Variation of venous admixture‚ SF6 shunt‚ Pa−O2‚ and the Pa−O2/F−IO2 ratio with F−IO2

Abstract

Background. Measures of impairment of oxygenation can be affected by the inspired oxygen fraction.Methods. We used a mathematical model of an inhomogenous lung to predict the effect of increasing inspired oxygen concentration (FIO2) on: (1) venous admixture ((Q) over dotva/(Q) over dott); (2) arterial oxygen partial pressure (Pa-O2); (3) the Pa-O2/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.Results. For lungs with regions of low (V) over dot/(Q) over