A comparison of the MIGET and a simple model of pulmonary gas exchange

Abstract

The multiple inert gas elimination technique (MIGET) [1] is the reference technique for assessing pulmonary gas exchange, but is not routinely used in clinical practice. The purpose of this study was to assess whether a simpler model of gas exchange, identifiable from clinical data, could simulate the effects of changing ventilator settings on arterial oxygenation in a comparable way to MIGET. Seven pigs were studied prior to and following lung damage with oleic acid, and at a range of ventilator settings. The MIGET and simple models were fitted to inert gas data, as described previously [2], and then used to simulate changes in arterial oxygenation on varying FiO2. Model simulations performed using MIGET and the simple model are comparable, the MIGET model simulating PaO2 values on average 0.22 kPa ± 0.59 (SD) higher than the simple model. Model simulations are also accurate with a difference between model simulated and measured values of PaO2 of 0.33 kPa ± 1.48 (SD) for the MIGET model, and 0.12 kPa ± 1.33 (SD) for the simple model. For oleic acid lung damage, the simple model provides a description of arterial oxygenation which is comparable to the MIGET over the clinically relevant range of PaO2.