A computer model of gas exchange during cardiopulmonary resuscitation

This paper presents a computer model of gas exchange during cardiopulmonary resuscitation (CPR) that permits independent adjustment of inspired air content (16% O2 and 4.5% CO2 present in mouth-to-mouth (MTM) ventilation or ambient air), shunt, deadspace, diffusion impairment, cardiac output, and ventilation. The model contains 15500 acini, each with its own blood supply. Gas exchange occurs at each perfused and ventilated acinus. Arterial P(O2) and P(CO2) are calculated from the summed arterial blood flow using standard formulae. The model and simulations show that MTM ventilation provides inadequate oxygenation when the victim is at high altitude or has diffusion impairment. They also show that analysis of inspired and expired gas concentrations to measure gas exchange primarily measures wash in and wash out of gas when cardiac output is low and that this explains the negative oxygen consumption and carbon dioxide production measured in a previous study.