Premedication with fentanyl-midazolam improves sevoflurane anesthesia for surgical intervention in laboratory mice

Abstract

Balanced anesthesia allows for a reduced dosage of each component, while inducing general anesthesia of sufficient depth with potentially fewer side effects. Here, we compare two anesthetic protocols combining sevoflurane anesthesia with pre-medication (ketamine [K] or fentanyl-midazolam [FM]) to a sevoflurane monoanesthesia (S) concerning their ability to provide reliable anesthesia suitable for moderate surgery in laboratory mice. Twenty-one female C57BL/6J mice assigned randomly to one of three protocols underwent a 50-min anesthesia and a sham embryo transfer. Heart rate and core body temperature were continuously recorded by telemetry intra-operatively and for three days pre- and three days post-surgery. Intra-operative respiratory rate was determined by counting thorax movements. Body weight, food, and water intake were measured daily for three days pre- and three days post-surgery. The heart rate in the KS group remained at baseline level throughout the 50-min of anesthesia and surgery. FMS caused a lower heart rate and S alone caused a higher heart rate compared to baseline values. Intra-operative body temperature was at baseline levels in all groups. A decreased respiratory rate was observed in all groups compared to baseline values obtained from resting mice of the same strain, sex and age-distribution. Surgical stimuli induced no significant changes in heart rate and respiratory rate in the KS or FMS group but significant respiratory alteration in the S group compared to baseline values obtained 10 s before applying the stimulus. Post-operative heart rate was above baseline values in all groups; with a significant deviation in the S group. There were no changes in body weight, food, and water intake. In summary, FMS was superior to KS and S for moderate surgery in laboratory mice resulting in less inter-individual variability in response to painful stimuli. Fentanyl and midazolam reduced the depressant effect of sevoflurane on the respiratory rate and the negative post-anesthetic effects on the heart rate. Impact statement With approximately 65 million animals used per year mice are still the most prevalent laboratory mammal species worldwide. In course of biomedical research projects approximately 40% of mice will undergo one or more short or long-term anesthesia. Sufficient anesthetic depth, cardiovascular stability, adequate analgesia, and short recovery times are essential requirements of anesthetic protocols to meet animal welfare. Anesthesia in mice and rats are only to be performed by personnel with appropriate basic training and experience. However, more and more adapted and advanced anesthetic protocols, required to answer very specific scientific questions, often exceed the skills acquired through basic training and present a major challenge to researchers. It is therefore of great importance to further develop and evaluate safe and reliable anesthetic protocols as presented in this study to provide new perspectives on this challenging problem.

Mouse Anesthesia: The Art and Science

“…The most commonly utilized inhalant is isoflurane, although sevoflurane has also been used successfully. 24 , 38 , 39 , 42 There are several benefits to using inhalant anesthetics:…”

“… 55 Researchers from the University of Zurich have tested sevoflurane as an inhalant anesthetic for mice, reporting MAC values of 3.25% and finding that surgery can safely be performed using 4.9% sevoflurane. 42 , 72 …”

“… 69 Using sevoflurane, fentanyl-midazolam significantly decreased MAC, and, surprisingly, ketamine had no significant effect on MAC for sevoflurane. 42 , 74 When all of the drugs were tested with an adjusted decreased amount of inhalant, each resulted in a higher RR of the anesthetized mice in direct response to the decreased inhalant concentration required. An additional advantage of using medications before induction is that they can decrease the stress of a tank induction for the animals, although this must be balanced against the stress of handling for the premedication given.…”

Retrospective review of anesthetic and analgesic regimens used in animal research proposals

“…Another advantage of using sedatives and analgesics as pre-anesthetic medication is that this produces a balanced anesthesia where the dosage of each component can be reduced, while inducing general anesthesia of sufficient depth with fewer side effects. For example, administration with midazolam and fentanyl has been shown to improve sevoflurane anesthesia for moderately painful surgeries in mice (Lipiski et al, 2017). Depressant effects of sevoflurane on the respiratory rate and the negative post-anesthetic effects on heart rate were decreased by use of pre-anesthetic medication.…”

Drug class effects on respiratory mechanics in animal models: access and applications

“…The anesthetics can be categorized as inhalational gases and parentally administered agents; the categorization is based on their structure and action mechanisms. [10][11][12][13][14] The existing literature presents certain options for anesthesia in invasive procedures for most studies on respiratory mechanics. Therefore, it is important to analyze different classes of anesthetics and their association with muscle relaxants, opioid analgesics, benzodiazepines, etc.…”