Effect of midazolam and butorphanol premedication on inhalant isoflurane anesthesia in mice

Isoflurane is a representative inhalant anesthesia used in laboratory animals. However,isoflurane mediates respiratory depression and adverse clinical reactions duringinduction. In the present study, we established a novel balanced anesthesia method in micethat combined isoflurane anesthesia with midazolam and butorphanol (MB). Thirty-four maleC57BL/6J mice received either isoflurane alone or isoflurane with an intra-peritoneal MBpremedication (3 mg/kg midazolam and 4 mg/kg butorphanol). The minimum alveolarconcentration (MAC) in each group was evaluated. Induction time and adverse clinicalreactions were recorded in each group. Core body temperature, heart rate, respiratoryrate, and oxygen saturation (SPO₂) were assessed before and for 1 h afterinduction. Premedication with MB achieved a significant reduction in MAC compared withisoflurane monoanesthesia (isoflurane, 1.38 ± 0.15%; isoflurane with MB, 0.78 ± 0.10%;P<0.05). Induction time was significantly shortened with MBpremedication, and adverse reactions such as excitement or incontinence were observed lessfrequently. Furthermore, isoflurane anesthesia with MB premedication caused increase ofrespiratory rates compared to isoflurane monoanesthesia. No significant decrease ofSPO₂ was observed in MBI anesthesia, while a decrease in SPO₂ wasapparent with isoflurane monoanesthesia (baseline, 98.3% ± 1.1; 10 min after induction,91.8 ± 6.4%; P<0.05). In conclusion, premedication with MB waseffective for the mitigation of respiratory depression induced by isoflurane in mice, withrapid induction and fewer adverse clinical reactions.