Anesthetics and sedatives can be divided into several broad categories depending on how they function.
Local anesthesia provides pain control for a specific location on the body. Examples include an epidural before surgery on a rear limb, or a nerve block before a tooth extraction. The local anesthetic prevents the pain impulse from being 'read' by the brain. With animals, local anesthetics may provide pain control, but may not be sufficient to keep the animal still during the procedure. In these cases, a sedative or general anesthetic is typically needed in conjunction with a local anesthetic. For certain procedures, local anesthetics may be used in an effort to decrease the amount of general anesthetic needed and speed up recovery time.
Lidocaine is an example of a local anesthetic. It lasts about 1-2 hours. Lidocaine should be used with caution in animals with certain heart conditions or liver disease. It is used with caution in cats, since cats tend to be more sensitive to it than dogs. Bupivacaine is similar to lidocaine and lasts for 2-6 hours. Morphine may be combined with a local anesthetic for epidurals.
Sedatives and tranquilizers
Sedatives and tranquilizers are used to relax an animal for procedures such as trimming nails, taking x-rays, or drawing blood. These medications are injected either into a muscle or directly into a vein. Sedatives and tranquilizers are commonly used in combinations as preanesthetics before general anesthesia to relax and sedate the animal.
Diazepam (Valium) and midazolam are tranquilizers that are used to relax animals before surgery. They should not be used in pregnant animals, since they could cause birth defects. Acepromazine is another tranquilizer used as a preanesthetic. It should not be used in animals that have seizures, since it may increase the risk of the animal having a seizure. It may also cause hypotension (low blood pressure). Tranquilizers do not provide analgesia (pain relief).
With any of these medications, the animal may be groggy for the remainder of the day, but should be able to stand and walk before he is allowed to go home.
Sedative - analgesics
Some sedatives also provide analgesia (pain relief). Among these are several short-acting drugs, which have reversal agents that quickly bring an animal back to an alert state. An example is Domitor (medetomidine hydrochloride), which is used as a sedative and analgesic in dogs. It is used for minor procedures that do not require muscle relaxation such as the removal of porcupine quills. The medication is given IV (intravenous) or IM (intramuscular), and the animal is allowed to quietly rest for 5-10 minutes while the drug takes effect. Twitching is a common side effect. Once the procedure is done, the animal is given atipamezole hydrochloride (Antisedan) to reverse Domitor's effects. It is given IM and the animal is awake in 5-10 minutes. The pet may have an abrupt reversal of the sedation and become startled. A quiet, darkened area would be the ideal setting for allowing the animal to rest during the reversal process.
General anesthetics are used when an animal needs to be unconscious and unaware of what is being done for an extended period of time, such as for surgery. General anesthetics block the pain sensation, prevent movement during surgery, and usually cause muscle relaxation.
Thiopental is an ultrashort-acting barbiturate, which is used for induction of general anesthesia or for very short procedures, such as suturing a small wound or removing porcupine quills. It is injected directly into the vein and unconsciousness occurs within a minute. Greyhounds and other sight hounds may have a longer recovery period than other breeds. This may be due to their low body fat levels or differences in how the body breaks down the anesthetic.
Ketamine and Telazol are other injectable anesthetics used for restraint or short procedures, such as draining an abscess. Telazol is used in cats and dogs. Ketamine is used in cats; it provides no muscle relaxation. Ketamine and Telazol function differently than most other injectable anesthetics. They produce 'dissociative' anesthesia, which means the animal is not aware of what is going on. The animal's eyes remain open and reflexes are generally present.
When using a general gas anesthetic, the animal is given an induction agent such as thiopental to bring him to unconsciousness. Then the gas anesthetic is mixed with oxygen in the anesthesia machine and is administered via a face mask or an endotracheal tube placed in the pet's trachea (windpipe). Commonly used general gas anesthetics include, isoflurane and halothane. They are both rapidly taken up and eliminated from the body by the lungs. Isoflurane has become the anesthetic of choice in veterinary medicine, and its use is especially indicated for pregnant animals (including c-sections) and for animals with heart problems.
These are a few of the medications available to veterinarians for use during restraint, minor procedures, and general anesthesia. Sometimes the medications are used alone while other times they are used in combinations. Each animal receives the type and amount of medication best suited for his individual needs.