The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts

ACCURACY OF RESTING ENERGY EXPEDITURE CALCULATED BY A MODIFICATION OF THE ABBREVIATED WEIR EQUATION IN MECHANICALLY VENTILATED ADULT ICU PATIENTS.

Mark S. Siobal1, Hanna Hammoudeh1, Michael Snow2; 1Anesthesia, SFGH/UCSF, San Francisco, CA; 2Medical Graphics Corporation, St. Paul, MN

Background: Resting energy expenditure (REE) can be determined by indirect calorimetry using a metabolic analyzer and calculation by the abbreviated Weir equation whereby: REE = [3.9 (VO2) + 1.1 (VCO2)] 1.44. By substituting the measured VCO2 / 0.85 for the measured VO2, REE based on VCO2 (REE CO2) can be calculated without measuring VO2 directly when the respiratory quotient (RQ) is equal to 0.85. We compared REE and REE CO2 measured by the CCM Express metabolic analyzer in mechanically ventilated ICU patients to determine accuracy of the REE CO2 calculation. Method: Results from routine metabolic studies in 67 medical and surgical ICU patients receiving mechanical ventilation were reviewed retrospectively. Data from a total of 116 measurements were compared. All studies were performed when the patient’s FIO2 was between 0.35 and 0.60. The measured RQ ranged between 0.73 and 1.1. Studies were performed using the manufacturers standardized procedure. The review of patient data was approved by the Committee on Human Research at the University of California San Francisco. Results: The correlation between REE and REE CO2 was very strong (r = 0.99, r squared = 0.98). Bias and precision was -15 ± 126 kcal / 24 hrs by Bland – Altman analysis. There was a distinct pattern of agreement when the difference of REE and REE CO2 were compared to RQ whereby as RQ approached 0.70 the percent error (mean bias / mean REE for the range of RQ) became more positive and as RQ approached 1.0 the percent error became more negative. Conclusion: There was strong agreement between REE and REE CO2 measured by the CCM Express metabolic analyzer. Further study is required to determine if the accuracy of the REE CO2 measurement is maintained when performed at FiO2 > 0.60 and if volumetric CO2 measurements of VCO2 can be used to accurately calculated REE CO2 without measuring VO2. Sponsored Research - Medical Graphics Incorporated was consulted regarding study design