Prediction of arterial oxygen partial pressure from intrapulmonary venous admixture

A short program was developed to predict the PaO2 at a given FIO2 by using arterial and mixed venous blood gas data obtained at an FIO2 of 1.0. Our program resolves Adair's equation and the shunt equation inversely, on the assumption that intrapulmonary venous admixture and the arteriovenous oxygen content difference remain constant during the study. The study was conducted on 19 patients with respiratory failure who were intubated and mechanically ventilated. According to linear regression analysis, regression coefficients of 0.91 and 0.97 were obtained between the measured PaO2 values and those estimated by the arterial/alveolar oxygen tension ratio (PaO2/PaO2) and our program, respectively (n = 23). The PaO2 values were predicted more accurately by our program than those calculated by PaO2/PaO2. Because our program is simple enough to be carried out with a pocket computer, it may be helpful in a bedside decision of lowering FIO2, especially in patients who require a high FIO2 level to maintain sufficient arterial oxygenation.