Comparison of bispectral index and vital parameters in rabbits receiving propofol or isoflurane anesthesia

ABSTRACT

Background: Reflexes, muscle tonus, heart rate, respiratory frequency and blood pressure are parameters that can be used to evaluate the depth of anesthesia. Bispectral index (BIS) was developed with the objective of evaluating quantitatively the sedative and hypnotic effects of anesthetic drugs. It is widely used to assess central nervous system depression levels. The objective of this study was to compare changes in BIS and several vital parameters during general anesthesia achieved with either propofol or isoflurane, following premedication with dexmedetomidine. Materials, Methods & Results: Adult female New Zealand rabbits (Mean ± SD body weight 3.6 ± 0.4 kg) were procured from a commercial source certified for medical experimentation. The animal number in each of the two study groups was four, for a total of eight. The animals were checked before the study to ascertain their good health. The animals, randomly allocated to either of two study groups, were given dexmedetomidine, 20 µg/kg i.v. Induction was realized by means of propofol, 8 mg/kg i.v. in the propofol group (n = 4), and by administration through a glove mask of isoflurane, 4%, in the isoflurane group (n = 4). Anesthesia maintenance was assured by propofol, 0.6 mg/kg/min or 2% isoflurane with oxygen, respectively. Both anesthetic applications were well tolerated by the rabbits. Before premedication (T0), at the time points of 1 (T1) and 5 min (T2) after dexmedetomidine injection, 1 min into anesthesia induction (T3), and 10 (T4), 30 (T5) and 60 min (T6) after start of maintenance, the following were recorded BIS, systolic, diastolic and mean arterial blood pressure, heart rate and Anesthesia Score (AS). Blood gas analysis, serum sodium and potassium, blood glucose level, hemoglobin and hematocrit were measured at time points T0 and T6. MAP dropped significantly lower in the propofolgroup at times T2, T3 and T4 (P < 0.05). Under BIS monitoring, BIS values were also found to be relatively lower in the propofol group at times T1, T2 and T4, corresponding in this to AS. At T4, the BIS values were, respectively, 69.5 ± 6.24 and 68.25 ± 3.59 in the isoflurane and propofol groups (P < 0.05). In summary, premedication with dexmedetomidine did not, differently than with humans, assure deep sedation; BIS values, in parallel with our AS evaluation, reached levels of deep anesthesia in the maintenance stage both in the propofol and isoflurane groups. BGA results in arterial blood (pH, PaO2, PaCO2, BE, HCO3) as well as hematocrit (Hct), Na+, K+, glucose, hemoglobin (Hb) were recorded and reported in Table 2. A significant increase in pH was noted at T6 (P < 0.05) in the propofol groups compared to animals given isoflurane (7.39 ± 0.01 vs 7.35 ± 0.003, respectively), all measurements remaining within the normal values. Discussion: Vital parameters showed parallelism with the values of both our AS and BIS in this study, in which we administered general anesthesia with either propofol or isoflurane to rabbits premedicated with dexmedetomidine. Publications on humans show that surgical anesthesia is realized at BIS values under 60; BIS fell in rabbits in parallel to MBP at 10, 30 and 60 min of anesthesia, and AS also showed that the depth of anesthesia was adequate. No surgery having been performed in this study, we think that the parameters noted in this paper should be investigated in future studies that include surgery.