BACKGROUND: Lactic acidosis is considered an early sign of propofol infusion syndrome. In this study, we investigated the changes in lactate and pH with propofol versus volatile anesthesia (VA) of long duration. METHODS: Demographic and intraoperative data were recorded retrospectively from the anesthesia records of patients who underwent elective spine surgery longer than 8 h. Propofol patients were matched 1:2 to VA patients, based on anesthesia time (AT) (+/-30 min) and blood loss (BL) (+/-500 mL). RESULTS: Of 246 patients identified, 50 received propofol (AT = 10 +/- 2 h, BL = 1955 +/- 1409 mL) and were matched to 100 VA cases (AT = 10 +/- 1 h, BL = 1801 +/- 1543 mL), and of those, 40 and 72 patients, respectively, had complete lactate data at baseline and at 8 h after anesthesia and were included in the main analysis. The propofol group received 8.8 +/- 2 mg x kg(-1) x h(-1) of propofol. The VA group age was older than the propofol group (58 +/- 12 vs 51 +/- 15 yr, respectively, P = 0.002), but there was no difference between the groups in gender, ASA grade, intraoperative hemodynamic variables, and use of vasopressors. After 8 h, the VA group had a larger increase in arterial lactate from baseline compared with the propofol group (change from baseline: propofol, 0.48 +/- 0.72 mmol/L; VA, 1.2 +/- 1.2 mmol/L, P = 0.001). CONCLUSIONS: During prolonged spine surgery >8 h, VA was associated with higher serum lactate, when compared with propofol infusion. Prospective studies are needed to elucidate the exact mechanisms and clinical implications of this finding.