The end-tidal desflurane concentration for maintaining bispectral index below 50 in adult patients.

Yokoyama R., Satsumae T., Tanaka M.
Department of Anaesthesiology, University of Tsukuba, Tsukuba, Japan.

Background and Goal of Study: Bispectral index (BIS) target below 50 is considered to be appropriate for unconsciousness during general anaesthesia in adult patients. Minimum alveolar concentration for maintaining BIS below 50 (MACBIS50) of sevoflurane has been reported to be 0.97% in adult patients and to decrease with advancing age [1]. Desflurane has rapid onset and offset, and is widely used for general anaesthesia, preferably in obese and elderly patients. Thus, we evaluated the MACBIS50 of desflurane in different age groups. We hypothesised that MACBIS50 of desflurane decreases with advancing age in adult patients.
Materials and Methods: Sixty patients, American Society of Anesthesiologists physical status I and II, aged 10 to 66 years, who were scheduled for elective surgery under general anaesthesia, were enrolled in the study. They were divided into 10-19 year-old, 20-39 year-old, and 40-69 year-old groups. Anaesthesia was induced with 5% sevoflurane in 6 l.min-1 oxygen by using the incremental increase technique via a face mask. After obtaining muscle relaxation using rocuronium 0.7 mg.kg-1, i-gel was inserted. Then, the volatile anaesthetic agent was changed from sevoflurane to desflurane. The end-tidal desflurane concentration was maintained at 4.0% for 10 min to allow equilibration with cerebral anaesthetic partial pressure followed by a 1 min assessment of BIS taken at 10-sec intervals. BIS data were obtained from an average of 6 BIS values in 1 min, and recorded. The end-tidal desflurane concentration at which BIS was measured was predetermined by the up-down method (with 0.2% as a step size). MACBIS50 was determined using Dixon’s up-down method.
Results and Discussion: MACBIS50 of desflurane was calculated to be 4.17%, 3.53%, 3.33% in the 10-19 year-old, 20-39 year-old, and 40-69 year-old group, respectively. MACBIS50 of desflurane decreases with advance in age (P = 0.007), which is similar to sevoflurane. We were able to examine MACBIS50 more accurately using the protocol that had small step size of desflurane and excluded drugs that could affect BIS value.
Conclusion: These results indicate that we can maintain BIS below 50 with less end-tidal desflurane concentration with aging.
Reference: 1. Br J Anaesth 2009; 102: 331-5.