What factor during hemodialysis can alter indirect calorimetry measurements?

• A. CO2 loss through the dialysis coil
• B. Increased oxygen consumption by tissues
• C. Temperature fluctuations in the room
• D. Removal of urea

Answer: (A)

Indirect calorimetry estimates energy expenditure from O2 consumption and CO2 production. During hemodialysis, CO2 can diffuse from the blood into the dialysate and be removed by the dialysis circuit. This extra CO2 loss is not due to the body's metabolism and lowers the measured CO2 output, biasing the respiratory quotient and the calculated energy expenditure. The other factors mentioned don’t affect the gas exchange measurement through the dialysis circuit in the same direct way.