The volatile anesthetic consumption: the evaluation methods and correlation between them

Abstract

AIM: The volatile anesthetic consumption assessment has been done in a prospective study by using the vaporizer weighing method and the Dion’s and Biro’s equations in the endocrine organ tumors patients undergoing surgical invervention in a specialized center. Determine the correlation between evaluation methods.MATERIALS AND METHODS. 180 patients with surgical endocrine diseases were divided into 2 groups: 1st group – the main group (92 patients) – induction with sevoflurane started from FGF = 2000 ml/min, 2nd group – control group (88 patients) – induction with sevoflurane started from FGF ≥ 4000 ml/min. The volatile anesthetic consumption assessment was estimated by using the Biro’s and Dion’s equations and the vaporizer weighing method (VW) and the correlation between the methods also has been assessed. The following end-point were calculated: the total sevofl urane consumption for the anesthesia period, the sevoflurane consumption until the switch-over on the low / minimal gas flow, the time from the sevoflurane induction to the switch-over on the low / minimum gas flow, the mean FGF before and after the switching on the low / minimum gas flow.RESULTS AND DISCUSSION. It was noted that the calculated parameters according to the Biro’s and Dion’s equations were significantly lower (by the Wilcoxon test, p < 0.05) in both groups compared to the VW method. However, there is a direct correlation between the evaluation methods according to the Spearman correlation coefficient (p <0.05). A strong direct correlation relationship of the Dion’s equation was revealed with the parameters of the VW method for both FGF = 2000 ml/ml and FGF ≥ 4000 ml/min. The Biro’ sequation has a strong correlation with the VW method only in the main group. There was no significant difference in concordance with the Wilcoxon test between the groups for the time from the sevoflurane induction to the switch-over on the low/minimum gas flow: the sevoflurane saturation period was 10.40 ± 0.36 min in the main group, 9.80±0.63 min in the control group. However, the sevoflurane consumption during this saturation period was significantly higher (p <0.05 by the Wilcoxon test) in the control group (4.16 ±0.19 ml) vs the main group (2.75 ± 0.07 ml). The specific gravity from the total sevoflurane consumption for this period (according to the Dion’s equation) was 50.0 ± 1.6% in the control group and 40.2 ±1.3% (the significant difference by the Wilcoxon test, p <0.05). The initial sevoflurane concentration on the vaporizer was without significant difference between the main and control groups and it was amounted to 3.25±0.04% and 3.3±0.04%, respectively. While the average sevoflurane vaporizer concentration was significant (p <0.05 by the Wilcoxon test) higher in the main group (2.97 ± 0.03%) compared with the control (2.78 ± 0.05%).CONCLUSIONS. The Biro’s and Dion’s equations allow the volatile anesthetic consumption assessment as well as the vaporizer weighing method. There is a strong correlation between the methods (rs ≥ 0.95, p <0.05). The Dion’s equation reflects the consumption of sevoflurane to a greater extent due to it takes into account the sum of the products of each anesthesia segment and the minimum component changes. The sevoflurane consumption by the Dion’s equation is strongly correlated with the parameters of the vaporizer weighing method for both the initial FGF = 2000 ml/min and FGF ≥ 4000 ml/min. The initial FGF with the sevoflurane induction in 2000 ml/min (the main group) is more effective than induction with FGF ≥ 4000 ml/min. A significantly lower the sevoflurane consumption was observed in the main group both by the vaporizer weighing method and by the Dion’s equation at the same anesthesia duration.