[Methods of interpreting pulmonary gas exchange].
When arterial and mixed venous blood gas tensions, inspired and expired O2 and expired CO2 concentrations are known, it is possible to calculate the alveolar-arterial PO2 difference, intrapulmonary right-to-left shunt and dead space ventilation. However, because arterial hypoxemia is caused by ventilation/perfusion mismatching in most cases, a method allowing analysis of ventilation/perfusion ratios is needed. The "multiple inert gas elimination technique" (MIGET) is a powerful method that is useful for this purpose. This technique is based on measurements of arterial, venous and expired levels of inert gases spanning a wide range of solubility and analysis of the lung for the ventilation/perfusion ratios from true shunt to dead space ventilation. True shunt, with ventilation/perfusion ratios of 0, can be differentiated from ventilation/perfusion ratios of 0.005, and dead space ventilation can be distinguished from ventilation/perfusion ratios over 10 and under 100. Ventilation/perfusion ratios between these extremes can also be differentiated. It is not unusual for results yielded by MIGET to differ from those obtained with O2-dependent methods: O2 shunt generally exceeds MIGET shunt, for example, because O2 shunt includes low ventilation/perfusion units.
Schaffartzik
W
W
Klinik für Anaesthesiologie und operative Intensivmedizin, Freie Universität Berlin.
D000818:Animals; D001249:Asthma / Q000503:physiopathology; D004285:Dogs; D006801:Humans; D016210:Methacholine Chloride; D008722:Methods; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D014692:Ventilation-Perfusion Ratio / Q000502:physiology
D016210:Methacholine Chloride