EFFECTS OF PEEP ON SYSTEMIC VENOUS CAPACITANCE

The aim of the present study was to determine effects of positive end expiratory pressure (PEEP) application on peripheral venous capacitanc e and relate them to concomitant central hemodynamic disturbances. The venous volume-pressure (V/P) relationships were studied in 6 intact a nesthetized pigs to describe the effects of PEEP on systemic venous co mpliance (computed as the slope of the V/P relationship) and unstresse d volume (referred to as the extrapolated volume intercept). Cardiac v olumes as well as partitioning of circulating blood volume between cen tral (ITBV) and peripheral (PBV) compartments were assessed by thermo- dye dilution techniques. During a 15 cm H2O PEEP application, venous c ompliance was reduced by 48%, while unstressed volume was increased by 25% and peripheral blood pooling increased from 63 to 74%. As a resul t, left heart and right ventricular end diastolic volumes were decreas ed by 8% and by 44%, respectively. It is concluded that increased veno us unstressed volume and reduced compliance depicted the distension of the venous tree secondary to PEEP which acted as apt impediment to ve nous return. As a consequence, cardiac output was reduced because of d ecreased preload.