Rat anesthesia monitoring
Working with a professional veterinary anesthesiologist is mandatory! However you still remain responsible for frequent monitoring of anesthesia and assuring the animal’s wellbeing. If your animal no longer appears fully anesthetized, stop working until you are convinced that the animal is fully anesthetized once more.
Always ensure you use sufficient analgesic along with your anesthetic! Before making the first incision into the skin, assure yourself of the depth of anesthesia. Using a surgical forceps, grasp one of the palms of the rat's forelimbs and raise it gently. Hold the animal’s hand, but do not immobilize it. With your other hand palpate the triceps muscle. Pinch the palm firmly with the forceps to induce pain. If you can perceive an activation of the triceps muscle, the anesthesia is insufficient and supplementary doses will have to be given promptly. If there is no muscle contraction, check again at least every 30 minutes. If the triceps does not contract but you suspect it to be somewhat hypertonic, the risk of the anesthesia wearing off is increased and you have to perform the test more frequently.
The same Test can be performed on the animal’s hind limbs by grasping a foot and palpating the Hamstring muscles.
Rat anesthesia monitoring – pitfalls, tips and tricks
When performing the test be careful not to immobilize the animal’s hand. Fully stretching out the arm, or fixing it in space will cause the test to be insensitive.
Performing the test without palpating the muscle would be far less sensitive, since the contraction may be too weak to induce visible movement over a joint.
Please note that this test may not work if high doses of muscle relaxant are used.
If you are using intramuscular injections, do not test anesthesia on the limb you are injecting, otherwise the test will become insensitive.
Also consider that when working on the abdominal aorta or femoral vessels, blood flow distal to the vascular clamps is obstructed. In this case, additional injections need to be given in regions with uncompromised circulation before the first vascular clamp is placed.
Documenting the administered dosage in a timetable will help you notice when you have not given anesthesia in a long time.
Rat anesthesia monitoring - basic airway management
If you should notice adventitious respiratory sounds, such as wheezes, you should enter the animal’s upper airway with a large rubber catheter on a 20 ml syringe and extract exudates by suctioning.