Over the last 20 years the multiple inert gas elimination technique has been widely used in clinical research in pulmonary and critical care medicine. It has been shown to be useful for improving understanding of the mechanisms of abnormal arterial blood gases in disease states and the effects of different interventions, and also in identifying the various intra- and extrapulmonary determinants influencing PaO2. In patients with acute respiratory distress syndrome and life-threatening
bacterial pneumonia the predominant mechanism of low Pa02 is increased intrapulmonary shunt together with mild to moderate VpJQ abnormalities, which are more conspicuous in the latter condition (Fig 1). In contrast, in patients with respiratory failure secondary to chronic obstructive pulmonary disease or acute severe asthma the major component of abnormal blood gases is VktQ mismatching and intrapulmonary shunt is marginal; in all these conditions inert dead-space is mildly to moderately increased. The role of O2 diffusion limitation is negligible in all these clinical conditions.
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