Assessment of Nutrient Absorption in Enterally Fed Post-intensive Care Unit Patients Using Bomb Calorimetry: do the Calories Stick

Detailed daily tracking of the enteral feeding provided to each patient, inclusing the type and amount of nutritional formula administered. Apart from the enteral intake, supplemental calories provided by infusion (e.g. glucose) will be recorded to ensure accurate measurement of caloric intake.

"* a nonabsorbable blue dye marker will be administered at the start and end of the stool collection period to precisely indentify the stool produced within a specific time frame.~* stool will be collected for three days. Each sample will be collected, weighted and labeled with the date and time, then stored at -20°C.~* only stool samples from the appearance of the first dye marker to the appearance of the second dye marker will be saved and analyzed.~* bomb calorimetry preparation~ * blending and dilution: each stool sample will be put into a blender and mixed with an equal amount of water~ * freeze dying: the diluted stool will be placed into freeze-dye flasks and frozen at -20°C. The next day, the flasks will be placed into a freeze dryer for 48hours.~ * pellet formation: the freeze-dried samples will be formed into 1-gram pellets and stored until calorimetry~ * calorimetry analysis: the Parr 6200 isoperibol calorimeter will be used to measure the energy content of the stool pellets"

performing indirect calorimetry to measure the REE of each patient