Volume kinetics of Ringer solution after surgery for hip fracture

PURPOSE: To study the time course of volume changes during and after infusion of Ringer's solution in elderly patients after a standardised trauma. METHODS: The kinetics of 12.5 ml.kg-1 Ringer's solution infused over 30 min were studied in ten patients one day after surgery for hip fracture (mean age, 70 yr) and in an age- and sex-matched control group. Hemodilution, as measured every five minutes for 90 min, was used to calculate the size of the fluid space expanded by the fluid (V) and the elimination rate constant (kr). The baseline fluid balance status in the patients and the controls was compared by bioelectrical impedance analysis. RESULTS: The size of V was 4.1 +/- 0.51 (mean +/- SEM) in the patients and 3.4 +/- 0.21 in the controls (P:NS) while the corresponding results for kr were 85 +/- 12 and 166 +/- 27 ml.min-1, respectively (P < 0.04). Bioelectrical impedance analysis showed that the extracellular fluid space and the total body water volumes did not differ between the two groups. Computer simulations based on the data obtained for V and kr indicate that trauma increases the dilution of the plasma volume and the retention of fluid in response to slow and moderate infusion rates, while these indices of short-term changes in fluid balance remain the same in the two groups during very rapid infusion of Ringer's solution. CONCLUSION: A slower elimination rate increased dilution of plasma and retention of fluid when Ringer's solution was infused in elderly trauma patients.