PEEP and CPAP

Abstract

Cardiopulmonary effects of positive end-expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) were studied in 12 spontaneously breathing patients who had undergone operative placement of aortocoronary bypass grafts. Catheters were placed for continuous recording of airway, intrapleural, radial artery, pulmonary artery, and pulmonary artery occlusion pressures, and for determination of cardiac output. Samples of radial artery and mixed venous blood were taken for analysis of gas tensions and pH. Measurements permitted calculation of transpulmonary (airway distending) pressure, transmural (effective filling) pulmonary artery occlusion pressure, systemic vascular and pulmonary arteriolar resistances, stroke volume, and pulmonary venous admixture. Measurements and calculations were made while patients received ambient expiratory airway pressure, PEEP, and CPAP. Expiratory transpulmonary pressure was elevated equally by PEEP and CPAP compared with ambient expiratory airway pressure. Respiratory effort was increased by PEEP, but not by CPAP. PEEP and CPAP increased mean intrapleural pressure (p < 0.001). CPAP, but not PEEP, decreased effective cardiac filling pressure (p < 0.001). Stroke volume increased in every patient during spontaneous ventilation with PEEP (p < 0.001), but was unchanged during CPAP.