Assessment of in vivo glucose kinetics using stable isotope tracers to determine their alteration in humans during critical illness.

Glucose plays a central role in energy metabolism, and alterations in its utilization have been reported under a variety of physiological and pathological conditions. The extent and direction of its changes provide useful information to promote the understanding of pathophysiology. The regulation of in vivo glucose kinetics is important because it is closely linked to energy production and the control of amino acid and protein metabolism. Although alterations in glucose kinetics have been demonstrated in critically ill patients, the mechanisms responsible are not well understood. The measurement of glucose kinetics in humans using stable isotopic glucose tracers provides a better understanding of the responses to nutritional support in these patients. While tracer methods have been used to quantitatively measure in vivo kinetics in patients with a variety of critical illnesses as well as in normal volunteers during fasting and exercise in European countries and the United States, they have not received the same attention in Japan. Stable isotopic glucose tracers can be safely given to humans since they are themselves naturally occurring substances, accounting for a small percentage of the total, depending on the isotopic species. The intravenous administration of a glucose tracer allows quantitative assessment of in vivo glucose kinetics under a variety of conditions. This method has wide potential for obtaining kinetic data on all aspects of in vivo glucose metabolism, with major advantages for conducting metabolic studies in humans.