Volume kinetic analysis of fluid shifts accompanying intravenous infusions of glucose solution.

Volume kinetics is a mathematical tool for macroscopic (whole-body) evaluation of the distribution and elimination of fluid given by intravenous infusion. Although the kinetic system has mostly been applied to crystalloid fluids, such as Ringer's solution, it has more recently been extended to glucose solution, which is characterized by interdependence between glucose and fluid kinetics. The elimination of glucose, as estimated by a one-compartment open model, serves as the driving force for cellular uptake of glucose and, by virtue of osmosis, of water. Key findings include the observation that the infused fluid, besides being accumulated in the cells, occupies a central body fluid space (V1), which is no larger than 3-4 L, and that the cellular hydration has a much longer time-course than the hydration of V1. This explains the risk of hypovolemia associated with rapid infusion of 5% glucose; the dilution of V1, which is quite substantial owing to the small size of this space at baseline, stimulates a brisk diuresis while the excess water is being "trapped" in the cells along with the glucose. Model linearity has been demonstrated for 2.5% glucose solution and this allows the construction of nomograms for administration of such fluid during surgery and critical illness.