The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

How Does PEEP Really Work?

Luciano Gattinoni, MD Monday, November 4, 1996

The ARDS lung: physiopathological and clinical insights from CT scan study.

The adult respiratory distress syndrome (ARDS) is characterized by severe hypoxemia, marked derangements in respiratory mechanics and low lung volume.

Even if many improvements have been obtained with the use of new diagnostic and therapeutic tools, mortality remains excessively high. The use of computed tomography (CT) may help the physicians to better understand non-invasively, the pathophysiology of ARDS and the mechanism of action of different therapeutic maneuvers commonly adopted in clinical practice as mechanical ventilation, positive end-expiratory(PEEP) pressure and prone position.

The lung is homogeneously affected by disease process during the early phase of ARDS. This leads to an homogeneous alteration of the vascular permeability. Consequently, the edema accumulates evenly in all lung regions (non-gravitational distribution). The increased lung weight, through the transmission of hydrostatic forces, however, causes a collapse of the lung regions along the vertical axes (compression atelectasis). At plateau pressure, the pulmonary units reopen, and during the following expiration they stay open, if the applied positive end-expiratory pressure is adequate. PEEP is adequate if it is equal or higher than the hydrostatic forces compressing the unit. Prone position is another maneuver effective in keeping open pulmonary units that were previously collapsed. During late acute respiratory distress syndrome, the compression atelectasis are less present due to edema reabsorption, and the lung undergoes structural changes, usually associated with carbon dioxide retention and development of emphysema-like lesions.

Gattinoni, L.; Pelosi, P.

Isituto di Anestesia e Rianimazione Universita degli studi di Milano, Ospedale Maggiore IRCCS, Milano, Italy

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