased markedly in some cases at high FIO2.
Venous admixture will estimate true right-to-left shunt at high FIO2, even when oxygen consumption is raised. This model can explain the way that the Pa/Fl ratio changes with increasing inspired oxygen concentration.
氧合受损的测量指标可能会受到吸入氧分数的影响。
我们使用非均匀肺的数学模型来预测增加吸入氧浓度（FIO₂）对以下方面的影响：（1）静脉血掺杂（Qva/Qt）；（2）动脉血氧分压（PaO₂）；（3）低氧血症的PaO₂/FIO₂指数；以及（4）六氟化硫（SF₆）潴留（常被视为真正的右向左分流）。该模型可预测是否会发生肺不张。
对于存在低V/Q区域的肺，增加吸入氧浓度会导致这些区域塌陷。在不存在肺不张的情况下，模型预测随着FIO₂升高，Qva/Qt会降低，动脉血氧分压会升高。然而，当发生肺不张时，Qva/Qt会升至一个恒定值，而PaO₂起初会下降，但随后随着FIO₂升高又开始上升。在某些情况下高FIO₂时SF₆潴留会显著增加。
即使氧耗增加，在高FIO₂时静脉血掺杂也会估计真正的右向左分流。该模型可以解释Pa/Fi比值随吸入氧浓度增加而变化的方式。
