Use of Isoflurane in Rodent Surgery

Presented by:

Dr. Cristina Weiner, Veterinarian

Agenda

Explore the keys to a successful rodent surgery. This webinar will highlight the use of volatile gas anesthetics, specifically isoflurane. You will learn the benefits of using isoflurane as well as supportive care techniques for use pre- and post-operatively that enhance the surgery experience for the rodent.

More about Dr. Cristina Weiner

Dr. Cristina Weiner is a veterinarian that manages Taconic's Surgical Operations with emphasis on training regimens and developing the highest-quality animal models. After graduating with an A.B. degree in the History of Science from Harvard University, she received her V.MD from the University of Pennsylvania. Dr. Weiner was residency-trained in Comparative Medicine at Colorado State University where she also received her M.S. degree in Microbiology.

Download the presentation slides.

Webinar Questions and Answers

Q: What are routine acclimation and recovery times for some classical surgical procedures like laparotomy, catheters placement, etc.?
A: This often depends on the procedure. Taconic recommends at least 24 hours acclimation time and recovery prior to shipment for most surgeries. For "major" procedures (ie those that enter a major body cavity), this recommendation can be extended for up to 72 hours or longer, depending on the procedure.

Q: Do you always need oxygen or can you just use fresh air (containing oxygen) to mix with IsoF?
A: Taconic uses oxygen that can be delivered, regulated, and adjusted via the flowmeter.

Q: What are the justifications for NOT using buprenorphine in surgery?
A: This depends on the experiment and assays being evaluated. Opioids can have adverse effects on the animal, depending on the animal's health status, strain, etc. as well as dose of drug given. An example is gastrointestinal stasis. Also, assays that the investigator is using may also be complicated by opioids. It really depends on the project.

Q: I did not understand the porphyrin staining bit.
A: Porphyrin is a substance secreted normally in rodents by the harderian gland. Normal behavior allows for rodents to groom this away, and so it is less likely that an observer will notice porphyrin in a healthy and normally-behaving animal. However, in animals that are feeling uncomfortable or distressed, observers may notice an accumulation of porphyrin pigment at the eyes, nostrils, or haircoat because the animal's normal grooming behavior changes. This may be an indication, particularly in post-operative surgically-modified animals, that the animal is distressed or potentially in pain.

Q: What do you recommend if you see your animal entering too deep a phase of anesthesia during surgery?
A: Decrease the concentration of isoflurane delivery (or turn it off altogether) but keep your oxygen flow on. Pending appropriate cardiovascular and respiratory function, the delivery of oxygen should help the animal to remove drug from the respiratory circuit. Because the metabolism of iso is rapid, you should begin to notice clinical changes in your animal's anesthetic plane. Constant observation and assessments are critical at this stage in order to be able to respond and intervene further if necessary. Anesthesia records are a great way to keep track of this and prevent the animal from becoming too deeply anesthetized. Anesthesia records afford the opportunity to monitor parameters like HR, RR, body temp, time anesthetized, etc. that help to track the anesthetic experience and prevent negative events.

Q: What are your thoughts about pain medication in food?
A: This really depends on the project and monitoring. It can be very difficult to monitor how much an animal receives (dosage, frequency, etc.) when drug is delivered in food or water. So, there is the possibility that the animal receives not enough or too much. It is also important to be sure of the stability of the drug in either food or water and that it does not degrade (ie. half-life, light-sensitivity, etc). Often administering drugs into food or water may change the pallatability, thereby also changing the animal's food or water intake. The most direct delivery of drug is by direct administration. Considerations for this would be stress to an animal that is not acclimated to handling or dosing. One option - at least for the first dose of drug - would be to deliver drug at the time of surgery or immediately post-op when the animal is still anesthetized.

Q: In your experience, when inducing with iso in a chamber, what's best, placing the animal in an empty chamber or one that's been pre-charged with iso?
A: I prefer to use a chamber that is first void of all gases. Then I turn oxygen on to pre-oxygenate the animal and then the isoflurane.

Q: Are there any particular monitors you use that are designed for rodents or you could recommend?
A: There are a number of commercially-available monitors specifically designed for rodents. A quick internet search for what you are looking for specifically should lead you to them.

Q: Would you use isoflurane for resection of a primary tumor, from subcutaneous xenograft mouse model?
A: This really depends on what you'll be evaluating, the clinical status of the animal, and the size/location of the tumor. If the animal is considered to be a viable anesthetic candidate, then isoflurane is likely an appropriate choice. There is likely to be very rapid induction and recovery from the drug, which is a benefit for the animal.

Q: What dose do you recommend for Buprenorphine in rats?
A: We routinely use buprenorphine in rats.

Q: What body temp is considered hypothermic in rats?
A: Normal body temperature of rodents depends on other physiologic factors and strains; some references list it at 35.9-37.5°C; others at 38-39°C. An accurate way to assess this parameter in your animals would be to monitor normal animals and develop your own range. When considering heat loss in rodents, it is important to know that rodents respond to heat loss by non-shivering thermogenesis. They are particularly sensitive to changes in ambient temperature and water loss and can have a difficult time recovering without appropriate support. It is important to maintain the body temperature as close to normal range as possible during the surgery process.