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The salutary Effects of Positive End Expiratory Pressure (PEEP) in Experimentally Induced Pseudomonas Pneumonia

Paul G. Barash, MD^*, Martin C. Bunke, MD, M. David Tilson, MD, Jonathan D. Katz, MD, Leslie H. Cronau, MD, PhD, and Arthur E. Baue, MD

*Associate Professor of Anesthesiology; Director of Surgical Intensive Care Unit. Departments of Anesthesiology and Surgery, Yale University School of Medicine, New Haven, Connecticut 06510 Associate Professor of Surgery. Departments of Anesthesiology and Surgery, Yale University School of Medicine, New Haven, Connecticut 06510 Associate Professor of Anesthesiology. Departments of Anesthesiology and Surgery, Yale University School of Medicine, New Haven, Connecticut 06510 Professor and Chairman of Department of Surgery. Departments of Anesthesiology and Surgery, Yale University School of Medicine, New Haven, Connecticut 06510

Abstract

Controlled data on the effects of positive end expiratory pressure (PEEP) in the presence of Gram negative pneumonia are unavailable. The present study was carried out to examine the cardiopulmonary response to PEEP in dogs before and after the intratracheal inoculation of an inoculum of Pseudomonas aeruginosa (1 x 1O⁹ organisms/kg). Thereby allowing us not only to study the cardiopulmonary response to PEEP in the presence of Gram negative pneumonia, but also the effect of PEEP on the course of the experimentally induced pneumonia. Sixteen mongrel dogs were anesthetized (pentobarbital, pancuronium), intubated, and ventilated (16 ml/kg and 10 respirations/min) for 24 hours with 50% O₂ and 50% N₂O. Half of the animals were maintained with zero end expiratory pressure (ZEEP) and the remainder had PEEP =10 cm H₂O. Half of the dogs in each group were challenged with live Pseudomonas and the following were measured (0, 1, 2, 4, 8, 12, 16, and 24 hours): blood pressure, pulse rate, pulmonary artery pressure, pulmonary capillary wedge pressure, respiratory rate, effective compliance minute ventilation, tidal volume, pH, Pa_co2, Pa_co2, P_o2, cardiac output, and hematocrit.

Three of four infected ZEEP dogs died before 24 hours; all infected animals treated with PEEP and control dogs survived. The infected ZEEP dogs developed a significantly (p < 0.05) elevated cardiac index as early as 4 hours, accompanied by a significant increase in venous admixture; oxygenation and compliance deteriorated profoundly. Infected ZEEP dogs also showed signs of early capillary leak with a 50% increase in mean hematocrit, despite the infusion of 63% more fluid (13.3 ml/kg/hr) than the control group to maintain a pulmonary capillary wedge pressure of 8 mm Hg. Cardiovascular and respiratory function in the infected PEEP group was not markedly different from the noninfected PEEP or ZEEP control animals.

The results indicate a conspicuous advantage of PEEP over ZEEP in experimentally induced Pseudomonas pneumonia, not only in terms of improved cardiopulmonary function, but also in terms of early survival.

Key Words: VENTILATION: positive end-expiratory pressure • COMPLICATIONS: pneumonia • LUNG: pneumonia

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999