The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

AGREEMENT BETWEEN RESPIRATORY SYSTEM COMPLIANCE OBTAINED BY TRADITIONAL METHOD VERSUS ESOPHAGEAL PRESSURE MONITORING.

Carl Hinkson, David R. Park, Catherine L. Hough; Respiratory Care - Box 359761, Harborview Medical Center, Seattle, WA

Background: Patients with ARDS may benefit from the use of esophageal pressure monitoring (EPM) to guide ventilator management. Using esophageal pressure (PES) as a surrogate for pleural pressures, end-inspiratory and end-expiratory transpulmonary pressures can be calculated, allowing targeting of tidal volume and PEEP to specific goals. It is unknown if PES is a valid surrogate for pleural pressures during critical illness. We considered that if EPM measurements are representative of pulmonary mechanics then they would agree with a known standard, such as respiratory system compliance (CRS). CRS is available during standard patient-ventilator systems check and can also be calculated from transpulmonary values. We hypothesized that there would be good agreement between the two CRS. Methods: We performed a retrospective review of a convenience sample of patients known to have had EPM, abstracting patient characteristics, ventilator monitoring data, and confirmation of proper placement of esophageal catheter by CXR from the medical record. CRS from EPM was calculated using 1/CRS = 1/ ( VT/ end-inspiratory transpulmonary pressure - end-expiratory transpulmonary pressure) + 1/ (VT/ PES). Data was analyzed from six ventilator checks with complete information for each patient after balloon placement. Agreement was determined by Bland-Altman plot and Kappa (k). Correlation was determined using Pearson correlation (r) Results: Forty-six patients who had EPM were identified; the decision to place the esophageal balloon was made by the physician intensive care team. Ten patients were excluded due to improper balloon placement and three did not have complete data. Agreement between compliance measurements at the first ventilator check was poor; only 9 of 34 measurements were within 10%; (kappa = 0.00). Correlation was modest (r=0.693). The Bland Altman plot demonstrated poor agreement across the range of compliance measurements. Data from remaining ventilator checks were similar. Conclusion: Although correlated, the lack of agreement suggests that EPM CRS and traditional CRS measurements are not interchangeable. More research is needed to support the validity for PES as a surrogate of pleural pressure.
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