Guidelines for the care and use of laboratory animals dictate that rodent survival surgery be performed aseptically and in a humane manner. This is to ensure that there is minimal trauma to the animal; there is no infection due to the surgical procedure itself; to prevent hypothermia; and to decrease the pain and discomfort induced by the invasive steps.
This video will review the general considerations for pre-surgical planning, intraoperative monitoring and post-operative care. This will be followed by demonstration of a few types of surgeries performed in biomedical research today.
First, let's review the preparatory steps that a scientist should perform prior to any rodent surgery. The area where the surgery would be performed should be free of clutter and must be sanitized with an appropriate hard surface disinfectant. Note that the area should not be in direct line with the ventilation, as the drafts could contribute to hypothermia of the patient. To further prevent hypothermia, the surgery platform should be insulated with a supplemental heat source.
The surgical instruments should be sterilized before hand. Wrap them in individually autoclavable pouches and place them in a tented configuration inside the autoclave to allow complete steam penetration. When serial surgeries are performed, sterilize the instruments between each animal with a bead sterilizer for 10-15 seconds. Make sure to cool down the instrument before using it on the next animal.
Several days prior to surgery, observe the animal to evaluate their body condition, appetite, water intake, and urine and feces output. Additionally, note the body posture and the condition of the hair coat. An animal displaying a hunched posture or an unkempt hair coat may be harboring a disease and may not be a good candidate for surgery.
Because rodents have such a high metabolic rate and very limited fat reserves, they should not be fasted prior to surgery. Evaluate the animal's hydration status by performing the skin elasticity test. To do this, gently lift the skin above the shoulders. In a normally hydrated animal, the skin will quickly fall back into place, whereas in a dehydrated animal the skin will not immediately go back to its normal position.
After setting-up the surgery area and making sure that the animal is in good health, you can begin preparing the animal for the procedure. The first step is anesthetization. In order to understand how to induce and maintain anesthesia refer to another video in this collection. After the animal is sedated, remove it from the chamber and place it on the shaving pad. Note that shaving should be performed in an area away from the surgical platform to prevent any contamination. Apply lubricant eye ointment to prevent drying of the eyes, especially for relatively long surgeries.
Shaving is commonly done using electric clippers, preferably with a surgical A40 blade. A standard two-inch blade can be used for rats, whereas a half- to one-inch blade is more appropriate for mice. To avoid nicks and cuts, first stretch the skin to stabilize it. Then place the flat of the blade on the skin and move it against the direction of the hair growth. The shaved surgical field should be sufficiently large to allow for incision and suturing without inclusion of fur into the surgical wound, but as small as possible so as to avoid the exacerbation of hypothermia. Alternatively, hair may be removed using depilatory cream, which dissolves the hair at the follicle. First, apply the product to the surgical site area using a swab. After approximately three minutes, rinse and clean the skin with sterile water to remove all traces of the cream in order to avoid irritation or chemical burns.
Following hair removal, use a moistened gauze sponge to remove any debris including hair and dander. Then, using a gauze pad pre-soaked in antiseptic or cleansing solution, scrub the area starting at the incision site and extending outward in a circular pattern. Next, apply the rinsing liquid in the same circular pattern - spiraling from the incision line to the periphery of the surgical field. Repeat the cleansing and rinsing cycle at least three times. After the final rinse, place a sterile gauze pad - wet with either alcohol or iodine - over the surgical field. The gauze will remain in place while the animal is transported and positioned on the surgical platform.
The next step is to position the animal. For dorsal procedures, place the animal in prone position. Secure the limbs onto the platform using ligature or tape. Care must be taken not to: compromise circulation to the feet, cause excessive tension on the limbs, impair the joints due to over stretching, or impede animal's breathing. Once the animal is prepped and positioned onto the surgical platform, remove the gauze covering the incision area and now animal is ready for draping.
Remember that draping is an aseptic technique, so the surgeon ought to be wearing sterile gloves, a bouffant cap, a surgical mask, and a clean lab coat or a sterile surgical gown. Drapes can be made of cloth, which is reusable, or disposable paper or plastic adhesive material. Drapes of any type should never be shaken or waved to unfold. They should be carefully opened to avoid contact with non-sterile areas, equipment, and personnel. If the drape is not precut, then unfold enough so that you can create an opening using sterile scissors that will be large enough to adequately expose the surgical area, but not so large to allow exposure of unshaved and unprepared body surfaces.
Next, place the drape over the animal keeping the hands on the side of the drape that will not touch the patient. And lastly, adjust it so that the surgical field is visible through the opening. This allows one to maintain a sterile field at the surgical site for the entire procedure. If using a paper drape with an adhesive window, first peel the paper from the adhesive area. Then, unfold the drape carefully, turn it so that the sticky side is facing the animal, and place it over the surgical area. Then gently press the adhesive to the surgical field to create a seal with the skin.
After prepping, the next step is surgery. So let's take a look at a few things that the surgeon should bear in mind during and post surgery. While under anesthesia, animals must be monitored for body temperature, respirations, and heart rate until they are fully recovered.
For direct monitoring of body temperature, a rectal probe designed specifically for rodents must be used. The normal range is 35.3 to 38° C that is 97.5 to 100.4° F. Alternatively, for indirect monitoring, place the thermometer next to or under the animal. Although this will not give an exact body temperature, it can indicate the effectiveness of the heat source and allow adjustment to reduce or increase the heat as needed.
Meanwhile, throughout the procedure visually monitor the heart rate, respirations, and the color of the tail. Occasionally, additional monitoring can be done through the use of electrocardiograms, which evaluates the cardiac status of a rodent during anesthesia and surgery.
Post surgery, the animal should be returned to a recovery cage placed partially over a heating pad and food should be made easily accessible. The partial placement on the heat pad allows the animal to move off of the heat source after it has regained consciousness. In addition, pre-emptive and postoperative analgesia should be provided whenever possible. See Table 1 below for the list of recommended analgesics, their dosage, route and frequency of administration.
Now that you're well versed with the considerations, let's look at some of the survival surgeries performed by biomedical researchers.
In order to manipulate the brain in living animals, scientists often perform stereotaxic surgeries using a specialized equipment called the "stereotaxic frame". Using this tool and a three-dimensional coordinate system, one can target specific locations to measure brain activity, induce lesions, or perform genetic manipulations.
Scientists also perform surgery to create animal models of human disorders. Here, the researchers created a "skin flap" model to study ischemia induced tissue damage. By implanting a metal window in the shaved skin, the investigators were able to visualize the region's microcirculation in a live animal for several days. In another experiment, researches performed surgery to induce bone defect by drilling a plate into a rat's femur, and then studied in vivo bone healing process with the help of X-rays.
You've just watched JoVE's video on considerations that one should bear in mind before, during and after performing rodent surgery. Together, these measures would reduce the probability of infection and hypothermia, and help in ameliorating pain and discomfort to the animal, which will in turn increase the probability of a successful survival surgery. As always, thanks for watching!