Clinical Impact of Different Crystalloid Solution on Early Biomarkers of Kidney Injury After Lumbar Fusion Surgery in Elderly Patients

Patients in this arm receive sodium acetate Ringer's solution as the intraoperative crystalloid fluid for management during elective lumbar fusion surgery under general anesthesia. The fluid administration protocol is standardized as follows: (1) initial volume loading of 5-10 mL/kg within 30 minutes after anesthesia induction; (2) maintenance infusion at 5-7 mL/kg/h; and (3) replacement of blood loss at a crystalloid-to-blood loss ratio of approximately 3:1. Infusion rates are adjusted based on stroke volume variation and hemodynamic parameters. The assigned crystalloid solution is also used as the carrier fluid for any required vasoactive medications. This arm is compared against a control arm receiving sodium lactate Ringer's solution. The target population consists of elderly patients (aged 65-80 years) scheduled for lumbar fusion surgery.

Patients in this arm receive sodium lactate Ringer's solution as the intraoperative crystalloid fluid for management during elective lumbar fusion surgery under general anesthesia. The fluid administration protocol is identical to that of the experimental arm: (1) initial volume loading of 5-10 mL/kg within 30 minutes after anesthesia induction; (2) maintenance infusion at 5-7 mL/kg/h; and (3) replacement of blood loss at a crystalloid-to-blood loss ratio of approximately 3:1. Infusion rates are adjusted based on stroke volume variation and hemodynamic parameters. The assigned crystalloid solution is also used as the carrier fluid for any required vasoactive medications. This arm serves as the active comparator against sodium acetate Ringer's solution. The target population consists of elderly patients (aged 65-80 years) scheduled for lumbar fusion surgery.