Pulmonary embolism in the patient with chronic obstructive pulmonary disease. A diagnostic dilemma.

It is often difficult to distinguish pulmonary embolism from worsening underlying disease in the setting of severe chronic obstructive lung disease. We describe three patients with severe COPD and angiographically documented pulmonary embolus to stress that standard clinical and radioisotopic studies were of little value in establishing a diagnosis. All patients had acute increases in alveolar ventilation immediately following the embolus with a reduction in previously elevated levels of PaCO2, as well as hypoxemia. Such changes in arterial blood gases in the patient with severe COPD should suggest pulmonary embolus rather than increased obstruction.