The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

ESOPHAGEAL PRESSURE IS A POOR ESTIMATE OF REGIONAL PLEURAL PRESSURE BUT A FAIR SURROGATE FOR MEAN PLEURAL PRESSURE IN SUPINE DOGS.

McKibben A, Adams A, Goldner M, Marini J.J. Univ. of Minnesota & St. Paul Ramsey Medical Center, Mpls/St. Paul, MN.

Background: Measurement of esophageal pressure (Pes) provides an estimate of pleural pressure (Ppl), allowing determination of transpulmonary pressure (P_{TP}). Assessment of P_{TP} may guide ventilatory strategy to avoid pressure or volume induced lung injury and permits partitioning of respiratory system mechanics into lung and chest wall components. Direct measurement of Ppl would be ideal, but this would require a surgical procedure to place a pressure sensing device within the pleural space. P_{ES} provides a minimally invasive estimate of pleural pressure, although it is susceptible to artifacts and can not reflect the range of pleural pressure. In a study which included direct measurement of regional pleural pressure, we also measured P_{ES} to determine its relation to Ppl. Methods: Eight mongrel dogs were anesthetized and sedated in the supine position. Three specially designed pressure sensing wafers were placed via a right thoracotomy, equally spaced along the fifth intercostal line (ventral, middle, dorsal). The incision was closed and a chest tube evacuated air from the pleural space. A multiperforated esophageal balloon catheter was placed in the usual manner. The ventilator was set to deliver a range of tidal volume at two levels of PEEP (4.8±0.99-LOW and 15.1±0.85 cm H_{2}O-HIGH, mean±1 S.D.) Results: End expiratory values of P_{ES} are compared to Ppl at ventral, middle, and dorsal locations. Values are cm H_{2}O, mean±1 S.D.

P_{ES} Ventral Middle Dorsal Mean Ppl

PEEP Low 5.1±1.9 -1.0±2.1 2.9±2.9 7.3±2.8 3.0±1.6

PEEP High 8.7±1.8 4.1±2.6 7.9±3.7 11.7±2.7 7.9±2.5

Correlation

Coefficient (r^{2}) Ventral Middle Dorsal Mean

P_{ES} 0.4744 0.3126 0.2787 0.500

Conclusions: P_{ES} has a relatively poor correlation with directly measured regional Ppl. The relationship is, however, closest between Pes and the mean Ppl. While esophageal pressure measurement is valuable as a clinically feasible means of sampling Ppl, its limitations must be appreciated, e.g. when estimating Ptp. Because this investigation did not assess Pes during spontaneous respirations, these findings do not directly relate to the use of Pes for determination of the work of breathing.

OF-97-136

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