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17 Regional Anesthesia for Urogenital Procedures
Darcie R. Sidelinger
Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Starkville, MS, USA
Introduction
When performing urogenital surgery in cattle, local and regional anesthesia are routinely utilized. They are a safe and effective alternative to general anesthesia in the large animal patient. Some benefits to using local and regional anesthesia include the need for minimal supplies to administer the necessary medications (anesthetic of choice, needles, and syringes), decreased risk of toxic effects, and minimizing bloat, regurgitation, and temporary or permanent nerve or muscle damage associated with positioning animals in recumbency. Many of the urogenital surgeries can be performed safely, rapidly, and humanely using physical restraint, sedation, and local or regional anesthesia. These techniques are easy to perform, the drug cost is minimal, and the effects are temporary and fairly well localized to the site of administration. This eliminates the widespread effects of general anesthesia on the entire body. The most common techniques used in bovine reproduction include infiltration anesthesia, nerve block anesthesia, and epidural anesthesia (Table 17.1).
Table 17.1 Common nerve blocks with landmarks and volume of lidocaine for reference.
| Nerve block | Landmark(s) | Volume of lidocaine |
|---|---|---|
| Proximal paravertebral | T13, L1, L2 | 6–8 ml ventral and dorsal to the transverse processes |
| Distal paravertebral | L1, L2, L4 | 10 ml dorsal and ventral to the transverse processes |
| Caudal epidural | S5–Co1, Co1–Co2 | 0.5 ml /45 kg |
| High‐volume caudal epidural | S5–Co1, Co1–Co2 | 1 ml/5 kg |
| Sacral paravertebral | S3, S4, S5 | 2–3 ml per foramina |
| Internal pudendal | Lesser sacrosciatic foramen | 20–75 ml per side |
| Castration | Skin and testicle | 5–10 ml subcutaneous; 10–15 ml/200 kg into testicle |
Local Anesthetics
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 minutes, is three times more potent than procaine, and diffuses into tissues more widely [1, 3]. Mepivacaine has a duration of 120–180 minutes, which is longer than lidocaine; however, the time to onset of anesthesia is similar. Although, bupivacaine has an even longer duration of action (up to 360 minutes), it is not recommended for routine use in cattle due to risk of inadvertent intravenous administration which could lead to toxic effects [4].
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 for Laparotomy
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.
Line Block
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 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.
Inverted L
The inverted L block is a non‐specific 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 [5]. 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 17.1). This creates an area of anesthesia under the inverted L block. Advantages of the inverted L block are that it is simple to perform, it 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].