The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

MEASUREMENT OF FUNCTIONAL RESIDUAL CAPACITY OF THE LUNG BY PARTIAL CO2 REBREATHING METHOD DURING ACUTE LUNG INJURY IN ANIMALS



Lara Brewer, M.S.1 and Joseph Orr, Ph.D.1


1Anesthesiology, University of Utah, Salt Lake City, Utah, United States.

Background: We measured Functional Residual Capacity (FRC) of the lungs with a CO2 partial rebreathing technique in mechanically ventilated animals before, during, and subsequent to an acute lung injury induced by oleic acid. We compared the FRC from partial CO2 rebreathing with those of a nitrogen washout reference method.

Materials and Methods:
Using an approved animal protocol, general anesthesia was induced and maintained with propofol in six swine (38.8-50.8 kg). A partial CO2 rebreathing monitor (NICO2, Respironics Inc., Wallingford, CT) was placed in the breathing circuit between the endo-tracheal tube and the Y-piece. The partial CO2 rebreathing signal obtained from this monitor was used to calculate FRC using proprietary algorithms. FRC was also measured with a nitrogen washout measurement technique. We collected data from healthy lungs and then subsequent to a lung injury simulating ARDS conditions which was created by intravenously infusing 0.09 ml/kg of oleic acid over a 15-minute period. At each stage of the experiment, the positive end-expiratory pressure (PEEP) was set to 0, 5, 10, and 15 mmHg H2O. At each PEEP level, we compared the average of three FRC measurements from CO2 rebreathing to the average of three nitrogen washout reference measurements.

Results:
The correlation coefficient for the linear regression (Figure) between CO2 rebreathing and nitrogen washout measurements was R = 0.94 (n = 51 data points). The average bias of the measurement was -81 137 mL (mean standard deviation).

Discussion:
These results indicate FRC measurement by CO2 rebreathing can reliably detect a decrease in FRC during lung injury and can reflect the response of the FRC to treatment with PEEP.

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