Canine Left Ventricular Volume Response to Mechanical Ventilation with PEEP

To determine the cause of decreased cardiac output (CO) resulting from the use of PEEP, hemodynamic and pulmonary parameters and radiographic estimates of left ventricular volumes were observed in nine dogs under three conditions: control, PEEP (15 cm H2O), and PEEP with intravascular (IV) volume expansion. Volume expansion was sufficient to return the CO to control values. Cardiac index (CI), stroke volume index (SI), left ventricular stroke work index (LVSWI) all decreased approximately 30 per cent with the application of PEEP. Ejection fraction remained unchanged. With IV volume expansion, the CI, SI, left ventricular end-diastolic volume index, and LVSWI returned to approximate control values. The transmural left ventricular end-diastolic pressure (TMLVEDP) did not change significantly. The authors therefore conclude that reduced left ventricular preload is the cause of decreased cardiac output by PEEP and that indirect evidence of preload (transmural left ventricular end-diastolic pressure) is not an adequate assessment of the force-length relationship under the conditions stated.