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 O₂ exchange, when present, as well as explain the contributions of extrapulmonary influences such as inspired O₂ concentration, ventilation, cardiac output, Hb concentration/P₅₀, 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.