The present study investigated the hemodynamics, vascular and extravascular volume expansion induced by infusion of lactated Ringer's solution in children and adults before surgery. This was a prospective randomized double‑blind study. A total of 28 patients (14 children and 14 adult patients; American Society of Anesthesiology status I) scheduled for similar minor pelvic, anal rectal or lower limb surgery were recruited for the present study. All patients were administered with 10 ml/kg of lactated Ringer's solution at a constant rate over 20 min. After fluid infusion, plasma dilutions were calculated based on the concentration of hemoglobin. Heart rate (HR), mean arterial pressure (MAP) and urine output were measured before anesthesia was administered for surgery. Results demonstrated that the plasma dilution within 90 min of infusion initiation of lactated Ringer's solution was less pronounced in children compared with adult patients (0.07 vs. 0.16; P<0.001). Children also excreted more of the infused fluid through the kidney within 90 min of infusion initiation than the adults (55% vs. 24%; P=0.01). Following completion of fluid infusion, the volume expansion efficiency was higher in adults [0.82 (0.52‑1.00)] than in children [0.46 (0.26‑0.68)]. The relative changes in HR were significantly greater in children than in adults 15‑60 min after infusion initiation (P<0.01). After 60 min, HRs were comparable between the groups; however, MAP declined significantly from 25‑90 min after infusion initiation in children (P<0.05), yet remained nearly constant in adults (P>0.05). Simple regression analysis revealed a positive relationship between the relative changes in MAP and the plasma dilution, and the reduction in MAP in children was able to explain 47% of the variation in plasma dilution (R2=0.47; P=0.007). In conclusion, different hemodynamics and dynamics of fluid shift of Ringer's solution prior to surgery in children and adults may provide anesthesiologists with new information of how to administer fluid treatment for each patient.

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