Tehran University of Medical Sciences Archives of Anesthesiology and Critical Care 2423-5849 6 2 2020 05 04 78 82 Omid Azimaraghi Department of Anesthesiology and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Arash Heroabadi Department of Anesthesiology and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Alireza Saliminia Department of Anesthesiology and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Reza Atefyekta Department of Anesthesiology and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Peyman Saberian Department of Anesthesiology and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Hojat Dehghanbanadaki Students' Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran. Noushin Khazaei Department of Anesthesiology and Critical Care Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Ali Movafegh Department of Anesthesiology and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2019 10 25 2019 12 18 Background: Goal-directed fluid therapy may improve perioperative fluid management. This study aimed to evaluate the effects of Pleth variability index (PVI)-guided fluid therapy on changes in intraoperative serum lactate levels in comparison with liberal fluid therapy. Methods: This study was a randomized double-blinded clinical trial that was conducted in the operating room of a university hospital. Inclusion criteria comprised patients aged 18–60 years and classified as American Society of Anesthesiologists physical status class I and II, who were candidates for elective thyroidectomy. In total, 44 patients meeting the inclusion criteria were enrolled in the study and randomly assigned to two groups: the liberal and PVI groups. In both groups, 5 mL/kg bolus of normal saline was infused prior to the anesthesia induction. In the PVI group, 100 mL bolus of normal saline was administered every 5 min if the PVI remained >13% during the operation. In the liberal group, continuous crystalloid infusion (5–6 mL/kg/h) was administered throughout the surgery. Arterial blood samples were taken, and serum lactate levels were measured following anesthesia induction and just before tracheal extubation. Results: In the PVI group, mean serum lactate decreased at the end of the surgery, with a difference of −0.6 ± 0.13 mmol/L, whereas it increased in the liberal group (0.070 ± 0.3, P<0.05). Conclusion: In conclusion, we found that using intraoperative PVI-guided fluid therapy could decrease serum lactate levels and total fluid administration compared to the liberal method. https://aacc.tums.ac.ir/index.php/aacc/article/view/267