The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

EVALUATION OF CARDIAC OUTPUT MEASUREMENT BY PARTIAL CO2 REBREATHING DURING ACUTE LUNG INJURY IN ANIMALS



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


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

Background: We tested the reliability of cardiac output measurement by partial CO2 rebreathing in injured lungs where the fidelity of etCO2 as an indicator of PaCO2 may be distorted. We compared partial rebreathing cardiac output measurements to bolus thermodilution both in healthy lungs and following an acute lung injury induced by oleic acid.

Materials and Methods:
Using an approved animal protocol, we induced general anesthesia in five swine (38.8-50.8 kg) and placed a pulmonary artery catheter for bolus thermodilution cardiac output measurements. The partial CO2 rebreathing noninvasive cardiac output monitor (NICO2, Respironics Inc., Wallingford, CT) was placed in the breathing circuit between the endo-tracheal tube and the Y-piece. Cardiac output measurements were made with each device every 20 minutes. We collected data in healthy lungs and subsequent to a lung injury that simulated ARDS conditions which was created by intravenously infusing 0.09 ml/kg of oleic acid over a 15-minute period. We compared the average of three bolus thermodilution measurements to the average of the partial CO2 rebreathing measurements taken before and after the thermodilution measurements.

Results:
The correlation coefficient for the linear regression (Figure) between partial rebreathing and the thermodilution cardiac output measurements was r = 0.82 (n = 62 data points). The average measurement error during the healthy lung period was 0.56 0.73 L/min (mean standard deviation) and was 0.53 1.07 L/min following the lung injury.

Discussion:
Our results show accurate cardiac output measurements using partial CO2 rebreathing. We observed little decrease in measurement accuracy during the period of lung injury simulating ARDS.

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