Objectives: To observe the effect of different fresh gas flows (FGF) on carboxyhemoglobin (COHb) levels non-invasively and continuously and to determine the contribution of the smoking status to intraoperative carbon monoxide (CO) accumulation and respiratory complications.,Methods: A total of 64 patients were included in the study. Carboxyhemoglobin level was monitored non-invasively from the fingertip. Patients were divided into 2 according to the FGF as low-flow anesthesia (LFA; Group L) and high flow anesthesia (Group H). Each group was divided again into 2 groups as smokers and non-smokers. Carboxyhemoglobin and and the respiratory complications that occurred in the post-anesthesia care unit were recorded.,Results: The mean COHb values were significantly higher in Group L between 30th and 210th minutes. Furthermore, in Group L, intraoperative COHb levels were significantly higher in smokers compared to non-smokers in all periods. In group H, no difference was observed between smokers and non-smokers in terms of COHb levels after 60 minutes and also preoperative COHb levels of the patients developed respiratory complication was higher.,Conclusion: If the CO2 absorbent is properly preserved in patients who are administered LFA, there will be no risk of CO accumulation even in chronic smokers.