A method for the measurement of glucose oxidation using the constant infusion of stable isotope

We developed a method to measure the oxidation of glucose using the primed constant infusion of [U-13C] glucose in critically ill patients fed by total parenteral nutrition. The results obtained from the isotopic method were compared to those from indirect calorimetry in the critically ill patients. A patient with esophageal carcinoma was used for the preliminary study. The study was performed on the third postoperative day, assuming severely stressed state. Priming doses of NaH13CO3 at a dosage of 0.32 mg/kg and D-[U-13C] glucose at a dosage of 0.32 mg/kg were injected. D-[U-13C] glucose was then infused at an infusion rate of 0.004 mg/kg/min. It was revealed that the time required for an isotopic plateau was approximately 45 min in plasma glucose and 120 min in an expired air in highly stressed state. Isotopic measurement and indirect calorimetry were performed simultaneously pre- and postoperatively on three patients who underwent surgery for esophageal carcinoma. Increased fat oxidation was obtained by the isotopic method, whereas indirect calorimetry indicated nonprotein RQ above 1.0. Isotopic measurement offered a useful information that cannot be obtained from indirect calorimetry concerning the energy metabolism in the critical illness. Thus our method for the measurement of glucose oxidation is both simple and useful in investigating the energy metabolism in critically ill patients.