I've adapted a procedure for mice from a collaborator that uses rats for urodynamic studies.
I use 0.5g/mL urethane to anesthetize mice. I start off with 1.2g/kg subcutaneous, and increase the dose as needed with i.p. injections. I keep the mouse's cage on a heating pad until it's immobile, and then put it on a heating pad, also using a heat lamp. I monitor its temperature throughout the procedure.
Once the mouse loses the toe pinch response, I perform a tracheotomy and then close the wound. Then I open the abdomen and insert PE-50 tubing into the bladder. I close that wound and flip the mouse over, with its feet tucked under.
However, when I switched from using 3-month-old mice to 10-month-old mice, the mice would die around the time I get the tubing into the bladder. Usually the mouse would start to gasp for air, and I would observe changes in the heart beat before it would die.
Does anyone have any suggestions on how to perform urodynamic studies on older mice?
Thank you!
I don't have any experience with that, however our institution uses ketamine/xylazene with isofluorane for most surgeries. When gasping is observed it's usually because there is too much isofluorane and the mouse needs more O2. Do you think the tracheotomy might need to me changed for the larger mice so that they can get more air?
Thank you! I'm trying to avoid changing the anesthetic because my collaborator has told me that urethane is the least likely to alter bladder contractions and because urethane is the most commonly used anesthetic for this procedure in the literature. The mice would usually start gasping while they still have a toe pinch response, which is particularly frustrating because they're in respiratory distress while still able to feel pain. Also, the tubing for the tracheotomy usually fits pretty snug, so I don't think the tubing is too small for a mouse trachea. Occasionally the tubing is a little too big for a smaller mouse, in which case I have to pull the tubing to decrease the diameter.