The effects of bispectral index monitoring on end-tidal desflurane concentration and desflurane consumption

Abstract

Aim: The aim of the study is to assess whether the concentration of end-tidal desflurane decreases or not with the use of bispectral index (BIS) monitoring to standard anesthetic practice. Materials and Methods: In all patients anesthesia was induced with thiopental sodium 5 mg kg-1 and fentanyl 1 ?g kg-1. The trachea was intubated using vecuronium 0.1mg kg-1. Anesthesia was maintained with desflurane, in a mixture of nitrous oxide 1 L min-1 and oxygen 1 L min-1. Desflurane with 4-6 % concentration was administered to patients for 5 min after tracheal intubation. Additional fentanyl 1 ?g kg-1 was given before skin insicion and no more was given. The desflurane concentration was then changed as follows: In Group I; if the patients displayed clinical signs consistent with inadequate anesthesia, the inspired desflurane concentration was increased or decreased by 1 %. In Group II, the anesthesiologist adjusted the concentration of desflurane to achieve a target BIS in the range of 50±5. Results: The mean BIS value was 35.98±2.3 and 45.68±5.3 in Group I and II, respectively. BIS levels in Group I were significantly lower during surgery (p=0.001). The end tidal desflurane concentrations in Group I were significantly higher than Group II (Group I: 4.61±0.48, Group II: 3.92±0.61) (p=0.007). The desflurane consumption was total 917.84±14.08 mL and 838.02±11.73 mL in Group I and II, respectively. Conclusion: These findings indicate that the use of BIS, as it decreases the end-tidal concentration of desflurane and desflurane consumption, has become a technique which determines the depth of anesthesia safely.