Models for an Anesthesia Breathing Circuit

This paper presents a mathematical model of a semi-closed anesthesia breathing circuit. The model comprises four perfect-mixing compartments (corresponding to the lung, the reservoir bag, and the two absorber cannisters), together with four tubes through which gas flows without mixing (corresponding to the inspiratory tube, the expiratory tube, the arm leading to the reservoir bag, and the anatomical dead space). For simplicity, only the case of spontaneous breathing is considered, and only three species of gases are included, namely oxygen, nitrogen, and carbon dioxide. The model’s predictions are compared with experiment, and some of the parameters are adjusted to get a better fit. The resulting model is used to compare the effectiveness of different denitrogenation protocols. Two appendices contain discussions of technical details and modifications needed to include other gases.