Arterial hypoxemia is a common finding in acute pulmonary embolism, its severity generally assumed to be proportional to the extent of pulmonary artery obstruction. We studied blood gases (during room air breathing 100% oxygen breathing) hemodynamic data in seven patients with massive pulmonary embolism circulatory failure. All measurements were made before 30 minutes after medical therapy of shock. We observed that a low cardiac output state can result in a misleading improvement in arterial oxygenation during massive pulmonary embolism, that an improved circulatory status resulting from medical therapy (including inotropic drug infusion with or without blood volume expansion) can paradoxically increase arterial hypoxemia.
We conclude that severity of arterial hypoxemia may not reflect the severity of pulmonary artery obstruction in acute pulmonary embolism if shock is present.