[Arterio-alveolar difference in CO2 (AaDCO2) : measurement, interpretation, clinical value].

The measurement of arterio-alveolar difference in CO2, easily performed, gives the percentage of non perfused ventilated pulmonary zones. The clinical value of this examination is illustrated by two observations. Its situation, among other tests of the respiratory function, is questioned particularly when the diagnosis of pulmonary embolism is concerned.