Volume Kinetics for Infusion Fluids

Volume kinetics is a method for analyzing and simulating the distribution and elimination of infusion fluids. Approximately 50 studies describe the disposition of 0.9% saline, acetated and lactated Ringer´s solution, based on repeated measurements of the hemoglobin concentration and (sometimes) the urinary excretion. The slow distribution to the peripheral compartment results in a 50-75% larger plasma dilution during an infusion of crystalloid fluid than would be expected if distribution had been immediate. A drop in the arterial pressure during induction of anesthesia reduces the rate of distribution even further. The renal clearance of the infused fluid during surgery is only 10-20% compared to conscious volunteers. Some of this temporary decrease can be attributed to the anesthesia and probably also to preoperative psychological stress and/or dehydration. Crystalloid fluid might be allocated to “non-functional” fluid spaces where it is unavailable for excretion. This amounts to approximately 20-25% during minor (thyroid) surgery