Volume kinetics of Ringer's solution in female volunteers

The kinetics of crystalloid solutions in humans have not been adequatelydescribed previously. Therefore, we measured blood haemoglobinconcentration during and for 120 min after i.v. infusion of 25 ml kg-1 ofRinger's acetate solution over 15, 30, 45 and 80 min, and 12.5 ml kg-1 over30 min in six adult female volunteers. The dilution- time profiles wereanalysed according to a new kinetic model adapted for fluid spaces. Volumeexpansion produced by Ringer's solution approached steady state in anexponentially decaying manner when plasma volume had increased byapproximately 550 ml. The size of the fluid space expanded by Ringer'ssolution was only 4.8 litre (95% confidence interval 3.8-5.8 litre) exceptfor the fastest infusion, where it averaged 9.0 litre. The rate of fluidelimination could be predicted as the product of plasma dilution and aconstant averaging 95 (95% confidence interval 68-122) ml min-1.