Final answer:
Mechanical ventilation with FiO2 >= 60% can decrease the accuracy of an indirect calorimetry study by interfering with respiratory measurements. Hyperventilation and exercise can also impact the metabolic rate, thus affecting the study's results.
Step-by-step explanation:
The accuracy of an indirect calorimetry (IC) study can be decreased by a few factors. Notably, the use of mechanical ventilation with a fraction of inspired oxygen (FiO2) equal to or greater than 60% can introduce errors. Furthermore, anything that alters the patient's metabolic rate, such as hyperventilation or exercise, can impact the results of an IC study.
It's worth noting that holding routine nursing care or activities during the study, and making measurements in a quiet, thermoneutral environment, can increase rather than decrease the accuracy of the study. To ensure reliability, the individual's nutrient intake should be stable for the previous 12 hours before the test.