In order to visualize pulmonary vascular drainage and to assess its influence on measurements obtained by Swan-Ganz catheters in the wedge position, 75 patients were examined with a portable chest x-ray after injection of water soluble contrast medium into a Swan-Ganz catheter in the wedge position. In normal patients and patients with left-sided cardiac failure, the pulmonary vein draining the wedged segment was easily visualized. However, in many patients with sepsis and ARDS, the pulmonary vein was poorly visualized or not visualized. In some of these patients, there was a high pulmonary wedge pressure. It is hypothesized that in some of these patients, the competitive flow system between the pulmonary and bronchial circulation is upset due to a decrease in flow through pulmonary vessels and either relative or absolute increase in bronchial flow in the segment distal to the balloon. This increase in the ratio of bronchial to pulmonary blood flow results in dilution of the contrast medium by the nonopacified bronchial blood.
The decreased pulmonary blood flow may be due to a vasospastic factor in either the small pulmonary arterioles or venules as, in two cases, the pulmonary vein was visualized after injection of vasodilators.
In order to eliminate these misleading false high wedge pressures (WP) in these types of patients, the authors recommend that wedged Swan-Ganz catheter angiograms be performed in selective cases. If the pulmonary vein is not visualized and there is elevation of the pulmonary WP, this must not be taken as a sign of elevated left-sided cardiac pressure. If the pulmonary vein is visualized, the WP measured can be considered to reflect the left-sided cardiac pressure.