Effect of age on volume kinetic parameters in healthy volunteers receiving Ringer's lactate solution

Understanding the effects of age and body weight on volume kinetics may provide practical guidance for fluid administration in clinical practice. This study aimed to quantify the effects of age and body weight on the volume kinetic parameters in healthy volunteers with varying ages and body weights.

Eighteen healthy volunteers were enrolled in this study. These volunteers received 40 ml/kg of Ringer's lactate solution for 60 min; for safety reasons, volunteers aged > 65 years received 30 ml/kg. The maximum amount of administered fluid was limited to 3600 ml. Venous blood samples were collected at preset intervals to determine the hemoglobin concentrations and hematocrit percentage. NONMEM 7.5 (ICON PLC) was used to perform the population-based volume kinetic analysis.

A total of 122 plasma dilution data points were used from 18 volunteers to determine the pharmacokinetic characteristics of Ringer's lactate solution. Distribution and elimination could be well explained using a two-volume model. The central volume of distribution at baseline (Vc0) and the distributional clearance (kt) between the central and peripheral compartments decreased as age increased. A difference in elimination clearance (kr) was observed based on age, with a value of 60 years (≥ 60 y: 50.2 ml/min; < 60 y: 156 ml/min). Body weight was not a significant covariate for the volume kinetic parameters.

These findings can serve as reference data for determining the appropriate amount of Ringer's lactate solution to administer to patients of different ages in clinical practice.