In multi-level lumbar spinal fusion surgery yielding a large amount of blood loss, choice of fluid for volume resuscitation is an important issue since it can influence acid-base status, coagulation, and patients' outcome. This study compared the effect of plasmalyte to 0.9% saline on coagulation assessed by rotation thromboelastometry (ROTEM) and acid-base balance in the aforementioned patients.Fifty patients were randomly allocated to receive either 0.9% saline or plasmalyte during operation and until postoperative 12 h. ROTEM was performed at 10 min after anesthetic induction and end of surgery. Arterial blood gas analyses were serially performed from 10 min after anesthetic induction until postoperative 12 h. Fluid balance, blood loss, and transfusion requirement were assessed.ROTEM variables showed sporadic deterioration in both groups after surgery without intergroup differences. Intraoperatively, arterial pH, base excess, and bicarbonate concentrations were lower and serum chloride concentrations were higher in the 0.9% saline group compared with the plasmalyte group. The differences in base excess and bicarbonate concentrations persisted until postoperative 12 h. Fluid balance, blood loss, and transfusion requirement were similar between the groups while urine output was greater in the plasmalyte group compared with the 0.9% saline group (3.2 ± 1.6 ml/kg/h vs. 1.8 ± 1.1 ml/kg/h, p = 0.001).In contrast to plasmalyte, fluid therapy with 0.9% saline resulted in transient hyperchloremic acidosis in patients undergoing multi-level lumbar spinal fusion, while coagulation assessed by ROTEM analysis and the amount of blood loss were similar between the groups.