Volume kinetics of intravenous crystalloid and colloid solutions in healthy, isoflurane-anesthetized rabbits

Objective: To investigate the feasibility of characterizing fluid disposition-including potency, distribution, and elimination-of different IV fluids in healthy, isoflurane-anesthetized rabbits using microconstant volume kinetic analysis. Methods: In this prospective, randomized crossover study, 10 rabbits were anesthetized and received 25 mL/kg of lactated Ringer solution (LRS) and 6.25 mL/kg of 6% tetrastarch 130/0.4 solution (HES), each infused IV over 20 minutes, with a washout period of at least 14 days between treatments. Serial measurements of hemoglobin concentration, RBC count, and Hct were obtained at preestablished time points and served as input variables for volume kinetic analysis. Results: The prescribed doses of LRS and HES produced similar peak plasma dilutions, consistent with the convention that colloids are approximately 4 times more potent than isotonic crystalloids. The distribution and elimination half-lives of LRS were approximately 4.6 and 57.8 minutes, respectively, whereas those of HES were approximately 53.5 and 231.0 minutes. Conclusions: Volume kinetic analysis is a feasible method to characterize fluid disposition in anesthetized rabbits. The potency, distribution, and elimination of LRS and HES in healthy, isoflurane-anesthetized rabbits align with previously reported data in other mammalian species. However, further studies incorporating urine volume measurements are warranted. Clinical Relevance: Intravenous HES demonstrates greater fluid potency and longer intravascular persistence than LRS in healthy, isoflurane-anesthetized rabbits.