Chapter 15 Misty A. Edmondson Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA Local and regional analgesia are routinely used in cattle because they are considered safe and effective. There are many advantages of local and regional analgesia over general anesthesia. These benefits include the need for minimal equipment (syringes, needles, and anesthetic drug), lower risk of toxic effects especially in debilitated animals, and reduction in the risk of bloat, regurgitation, and nerve or muscle damage that may associated with animals placed in recumbency. Many surgical procedures can be performed safely and humanely using a combination of physical restraint, mild sedation or tranquilization, and local or regional anesthesia. Local anesthetic techniques are usually simple, inexpensive, and provide a reversible loss of sensation to a relatively well-defined area of the body with minimal effects on the rest of the body. The most common techniques used in bovine reproduction include infiltration anesthesia, nerve block anesthesia, and epidural anesthesia. Many local or regional anesthetic drugs are available that can produce reversible loss of autonomic, motor, and sensory function with acceptable onset times and predictable duration.1 These drugs vary in their potency, toxicity, and cost.2 Lidocaine hydrochloride 2% and mepivacaine hydrochloride 2% have become two of the most widely used local anesthetic agents in cattle due to limited toxicity and low cost. Lidocaine hydrochloride has a duration of 90–180 min, is three times more potent that procaine, and diffuses into tissues more widely.1,3 The addition of a vasoconstrictor such as epinephrine (5 µg/mL) to the local anesthetic solution (0.1 mL epinephrine 1 in 1000 added to 20 mL of local anesthetic) increases the potency and duration of activity of both regional and epidural anesthesia. However, local anesthetics containing epinephrine 1 in 200 000 should not be used in wound edges or in the subarachnoid space due to the risk of causing tissue necrosis and spinal cord ischemia.1 Anesthesia of the paralumbar fossa and abdominal wall can be achieved by several techniques, including infusion of the incision or line block, the inverted L block, the proximal paravertebral nerve block, and the distal paravertebral nerve block. These anesthetic techniques are commonly used for reproductive procedures such as cesarean section, ovariectomy, and cervicopexy. Infusion of local anesthetic into the incision site or a line block may be used to desensitize a selected area of the paralumbar fossa. An 18-gauge 3.8-cm needle is used to infuse multiple small injections of 10 mL of local anesthetic solution subcutaneously and into the deep muscle layers and peritoneum. Pain of successive injections may be alleviated by placing the edge of the needle into the edge of the previously desensitized area at an angle of approximately 20–30°.2 In heavily muscled or overweight cattle, it may be necessary to use an 18-gauge 7.5-cm needle to penetrate through the large amount of subcutaneous fat to reach the deep muscle layers. The amount of local anesthetic needed to acquire adequate anesthesia depends on the size of the area to be desensitized. Adult cattle weighing 450 kg can safely tolerate 250 mL of a 2% lidocaine hydrochloride solution.2 Delayed healing of the incision site is a possible complication of infiltration of local anesthetic at the surgical site. The inverted L block is a nonspecific regional block that locally blocks the tissue bordering the caudal aspect of the thirteenth rib and the ventral aspect of the transverse processes of the lumbar vertebrae.4 An 18-gauge 3.8-cm needle is used to inject up to a total of 100 mL of local anesthetic solution in multiple small injection sites into the tissues bordering the dorsocaudal aspect of the thirteenth rib and ventrolateral aspect of the transverse processes of the lumbar vertebrae (Figure 15.1). This creates an area of anesthesia under the inverted L block. Advantages of the inverted L block are that it is simple to perform, does not interfere with ambulation, and deposition of anesthetic away from the incision site minimizes incisional edema and hematoma.1 Disadvantages include incomplete analgesia and muscle relaxation of the deeper layers of the abdominal wall (particularly in obese animals), possible toxicity after larger doses of anesthetic, and increased cost because of larger doses of local anesthetic.1 Figure 15.1 Inverted L. With permission from Lumb and Jones’ Veterinary Anesthesia. The proximal paravertebral nerve block desensitizes the dorsal and ventral nerve roots of the last thoracic (T13) and first and second lumbar (L1 and L2) spinal nerves as they emerge from the intervertebral foramina. To facilitate proper needle placement of anesthetic, the skin at the cranial edges of the transverse processes of L1, L2, and L3, and at a point 2.5–5 cm off the dorsal midline can be desensitized by injecting 2–3 mL of local anesthetic using an 18-gauge 2.5-cm needle. A 14-gauge 2.5-cm needle is used as a cannula or guide needle to minimize skin resistance during insertion of an 18-gauge 10- to 15-cm spinal needle. Approximately 5 mL of local anesthetic may be placed through the cannula to anesthetize the needle tract for further needle placement. To desensitize T13, the cannula needle is placed through the skin at the anterior edge of the transverse process of L1 at approximately 4–5 cm lateral to the dorsal midline. The 18-gauge 10- to 15-cm spinal needle is passed ventrally until it contacts the transverse process of L1. The needle is then walked off the cranial edge of the transverse process of L1 and advanced approximately 1 cm to pass slightly ventral to the process and into the intertransverse ligament. A total of 6–8 mL of local anesthetic is injected with little resistance to desensitize the ventral branch of T13. The needle is then withdrawn 1–2.5 cm above the fascia or just dorsal to the transverse process and 6–8 mL of local anesthetic is infused to desensitize the dorsal branch of the nerve. To desensitize L1 and L2, the needle is inserted just caudal to the transverse processes of L1 and L2. The needle is walked off the caudal edges of the transverse processes of L1 and L2, at a depth similar to the injection site for T13, and advanced approximately 1 cm to pass slightly ventral to the process and into the intertransverse ligament. A total of 6–8 mL of local anesthetic is injected with little resistance to desensitize the ventral branches of the nerves. The needle is then withdrawn 1–2.5 cm above the fascia or just dorsal to the transverse processes and 6–8 mL of local anesthetic is infused to desensitize the dorsal branch of the nerves (Figure 15.2). Figure 15.2 Proximal paravertebral. With permission from Skarda R. Techniques of local analgesia in ruminants and swine. Vet Clin North Am Food Anim Pract 1986;2:631.
Local and Regional Anesthesia for Urogenital Surgery
Introduction
Local anesthetics
Anesthesia for laparotomy
Line block
Inverted L
Proximal paravertebral
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