Comparison of the Depth of Anesthesia Produced with Dexmedetomidine- Sevofl urane or Medetomidine-Sevofl urane by Using Bispectral Index Monitoring

Abstract

ABSTRACT Background: Bispectral index (BIS) monitor was developed to utilize the depth of anesthesia by estimating electroencephalogram (EEG) signals. BIS, which is the numerical value of EEG derivative, is used for evaluation of depression of central nervous system (CNS) in human medicine. The depressive effect of sedative and anaesthetic agents on CNS in human is correlated to BIS. Dexmedetomidine (DEX) is administered as continuous infusion during anesthesia and surgery in humans. DEX is a hypnotic with high selectivity for α 2-adrenergic receptors. Materials, Methods & Results: Adult female New Zealand rabbits (mean ± SD body weight 3.8 ± 0.5 kg) were procured from a certifi ed commercial source to use in medical researches. The animal number in each of the two study groups was four, for a total of eight. The rabbits were randomly divided into two equal groups (n = 4). The rabbits DEX group were administered 20 mcg/kg of i.v. DEX HCI for premedication. Medetomidine (MED) group was administered 20 mcg/ kg of iv MED for premedication. Induction was provided by 5% of sevofl urane + 4 L/min oxygen via glove mask in the both groups. General anesthesia was maintained with 3% of sevofl urane + oxygen on spontaneous respiration for 30 min. The animals' temporomandibular region was shaved; its fat was eliminated with ether before the study. Human sensors were used as BIS sensor consisted of 5 electrodes. Three were placed into frontal area as the remaining two into the preauricular area. After ensuring the connection of the sensor to the BIS monitor, BIS value was continuously followed and recorded at 0 min (T0), 1 st (T1), 5 th (T5), 7 th (T7), 9 th (T9), 15 th (T15) 20 th (T20), 25 th (T25) and at 30 th min (T30) in both groups while the rabbits were awake. At T1 measure point, DEX and MED were applied; sedation was produced at T5; 5% of sevofl urane was administered through glove-mask method at T7 for induction; general anesthesia was obtained at T9 and continued during T15, T20, T25 and T30; they were awakened at the end of 30 th min. On the day preceding the study, they were sedated; their femoral arteries were localized and catheterized under local anesthesia following sedation. At T0, T1, T5, T7, T9, T15, T20, T25 and T30 measure time points, the catheter-transducer connection was established for mean arterial blood pressure (MAP) measurement; for ECG monitoring, ECG electrodes were attached to all four extremities of the subjects and, ECG tracings from lead II were monitored and recorded on the multi-channel monitor. The pH was kept between 7.35 -7.45, as PCO2 between 35 -45 mmHg. All animals in both groups were documented during the study for Anesthesia Score (AS). MAP and BIS decline in DEX group at the end of 1st min at statistical signifi cance (P < 0.05). At the same time point, AS was recorded higher in DEX group (P < 0.05). In the comparison of DEX group with MED group at T5; HR, MAP and BIS markedly declined in DEX group (P < 0.05); however, AS was found higher in DEX group as being statistically signifi cant at the same time point (P < 0.05). As it was at T5, Heart Rate (HR), MAP and BIS were also found statistically signifi cantly low in DEX group at T7 and T9; while AS was found higher as compared to MED group (P < 0.05). BIS value in MED group was low at a statistical signifi cance level at T15, T20, T25 and T30 time points (P < 0.05). Discussion: In present study, sevofl urane administration with glove mask method provides suffi cient anesthesia in the rabbits which were premedicated with DEX and MED in experimental studies or surgical procedures during veterinary practice. Besides the vital parameters and AS monitoring, BIS monitoring is also an effective method in determination of the depth of anesthesia in rabbits