What is important about FiO2 during measurement of indirect calorimetry?

What is important about FiO2 during measurement of indirect calorimetry?

• A. It should vary during measurement
• B. It should remain constant during the measurement
• C. It should be high as possible
• D. It should be low as possible

Answer: (B)

The main idea is that FiO2 must stay constant during indirect calorimetry because the calculation of energy expenditure depends on fixed inputs for inspired oxygen. Indirect calorimetry determines oxygen consumption and carbon dioxide production from the differences between inspired and expired gas concentrations. If the fraction of inspired oxygen changes during the measurement, the inputs to these calculations change independently of the body's metabolic rate, biasing VO2 and VCO2 and leading to an inaccurate estimate of energy expenditure. Maintaining a steady FiO2 helps achieve a true metabolic steady state and makes the gas-exchange measurements reliable. If supplemental oxygen is used, it should be delivered at a stable, known FiO2, and the measurement should be performed after values have stabilized. The key point is the constancy of FiO2, not the level being high or low.

The main idea is that FiO2 must stay constant during indirect calorimetry because the calculation of energy expenditure depends on fixed inputs for inspired oxygen. Indirect calorimetry determines oxygen consumption and carbon dioxide production from the differences between inspired and expired gas concentrations. If the fraction of inspired oxygen changes during the measurement, the inputs to these calculations change independently of the body's metabolic rate, biasing VO2 and VCO2 and leading to an inaccurate estimate of energy expenditure. Maintaining a steady FiO2 helps achieve a true metabolic steady state and makes the gas-exchange measurements reliable. If supplemental oxygen is used, it should be delivered at a stable, known FiO2, and the measurement should be performed after values have stabilized. The key point is the constancy of FiO2, not the level being high or low.