| Volatile anesthetics with a difluoromethoxy group ( such as des-flurane, enflurane and isoflurane) can produce carbon monoxide (CO) from carbon dioxide absorbents in anesthesia circuits and this reaction may cause high blood carboxyhemoglobin ( COHb) concentrations intraoperatively. The levels of CO and COHb during anesthesia depend on the volatile anesthetic we used and its concentration, the dryness of the C02 absorbent and its type, the fresh gas flow (FGF) , the subject weight and so on. Several studies showed that a dangerous CO intoxication can occur in small size animal anesthesia, especially with low - flow anesthesia, but the COHb levels have not been studied in children during inhaled anesthesia. Our goal for this study was to e-valuate the reliability of three inhaled anesthesias in children through detecting the COHb concentrations.Materials and MethodsTwenty-four children (ASA I -II , weight 18 ~30kg) who underwent elective surgery and general anesthesia were included in this study, and were allocated randomly to one of three groups according to the volatile anesthetic used and FGF: E500 group (enflurane, FGF500ml/min, n=8), D500 group (desflurane, FGF500ml/min, n = 8), D2000 group (desflurane, FGF2000ml/min, n=8). Soda lime was changed at the night before surgery. At first, intravenous ketamine (2mg/kg) was given and artery was punctured. After indue-tion with fentanyl (0. 002mg/kg) , propofol (2mg/kg) , vecuronium (0.1mg/kg), the children were intubated and ventilated mechanically. Ventilation was adjusted to obtain normocapnia at baseline ( end -tidal carbon dioxide partial pressure of 35 ~40mmHg). At first 15 minutes, FGF was set to 2500ml/min ( O21000ml/min, N20 1500ml/ min). Meanwhile, inhaling anesthetics to make minimum alveolar concentration ( MAC) reached 1.0-1.3 rapidly. After ventilation for 15 minutes, FGF was changed to the designed level, then MAC was kept within 1.0-1.3. Arterial samples were gotten and to be detected by CO - OXYMETER and spectrophotometer before and 30min, 45min, 60mih after ventilation. Blood pressure, pulse, SpO2, respiratory parameters, MAC, and hemoglobin, oxyhemoglobin, COHb concentrations were measured.Results were expressed as mean ± standard deviation ( x ± s). Statistical significance was determined by one - way analysis of variance for repeated measures for intra - group comparisons and student t test for two inter - groups comparisons ( SPSS statistic ) .ResultsThere showed no statistical significance in difference of children s gender, age, body weight, content of hemoglobin before and after operation in 3 groups. The water contents of soda lime we used were 6. 50 ± 0. 32% ( fresh) , 6. 08 ± 0. 38% ( after a night). In D500 group and E500 group, the fractions of inhaled oxygen ( FiO2) decreased gradually, and the FiO2 at the 60min point was much lower than that at the 30min point (P <0. 05) , but not in D2000 group. The basal COHb concentration of children is 2.52 ± 1. 68%. In D500 group and E500 group, the COHb concentrations increased graduallyfrom the 30min point and the value at the 60min point was higher than that of the other points but there was no statistical significance. In D2000 group the highest value was at 45min point. For a given desflu-rane concentration exhaled, the COHb concentration at each point in D500 group had no statistical significance compared with that of the corresponding point in D2000 group. For a given MAC, the COHb concentration of each point in D500 group had no statistical significance compared with that at the corresponding point in E500 group ( P >0.05).DiscussionA difluoromethoxy group is a structural requirement for volatile anesthetics degradation to CO. CO can occupy the oxygen binding sites on hemoglobin and leftward shift of the oxygen - hemoglobin dissociation curve, with consequent reduction in tissue oxygen delivery. But anesthesiologists often neglect the symptom and sign caused by increased COHb during anesthesia.More studies showed that the levels of CO and COHb d...
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