Having recently discussed general anesthesia we will today cover local anesthesia.
General anesthesia is useful for procedures that are invasive, painful and require total immobilization of the patient. Some procedures, however, just don’t justify completely putting a pet “to sleep.” Instead, one of several local anesthetics can be used to prevent the dog or cat from feeling pain, yet still accomplish the task.
Local anesthesia, sometimes shortened to just “local,” or “LA” is usually administered by injection into or near the site to be operated. A common example of its use is removal of small growths. The injection is usually made directly under the growth. Small masses may then be removed by a biopsy punch, which functions much like a coring device. Excisions can also be made by laser, electrosurgery or scalpel.
Systemic sedation may be added to calm the patient and to minimize movement. Sedation, unlike general anesthesia, does not make a pet unconscious. Some sedatives also have pain-relieving properties, although additional pain medications may also be administered.
Another use of local anesthesia is in a nerve block. Yes, there is a reason our anatomy professors had us learn the whereabouts of all of those body parts. By knowing the exact location of the nerves of the body, veterinarians can administer a local around the specific nerve that serves a certain section of the body and numb that entire area. This is the same technique dentists use when they inject inside our mouths; the location of the injection is specific for the part of the mouth to be worked on.
Spinal anesthesia also involves the use of local anesthetics. Epidural is another term meaning the same thing. Broken down, the term begins with the Latin prefix “epi,” which means upon, followed by “dura,” which is short for dura mater, the outer lining of the spinal cord. The dura mater is imbued with many pain-sensitive nerve endings, and the local is absorbed beyond it to block sensation to the part of the body served by the area of the cord that has been anesthetized.
Local anesthetic medications come in a variety of forms. Their effect varies mainly in duration. Some act very quickly but lose their effectiveness quickly. Others last longer, but take longer to begin to act. A combination of these is commonly used in invasive procedures for what is called a “splash block.” A splash block can be administered by spray device or squirted through a small-gauge injection needle just before closing a surgical incision, such as a spay surgery. By combining fast and slow-acting, short and long duration LAs, pain control begins before the pet awakens from general anesthesia, and lasts for hours thereafter. In combination with injectable and/or oral pain medications, discomfort is alleviated.
Locals can also include epinephrine, a medication that limits blood flow to an area and thus prevents the body from removing and metabolizing the anesthetic as quickly. As less blood circulates through an area, less anesthetic is removed, effectively lengthening the duration. Further time control may be obtained by choosing a short or long-acting local anesthetic.
When it comes to anesthesia, no one technique fits every scenario. Sometimes a combination of techniques is best, which has the added benefit of using less of each medication.