Inhalation anesthesia with sevoflurane during thyroid surgery: the low-flow or minimal-flow anesthesia?

Aim ? to study the consumption of an inhalation anesthetic and to compare of clinical and economic components during using of the low-flow anesthesia or the minimal flow anesthesia by sevoflurane in hyperthyroidism patients undergoing thyroidectomy in a specialized centre of endocrine surgery. Materials and methods. All patients were divided into 2 groups: in a group of ?sevoflurane balanced analgesia? (BA-S) were included 35 patients, in a group ?sevoflurane control group? (C-S) were included 46 patients. All patients with thyrotoxicosis were undergoing thyroidectomy under general anesthesia with mechanic ventilation and using of the low- flow anesthesia (LFA) or the minimal flow anesthesia (MFA) by sevoflurane. In the groups BA-S was used LFA with the fresh gas flow FGF=500 ml/min for 25 patients (subgroup C-SLFA), with FGF=700 ml/min for 21 patients (subgroup C-SLFA-0,7). We evaluated the consumption of sevoflurane by Dion's equation and Biro's equation by assessing the vaporizer dial concentration in percent, FGF in liters/minute and time for which the concentration was set in minutes. We calculated the cost of anesthesia as a cost of average doses of sevoflurane and expendable materials that were used during anesthesia. Results and discussion. The sevoflurane consumptions by Dion's equation were 6,25±0,23 ml for the BA-S group, 6,77±0,26 ml for the subgroup of C-SFLA and 8,04±0,32ml for the subgroup of C-SLFA-0,7 and were not significant (p<0,05) more than in Biro's equation, where The sevoflurane consumptions were 5,81±0,24 ml for the BA-S group, 6,37±0,27 ml for the C-SFLA subgroup and 7,52±0,34 ml for the C-SLFA-0,7 subgroup, respectively. Between the values of sevoflurane consumption by Biro's and Dion's equations there is a strong direct correlation on Spearman's correlation coefficient (rs). For the group of CA-C rs=0,87, for C-SLFA rs=0,86, for C-SLFA-0,7 rs=0,84. The sevoflurane consumption was significantly (p<0,05) lower on the criterion of Wilkinson in the BA-S group under MFA with FGF=400 ml/min, as compared to the control subgroups C-SLFA and C-SLFA-0,7, which were used FGF=500 ml/min and 700 ml/min during LFA respectively. In the BA-S group MFA has been demonstrated pharmacy-economic benefits, which were amounted to 100,3±4,1 UAH and 107,8±4,0 UAH for both equations, Biro's and Dion's, respectively. These rates were significantly (p<0,05) lower on the criterion of Wilcoxon in the BA-S group than in the control subgroups C-SLFA and C-SLFA-0,7, where applied LFA with FGF=500 ml/ min and 700 ml/min, respectively. Conclusions. Both, Biro's method and Dion's equation allow us to estimate the sevoflurane anesthesia consumption. Between the equations there is a strong positive correlation, there is no significant difference between the results of the calculations. In our point of view, Dion's equation for assessment of volatile anesthetic consumption reflects sevoflurane consumption largely, that Biro's equation, because Dion's equation takes into account the sum of products of each segment anesthesia and minimal changes in components, such as the vaporizer dial concentration in percent, FGF and duration which the concentration was set up. The sevoflurane consumption was significantly (p<0,05) lower under MFA with FGF=400 ml/min, compared with LFA with FGF=500 ml/min and 700 ml/ min. When applying the MFA greater influence on sevoflurane consumption has the fresh gas flow than the vaporizer dial concentration, whereas with an increase of FGF to 500?700 ml/min greater influence on consumption has anesthetic vaporizer dial concentration than FGF. The MFA with FGF=400 ml/ min has significantly less the cost of anesthesia, than the LFA with 500?700 ml/min.