Which of the following can result in an invalid indirect calorimetry measurement?

• A. Enterocutaneous fistula
• B. Chest tube leak
• C. Hemodynamic stability
• D. FiO2 less than 60%

Answer: (B)

Indirect calorimetry determines energy expenditure from measured oxygen consumption and carbon dioxide production, which depends on a sealed or properly controlled gas sampling path without dilution by ambient air. Any intrusion that introduces outside air into the respiratory circuit or sampling line will skew VO2 and VCO2 readings, making the calculated REE unreliable.

A chest tube leak is a situation where ambient air can mix with exhaled gas before analysis, directly diluting the gas sample and biasing the measurements. That is why a chest tube leak can render the indirect calorimetry data invalid.

An enterocutaneous fistula, being a gastrointestinal defect, does not directly affect the respiratory gas sampling. Hemodynamic stability supports reliable measurements rather than undermining them. FiO2 less than 60% is within the typical valid range for many indirect calorimetry devices; it does not by itself invalidate the measurement.