Canine Left Ventricular Volume Response to Mechanical Ventilation with PEEP

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Abstract
To determine the cause of decreased cardiac output (CO) resulting from the use of PEEP [positive end expiratory pressure], hemodynamic and pulmonary parameters and radiographic estimates of left ventricular volumes were observed in 9 dogs under 3 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 volumes and the left ventricular stroke work index (LVSWI) decreased .apprx. 30% 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. Reduced left ventricular preload apparently is the cause of decreased cardiac output by PEEP and indirect evidence of preload TMLVEDP is not an adequate assessment of the force-length relationship under the conditions stated.