Abstract
Summary: Positive end-expiratory pressure (PEEP), while of major benefit in the therapy of pulmonary diseases characterized by low functional residual capacity (FRC), is frequently associated with depression of cardiac output (CO) and specific dynamic compliance (Csp). The cardiopulmonary consequences of sequential increases of PEEP (3, 6, 9, 12, 15 cm H2O) in normal dogs were studied utilizing an apparatus that permits measurement of FRC by helium dilution while the animal remains on PEEP. It was found that increasing levels of PEEP had no effect on tidal volume (VT) or inspiratory time, but appeared to lengthen expiratory time by delaying expiratory flow until the preinspiratory period, and led to facilitated expiration. This response occurred immediately upon changes in the level of PEEP and is felt to be reflex in nature. FRC increased and Csp fell as PEEP was increased. This was reflected in a fall in transmission of applied airway pressure to an esophageal balloon. Pulmonary hypertension did not develop in our animals, but net right atrial (RA) pressure was elevated by PEEP. There was no difference in cardiac index (CI) between the control and study groups. Both the magnitude of applied airway pressure and the extent to which it is transmitted across the lungs to the pleural space appear to be determinants of possible effects of PEEP on CO and may explain the diversity of results among reported studies of PEEP. Transmission of pressure is related directly to Csp.
Speculation: Transmission of PEEP to the pleural space is dependent on the level of PEEP and on the preexisting state of the lungs. Transmission of applied airway pressure will be greatest when the Csp of the lungs is highest; it may be reduced significantly if either insufficient or excessive levels are used for a given clinical situation. The pleural pressurevs applied PEEP relationship thus provides a sensitive index of changing status of the lungs, as well as an assessment of therapeutic efficacy.
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Holzman, B., Scarpelli, E. Cardiopulmonary Consequences of Positive End-Expiratory Pressure. Pediatr Res 13, 1112–1120 (1979). https://doi.org/10.1203/00006450-197910000-00006
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DOI: https://doi.org/10.1203/00006450-197910000-00006