Reproduction of inert gas and oxygenation data: a comparison of the MIGET and a simple model of pulmonary gas exchange.

PURPOSE

The multiple inert gas elimination technique (MIGET) is the reference method for evaluating pulmonary gas exchange. MIGET includes a complex experimental method and mathematical model, and has not been used routinely in clinical practice. A simpler mathematical model has been proposed, and was shown previously to fit inert gas data from oleic acid damage. This paper explores the capability of this simple model to describe more complex damage, and to calculate oxygenation data upon changing the inspired oxygen fraction (FIO(2)), comparing these results with those obtained using MIGET.

METHODS

The comparison of oxygenation was done at different ventilator settings and at varying values of FIO(2) in order to mimic the clinical conditions that occur in the intensive care unit.

RESULTS

The simple model describes inert gas data from heterogeneous lung damage within measurement noise. Model simulations performed using the MIGET and the simple model are comparable, the MIGET model simulating partial pressure of oxygen (PaO(2)) values on average 0.22 ± 0.59 kPa (± SD) higher than the simple model. Model simulations are also accurate with a difference between model simulated and measured values of PaO(2) of 0.33 ± 1.48 kPa (± SD) for the MIGET model and 0.12 ± 1.33 kPa (± SD) for the simple model. This comparability and accuracy was similar over different ventilator settings.

CONCLUSIONS

The simple model provides a description of lung damage and arterial oxygenation which is comparable to the MIGET, calculating PaO(2) with acceptable accuracy and precision over the clinically relevant range of PaO(2), and for different values of FIO(2), positive end-expiratory pressure (PEEP), and inspiratory-to-expiratory ratio (I:E).