Q&A Report: Simple Tips to Significantly Improve Rodent Surgical Outcomes

Marcel Perret-Gentil, DVM, MS, answers questions from a recent webinar on simple-to-implement techniques to significantly improve surgical outcomes, positively impacting your animal’s recovery and data.

The answers to these questions have been provided by:

Marcel Perret-Gentil, DVM, MS
University Veterinarian & Director
Laboratory Animal Resources Center
The University of Texas at San Antonio (UTSA)

Do you recommend mixing isoflurane with pure oxygen (O2) or room air, or there are no differences?

Pure O2 unless it is a very short procedure. Anesthetized animals can become hypoxic soon after induction of anesthesia so providing room air, which is 21% O2 at sea level, can lead to hypoxia.

What temperature should you warm fluids to, ideally?

Body temperature, about 37-38 degrees Celsius.

Should you Press'n Seal® or cling wrap all of your knobs, etc. once you have sterile gloves on? And should you change this for every animal?

That would be ideal to minimize possible contamination from one animal to another.

Is there a concern of animals overheating when using Press'n Seal® with heating pads?

It is possible to overheat the animals when using a heat pad and more so when using Press’n Seal®, which insulates the animal. However, if you (and should) monitor the animal’s temperature, you should be able to maintain the animal normothermic.

Is there much of a difference if you supplement with fluids before or after the surgical procedure, and how much?

Since anesthetics depress vital centers including blood pressure, the idea is to administer fluids, 10-20 ml/kg, before the start of the surgical procedure. If the procedure is too long and/or you’ve had a significant amount of blood loss, you could consider a second dose of fluids post-op.

Would you recommend fluids for surgery that lasts less than 15/20 minutes?

It is always a good idea to administer fluids pre-op unless the anesthetic episode is very short. It is up to you. If I conduct a procedure that lasts 15 minutes, I provide fluids because although the surgical procedure only lasts 15 minutes, the anesthetic episode is longer.

If using the Press'n Seal®, how do you make sure it is sterile? Do you recommend using UV light on the seal or autoclaving it before use?

No need to sterilize Press’n Seal® since we’ve proven it comes sterile. UV light has low penetration and could only sterilize superficial layers. Press’n Seal® is not autoclavable as it is a weak plastic. Please look at the publications cited in the webinar.

Is there a correlation with better outcomes and the type of anesthetic used (inhalant versus injection)?

Yes. Inhalants (compared to injectables) lead to better outcomes because you have better control of the depth of anesthesia, they are minimally metabolized by the liver (mostly breathed in and out), and induction and recovery is faster. In general, these inhalants lead to decreased morbidity and mortality when compared to injectables.

Do you use made-for-purpose facemasks for rodent oxygen supplementation or other improvised items?

I’ve used both, explained this during the webinar. I like the low profile masks from Kent Scientific, https://www.kentscientific.com/products/low-profile-anesthesia-masks-for-somnosuite/.

Working in a germ-free facility, are there autoclavable enrichment foods available?

Yes, there are. For example, the red huts I showed in the webinar are fully autoclavable. Bio-Serv has a lot of autoclavable enrichment items, https://www.bio-serv.com/category/Rodent_Enrichment_Devices.html

If you are a solo surgeon, how frequently do to stop to check the vital signs during surgery?

Depends on the invasiveness of the procedure. Very invasive procedures require more frequent monitoring. We typically check every 5-10 minutes.

For oxygen supplementation, are you recommending 100% oxygen? What are your thoughts on moderate hyperoxemia (e.g., FiO2 of 35%; PaO2 ~150mmHg) versus severe hyperoxemia (FiO2 or 100%; PaO2 >500mmHg)?

In the human OR, the anesthesiologist typically uses less than 100% oxygen due to the toxicity of pure oxygen. According to my discussions with Dr. Cholowat Pacharinsak from Stanford School of Medicine, he has not seen this toxicity when using 100% O2 in mice and rats for anesthetic episodes that last less than 4 or 5 hours. Oxygen concentrators might be best for longer procedures as the delivered O2 is not 100%.

Do you have any tips specific to working on neonatal mice?

In general, neonates are more prone to hypothermia and close attention to this should be given. Morbidity and mortality tend to be higher in these animals, especially with injectable anesthesia. Supplementation with glucose is very helpful in newborns as they develop hypoglycemia quite fast. To avoid pup rejection, before returning them to their mother, be sure to rub some of the mom’s cage wet bedding on the pups so mom can recognize their scent upon return.

Which is the best way to warm fluids?

Depends on the container. If it is a soft or hard plastic container you can use a microwave, or a steam bath is useful. Sometimes we place the bag of fluids on a heating blanket for 30-60 minutes.

Does the duration of a surgical procedure affect the amount of hydration required?

Most definitely. A procedure that lasts 45 minutes will expose organs to dehydration and fluid loss more than if you were to do a short procedure.

Is it suitable to use Press'n Seal® to wrap the entire animal to keep it sterile?

Yes, it is and in fact I recommend it for these procedures. Place a sheet of Press’n Seal® on the table, sticky side up, then place the animal on its dorsum on the seal, and lastly, place a new sheet of seal on the animal’s ventrum but this time with the sticky side down.

Is maintaining asepsis as important in non-survival surgeries?

It depends. If you are doing non-survival of a relatively short duration, asepsis may not be an issue. At UTSA we have a protocol where pigs undergo terminal surgery but are kept alive for 48-72 hours. In such cases, aseptic technique is a must because the infection from lack of asepsis will affect the entire animal and results.

What is the type/brand of supplement you feed post-op mice?

I recommend ClearH2O’s gel cups, https://www.clearh2o.com/shop/animal-research-products/nutrition-products/. You can consider 76A, Boost and Recovery.

Does Kent Scientific's equipment work on small non-human primates (NHP)?

The anesthesia system works on animals up to 1000 grams. You can reach out to their sales team for more information: https://www.kentscientific.com/contact/general-support/.

Do you need to use specific antiseptics or local antibiotic after skin surgery after suturing?

It is up to you. If you think that contamination of the closed wound is an issue you could consider triple antibiotics, Neosporin, or bacitracin ointment. Keep in mind that some rodents don’t like these ointments on them and will clean the area if they can reach it and that may create wound problems.

How to identify hyperthermia?

When the temperature of the animal is >3 degrees above normal, i.e. 40 Celsius and above.

For the nesting material, is it better to use a soft one or hard one?

Soft is better.

Is ketamine/xylazine cocktail good as an anesthetic agent or not? What are other best alternative drugs to use as an injectable anesthetic?

It is neither good nor bad. Each anesthetic has its place in research. There are times when ketamine/xylazine are the drugs of choice but for most procedures, inhalant anesthetics such as isoflurane and sevoflurane are superior for the following reasons: inhalants (compared to injectables) lead to better outcomes because you have better control of the depth of anesthesia, they are minimally metabolized by the liver (mostly breathed in and breathed out), and induction and recovery is faster. In general, these inhalants lead to decreased morbidity and mortality when compared to injectables.