The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

PRONE POSITION INCREASES DORSAL TRANSPULMONARY PRESSURE IN NORMAL DOGS.

Adams AB, Shapiro RS, Goldner M, Marini JJ. Regions Hospital, St. Paul, MN.

Background: Atelectasis and radiographic abnormalities in adult respiratory distress syndrome (ARDS) are predominantly gravity-dependent (dorsal). By increasing transpulmonary pressure (Ptp), PEEP recruits lung units, thus reducing shunt and improving oxygenation. Prone positioning also improves oxygenation in a majority of patients with ARDS. We reasoned that prone positioning decreases dorsal Ppl disproportionately creating a regional PEEP-like effect. To determine dorsal Ptp, a measure of regional Ppl is needed since esophageal pressure may reflect overall rather than dorsal Ppl.

Methods: Wafers sensing lung surface pressure were affixed via right thoracotomy to the dorsal and ventral pleural lining in 4 ventilated, ancsthetized, and paralyzed mongrel dogs. In three dogs, end expiratory Ppl was measured in the supine and prone positions. To simulate and amplify the potential effect of lung edema, the same measurements were made in one dog after the lungs were filled to FRC with perflubron (S.G. = 1.93)

Results: Pressures in cmH_{2}O:

Air-filled (n=3, means) Supine Prone [DELTA] Ptp

Ventral -5.5 2.9 8.4

Dorsal -0.6 -4.7 4.1

Liquid-filled (n=1)

Ventral -7.5 6.5 14.0

Dorsal 6.0 -8.2 14.2

Dorsal Ptp increased in the prone position by 4.1 cmH_{2}O in normal lungs and by 14.2 cmH_{2}O in fluid-filled lungs due to decreases in dorsal pleural pressure. Conclusions: The prone position may cause a regional increase in Ptp that exerts traction on those areas most susceptible to atelectasis. This "regional PEEP" could be an important mechanism for increased oxygenation seen in prone positioning and the effect may be amplified by the presence of alveolar fluid. Supported by SCOR HL50512.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

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