The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

IN A SWINE PLEURAL EFFUSION MODEL, FUNCTIONAL RESIDUAL CAPACITY (FRC)CAN BE DETERMINED BY A NITROGEN WASHIN-WASHOUT METHOD DURING MECHANICAL VENTILATION

Jeronimo Graf1, Alex B. Adams1, David Dries1, Arnoldo Santos1, Joseph Tashjian2, John Marini1; 1Pulmonary Research, Regions Hospital, St. Paul, MN; 2Radiology, Regions Hospital, St. Paul, MN

Purpose: The monitoring of FRC in ventilated patients, if available, could evaluate an effect on the lungs of a pleural effusion. Changes in FRC could also reveal the propagation/retreat of a pneumonia when gas exchange data is unavailable or deceptive. In a radiology suite, computerized tomography (CT) can accurately measure FRC. An online nitrogen washin/washout (NWW) method that adjusts FIO2 from .5 to .6 to .5 while inferring nitrogen concentration changes has been developed to measure FRC in ventilated patients. Methods: In a deeply anesthetized swine model, a catheter was inserted into the right chest for saline instillation to create a pleural effusion. In the CT suite we measured FRC concurrently by CT and NWW methods under conditions of PEEP = 0, 10 cmH2O and pleural effusion with 0, 400, 800 ml of saline injected into the pleural space via the inserted catheter. Results: FRC measures from 31 simultaneous observations found a mean difference between the techniques of 23 ml or 7.1%. Both techniques tracked, in parallel, the expected FRC-increasing effects of PEEP and decreases in FRC as a pleural effusion was created. Gas exchange data did not necessarily track with the FRC changes. Conclusion: FRC measurements from CT studies verified the accuracy of an online NWW-FRC technique under varying PEEP and pleural effusion conditions. No problems were encountered that would preclude use of the NWW-FRC technique under other settings or conditions. Implications for Translation into Practice: The effect of a pleural effusion (or pneumonia) on lung volume status can be determined by FRC measurements during mechanical ventilation. Sponsored Research - We have use of the GE carestation ventilator for this FRC comparison study as well as support from GE support for other specific projects in our lab.

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