In September, PRIM&R hosted the webinar Mouse Anesthesia for IACUCs and Researchers, presented by Dr. Jim Marx, DVM, PhD, DACLAM, a veterinarian and researchers whose own research focuses on improving the care of mice in biomedical research. This basic-level webinar, ideal for researchers and IACUC staff, explains the fundamentals of administering and monitoring anesthesia in mice, including how to determine the proper anesthetic depth for a given protocol, how to make basic recommendations about anesthetic protocols to achieve the different planes of anesthesia, and how to understand the basics of anesthetic monitoring as an indicator of correct administration of anesthesia.

After the webinar, Dr. Marx responded to the attendee questions time didn’t permit us to address live. We’re pleased to share those responses with the readers of Ampersand.

We have recently started using carprofen cups and the mfg specifies that the cups can be used for up to five pups. When we added it to our protocol, our recommendation was to separate all animals so there was one cup per cage with one animal. Do you have any experience with these cups and multiple mice?
Jim Marx (JM): I don’t have any personal experience with the cups, but separating the animals makes good sense as a method of ensuring that each animal is getting the analgesic. As a field, we like to give analgesics, and other meds, in the food and water, both out of convenience and as a way of decreasing the stress for the animals. The problem is if they don’t eat or drink the medicated source, the pain will be uncontrolled, which will decrease their desire to eat, further decreasing the lack of analgesic and allowing pain to worsen…forming a vicious cycle. It may be difficult to confirm that each animal is truly consuming the food, but at least when individually housed, we have a fighting chance.

There was a recent publication promoting the use of alfaxalone. Do you have any experience with this?
JM: The alfaxalone, in our hands, works well for imaging procedures, but has a very high mortality when used with laparotomies, probably because of increased absorption of the alfaxalone/xylazine combination when the peritoneum becomes stimulated by the surgery. It worked well on an orthopedic procedure, but monitoring and being ready with atipamezole to reverse the xylazine is important.

What anesthetic equipment do you recommend labs purchase and how expensive is this equipment?
JM: This is a tough question and will really depend on the individual lab. ECG monitors which can be accurate in the 500-700 beats per minute range can be several thousand dollars and up. Many pulse oximeters also aren’t accurate in that range, although they may be able to give good oxygenation information (in white mice, check with the manufacturer/test the mice if using C57BL/6 mice because of the pigment). Monitoring temperature is very important and not too expensive; a couple hundred dollars is probably adequate to get a mouse-appropriate rectal thermometer/thermocouple. Ultimately, you can go a long way by monitoring the reflexes and respiratory rate and effort, if you can interrupt doing the surgery and monitoring these things.

Is sevoflurane comparable to isoflurane?
JM: The referenced article below reports that both can effectively be used in mice, which is consistent with other species. There are some publications showing differences in specific models, so it would be a good idea to check in terms of specific models to see if differences have been demonstrated.

Cesarovic N, Nicholls F, Rettich A, Kronen P, Hässig M, Jirkof P, Arras M. (2010). Isoflurane and sevoflurane provide equally effective anaesthesia in laboratory mice. Lab Animal, 44, 329-36. doi: doi:10.1258/la.2010.009085

How much of an effect does buprenorphine have on anesthetic requirements of isoflurane?
Buprenorphine does decrease MAC for the inhalants. We have seen about a 20% decrease in MAC of isoflurane following buprenorphine administration. Individual monitoring can help monitor the depth of the anesthetized mice, but if your monitoring is limited, then decreasing the isoflurane by a small amount may well increase the safety for the animal without increasing the risk of consciousness under anesthesia. I’ve had problems with buprenorphine if administered immediately after discontinuing isoflurane anesthesia with respiratory depression and apnea. I typically wait to give buprenorphine post-op until the animal can stand and is a bit more alert, provided I have some other analgesic on board protecting the animal during the transition period.

PRIM&R thanks Dr. Marx for sharing his expertise!

The recording of this webinar is available for individuals to purchase in PRIM&R’s online store. If you would like to purchase the webinar for group viewing, please download the order form (PDF) and send it to registration@primr.org.