Plasma cytokine levels in spinal surgery with sevoflurane or total intravenous propofol anesthesia – A post hoc analysis of a randomized controlled trial

•Anesthesia per se does not significantly alter plasma cytokine concentrations.•Plasma IL-6 concentration was increased in all patients after surgery and associated with the duration of surgery.•Sevoflurane anesthesia caused a more pronounced increase in postoperative IL-6 than propofol anesthesia.•There was no significant association between plasma IL-6 and renal function (by plasma creatinine) after surgery.