The influence of positive end-expiratory pressure on intrapericardial pressure and cardiac function after coronary artery bypass surgery.

The hemodynamic effects of positive end-expiratory pressure (PEEP) were studied in coronary artery bypass patients by recording intrapericardial and intracardiac pressures, measuring cardiac output by thermodilution, and determining left ventricular volumes by nuclear radiography. An elevation of PEEP to 5, 10, and 15 cm H2O led to a decrease in cardiac output (15% decrease at PEEP 15) as intrapericardial pressure increased and transmural left atrial pressure decreased. Modest volume loading (an increase in left atrial pressure of 3 mm Hg) greatly attenuated the deleterious effects of 15 cm H2O PEEP. There was an excellent correlation between pulmonary capillary wedge pressure and left atrial pressure at PEEP 0 and 5 (r = .85 and r = .83). This correlation was not nearly as reliable at PEEP 15 (r = .54). A predictable increase in intrapericardial pressure was observed as PEEP was applied in these patients. The magnitude of this increase can be estimated by multiplying the change in PEEP (in cm H2O) by 0.4 to estimate the change in intrapericardial pressure (in mm Hg). Using this estimation as a guide, modest volume loading can be used to maintain transmural filling pressures (and cardiac output) when PEEP is used after coronary artery bypass surgery.