The Arterial-Alveolar Carbon Dioxide Tension Gradient in Diagnosis of Pulmonary Embolus

Abstract

1. A study designed to examine the utility of the test of arterial-alveolar Pco 2 gradient and of alveolar dead space in recognition of pulmonary embolus is reported. Analyses were carried out in control healthy subjects, in patients with chronic bronchitis with and without emphysema, in cases of documented pulmonary embolus and finally, after balloon occlusion of one mainstem pulmonary artery. 2. Chronic bronchitis with or without emphysema was found to be the greatest drawback to the accuracy of the Pco 2 test in detection of pulmonary embolus. 3. Rapid, shallow breathing due to whatever cause may lead to spuriously low alveolar Pco 2 and falsely positive tests. 4. Extreme caution must be observed in interpreting the results of tests utilizing alveolar Pco 2 . Large emboli may be missed if the embolized areas are under-ventilated. Contrariwise, false positive tests may occur when there is underlying obstructive lung disease and also when samples of the alveolar air are diluted with low-Pco 2 dead space or room air. 5. The test may be relied upon only if the physician is fully aware of the theoretic, as well as practical pitfalls and exerts due caution in its interpretation.