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Background: Although hyperoncotic albumin may be used to recruit oedema, its effectiveness remains unclear. Therefore, this issue was studied during infusion experiments in healthy volunteers.Method: Fifteen healthy volunteers (mean age 31 years) received an infusion of 3 mL/kg of 20% albumin over 30 minutes. Their urinary excretion was recorded, and venous blood samples were taken to measure blood haemoglobin (Hb), haematocrit, colloid osmotic pressure as well as plasma albumin and sodium concentrations on 15 occasions over a period of 300 minutes. Plasma volume expansion was taken as the inverse of the fluid-induced dilution of venous plasma, as given by the blood Hb concentration. Mass balance calculations were used to estimate the mobilisation of fluid from the tissues.Results: Maximum plasma volume expansion was reached 20 minutes after completing an infusion of 20% albumin. Urinary excretion was effectively increased, and the mobilised fluid from the tissues at 300 minutes amounted to 3.4 ± 1.2 mL for each infused mL of 20% albumin, of which 19% was of intracellular origin. The urinary excretion correlated strongly with the amount of recruited fluid (R2  = 0.87) and inversely with the plasma volume expansion (R2  = 0.53).Conclusion: The infusion of 20% albumin significantly increases the plasma volume by recruiting interstitial fluid. After completing the infusion, there is a delay of 20 minutes until maximum plasma dilution is reached, and the duration of the plasma volume expansion lasts far beyond 5 hours. [ABSTRACT FROM AUTHOR]

Background: Crystalloid fluid requires 30 min for complete distribution throughout the extracellular fluid space and tends to cause long-standing peripheral edema. A kinetic analysis of the distribution of Ringer's acetate with increasing infusion rates was performed to obtain a better understanding of these characteristics of crystalloids.Methods: Data were retrieved from six studies in which 76 volunteers and preoperative patients had received between 300 ml and 2375 ml of Ringer's acetate solution at a rate of 20-80 ml/min (0.33-0.83 ml/min/kg). Serial measurements of the blood hemoglobin concentration were used as inputs in a kinetic analysis based on a two-volume model with micro-constants, using software for nonlinear mixed effects.Results: The micro-constants describing distribution (k12) and elimination (k10) were unchanged when the rate of infusion increased, with half-times of 16 and 26 min, respectively. In contrast, the micro-constant describing how rapidly the already distributed fluid left the peripheral space (k21) decreased by 90% when the fluid was infused more rapidly, corresponding to an increase in the half-time from 3 to 30 min. The central volume of distribution (V(c)) doubled.Conclusion: The return of Ringer's acetate from the peripheral fluid compartment to the plasma was slower with high than with low infusion rates. Edema is a normal consequence of plasma volume expansion with this fluid, even in healthy volunteers. The results are consistent with the view that the viscoelastic properties of the interstitial matrix are responsible for the distribution and redistribution characteristics of crystalloid fluid. [ABSTRACT FROM AUTHOR]