Smoking status and body size increase carbon monoxide concentrations in the breathing circuit during low-flow anesthesia

The major sources for intraoperative carbon monoxide (CO) in the breathing circuit are related to patient's hemoglobin catabolism, smoking and the deg radation between absorbent and anesthetics. We performed this study to eval uate their combined effects on CO production during low-flow anesthesia. We used a direct-measurement instrument to measure real-time CO concentration s in the breathing circuit during different anesthetic conditions for patie nts who received desflurane or isoflurane. By applying multiple linear regr ession models, we determined the significant factors related to CO concentr ations in the circuit. We identified patients' smoking status, preoperative smoking and body weight as well as gas flow rates as important factors for affecting peak and time-weighted CO levels. These four factors predicted a pproximately 44.1% and 42.7% of peak and mean inspiratory CO concentrations respectively. We found that chronic and preoperative smokers and patients with larger body weights are associated with increased CO concentrations, w hereas increase in gas flow rates could decrease CO concentrations. After c ontrolling these four important factors, we found that inspiratory CO conce ntrations were not significantly associated with the choice of anesthetic a nd its concentration during low-flow anesthesia.