Misleading "pulmonary wedge pressure" after pneumonectomy: its importance in postoperative fluid therapy

Patients who have undergone pneumonectomy are reported to be at increased risk of serious pulmonary edema. Monitoring fluid therapy using the Swan-Ganz balloon-tipped catheter is therefore important in the perioperative management of these patients. Pulmonary artery occlusion pressure (PAOP), determined by inflating a balloon to occlude a branch of the pulmonary artery, is routinely used to measure pulmonary wedge pressure (PWP). In turn, PWP reflects left atrial pressure (LAP). We clinically observed postpneumonectomy patients in whom pulmonary edema developed, but whose PAOP was near normal. Our findings led us to suspect that PAOP in such patients may reflect a falsely low PWP value. We hypothesized that after pneumonectomy inflation of the balloon on the Swan-Ganz catheter to obtain PWP can result in considerable occlusion of the remaining cross-sectional area of pulmonary circulation. This occlusion acutely increases the right ventricular afterload, resulting in reduced cardiac output and reduced LAP. Although the PAOP under these circumstances still accurately reflects the LAP, these values have been artificially lowered; hence, they result in falsely low PWP readings. To verify this hypothesis, the following canine experiments were performed. Five dogs were monitored with a Swan-Ganz catheter, a left atrial catheter, and an electromagnetic flow probe applied to a carotid artery. Before pneumonectomy, inflation of the balloon to obtain PAOP caused no statistically significant change in LAP or carotid flow, and PAOP was identical to both LAP and PWP. (PWP was determined by advancing and wedging the pulmonary artery catheter tip into a peripheral branch without inflating the balloon.(ABSTRACT TRUNCATED AT 250 WORDS)