Effects of different fresh gas flow rates in carboxyhemoglobin formation daring desflurane anesthesia / 中华麻醉学杂志

ABSTRACT

Objective Desflurane is now well accepted by anesthesiologists because of its rapid induction and recovery but carboxyhemoglobin(CUHb) formation from interaction of desflurane with soda lime is a major concern. The purpose of this study was to investigate the effects of different fresh gas flow(FGF) rates on COHb formation during desflurane anesthesia. Methods Forty ASA Ⅰ-Ⅱ nonsmoking patients undergoing elective surgery were randomly divided into four groups with ten patients in each group according to FGF rate group Ⅰ 0.5L/min; groupⅡ 1.0L/min; group Ⅲ 2.0L/min; group Ⅳ4.0L/min. The patients were premedicated with pethidine 1mg/kg and atropine 0.01mg/kg. Anesthesia was induced with midazolam 0.05mg/kg, propofol 2mg/kg and fentanyl 7pg/kg. Intubation was facilitated with succinylcholine. Anesthesia was maintained with desflurane( 1 .5 MAC), nitrous oxide( 50%) and intermittent vecuronim and fentanyl. PET CO2 was maintained between 35-40 mmHg. Venous blood samples were taken before and 2h, 4h and 6h after induction of anesthesia and at the end of operation for determination of COHb level. Results There was no significant difference among the four groups in age, gender and weight. COHb concentration was not significantly different before and 2h after induction of anesthesia among the four groups, but increased significantly at 4h and 6h after induction of anesthesia and at the end of surgery in groupⅣ, and tended to increase as the operation was prolonged. It was found that patients who developed postoperative headaehe and PONV were mostly from group IV, but no patients developed delayed neuropsychologic sequelae. Conclusions COHb level increases with high FGF rate but not with low FGF rate because of dryness and higher temperature of soda lime. Fresh soda lime should not be left in Canister too long and should be replaced shortly before anesthesia.