The safest devices for providing heat to anesthetized animals are circulating hot water blankets or instant heat devices. Because of the high airflow, the risk of hypothermia is heightened when using downdraft tables, chemical fume hoods, or biosafety cabinets. Animals should be provided with a heat source during the pre-operative, intra-operative, and postoperative periods. The most frequent complication of small animal anesthesia is hypothermia resulting in prolonged recovery or death of the animal. Monitoring instruments must be properly calibrated, as inaccurate information may be misleading and could result in a compromised condition or fatalities. Pulse oximetry, capnography, and electrocardiograms can be used in larger rodents to monitor pulse, oxygenation, and heart rate. Core body temperature can be monitored in rodents, including mice. ![]() Various types of instrumentation can assist in monitoring the anesthetized patient. Respiratory pattern and frequency is also easily monitored and will give an indication of anesthetic depth and other potential complications. The color should be a bright pink to red and not dusky gray or blue. This will give an indication of tissue perfusion and oxygenation. Monitoring should include inspection of the mucous membranes and exposed tissues. Any reaction from the animal indicates that the animal is too light and that additional anesthetic should be given. Once the anesthetic has been given time to take effect, the anesthetic plane can be assessed by pinching the toes, tail or ear of the animal. Do not allow them to get too light or too deep. To avoid contamination of the lubricant, do not touch the tip of the tube to the skin or eye surface.Īnesthetized animals must be monitored during the procedure to assure that they stay in the proper anesthetic plane. Anesthetized animals should have their corneas protected with an ophthalmic lubricant. ![]() Some anesthetics, such as ketamine, abolish the blink reflex. If using injectable anesthetics, it is important to weigh each animal and dose each according to its body weight. Controlled substances (pentobarbital, ketamine) require additional record keeping. Injectable anesthetics are widely used in rodent surgeries (e.g., ketamine/xylazine mixtures, pentobarbital, tribromoethanol). Depending on the size of the canister and the manufacturer’s recommendations, the canister should also be weighed during especially long procedures to assure its continued effectiveness. Charcoal canisters must be weighed before, and after, each use and must be replaced after an increase in the recommended weight. A charcoal canister ( Figure 1.12.6) attached to the part of the breathing circuit for expired gases can also be used for scavenging. Placing the chamber in a chemical fume hood ( Figure 1.12.4) or a type IIB biosafety cabinet ( Figure 1.12.5) that is vented to the outside are other methods than can be used to scavenge waste anesthetic gases. Do not use induction chambers taller than this for induction of anesthesia. Downdraft tables are usually only effective up to a height of 6–8 inches from the surface. This will cause a loss in its ability to effectively scavenge gases. It is important not to completely cover the surface of the downdraft table. One acceptable method of scavenging is the use of a downdraft table ( Figure 1.12.3). When using gas anesthetics you must account for scavenging of waste gases. Inhalant gas anesthetics are administered using precision calibrated vaporizers ( Figure 1.12.2). ![]() Analgesics can be injected, applied topically in a drop-wise fashion to the surgical area and/or supplied in the food or water. Consideration must also be given to the application of pre-, intra-, and post-operative analgesia. Select the anesthetic based on the type of surgical procedure, the length of the surgical procedure, the equipment available and the expertise of those who will be responsible for administering the anesthetic ( Flecknell, 1996 Kohn, 1997 Swindle, 2002). Considerations for Anesthesia and Analgesia, an Introduction (See Unit 1.4)
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