An Arterial Blood Gas Diagram for Clinical Use

¹ Pulmonary Disease Service, Letterman General Hospital, San Francisco

A simple diagram for arterial blood gas tensions was constructed from values obtained from normal volunteers at rest, during voluntary breath-holding and during maximal voluntary hyperventilation. Thus, an appropriate arterial oxygen tension (PaO₂) was established for any physiologic level of alveolar ventilation, as reflected by the arterial carbon dioxide tension (PaCO₂). Blood gas tensions of 177 ambulatory patients with differing clinical types of pulmonary insufficiency were plotted against the diagram and the magnitude of the observed deviations from the normal range were compared to selected pulmonary function test results. The vast majority of test results exhibited lower oxygen tensions than predicted from the observed PaCO₂. This actual-predicted PaO2 difference was directly related to the severity of airways obstruction in chronic obstructive pulmonary disease and to the severity of restriction in interstitial lung diseases. Patients in the early stages of lung disease had resting hypocarbia before the onset of hypoxemia or of significant pulmonary function test abnormality. The diagram provides a simple, repid clinical method of diagnosing and estimating the severity of the blood gas disturbances which reflest V/Q mismatching at any physiologic level of alveolar ventilation.