The multiple inert gas elimination technique (MIGET)

This brief review centers on the multiple inert gas elimination technique (MIGET). This technique, developed in the 1970s, measures the pulmonary exchange of a set of six different inert gases dissolved together in saline (or dextrose) and infused intravenously. It then uses those measurements to compute the distribution of ventilation/perfusion ratios that best explains the exchange of the six gases simultaneously. MIGET is based on the very same mass-conservation principles underlying the classic work of Rahn and Fenn and of Riley and coworkers in the 1950s, which defines the relationship between the ventilation/perfusion ratio and the alveolar and capillary partial pressures of any gas. After a brief history of MIGET, its principles are laid out, its information content is explained, and its limitations are described. It is noted that in addition to quantifying ventilation/perfusion inequality and pulmonary shunting, MIGET can identify and quantify diffusion limitation of O(2) exchange, when present, as well as explain the contributions of extrapulmonary influences such as inspired O(2) concentration, ventilation, cardiac output, Hb concentration/P(50), body temperature and acid/base state on arterial oxygenation. An overview of the technical details of implementing MIGET is given, and the review ends with potential future applications.