Local and Regional Analgesia

Local analgesia is commonly used for procedures such as dehorning, castration, cyst removal, and wound repair. Lidocaine is probably the local analgesic agent most com­monly used for goats in the United States; other agents include 2% procaine, 2% mepivacaine, and 0.25-0.5% bupi- vacaine solutions.

Mixtures of lidocaine and bupivacaine are used to pro­vide immediate analgesia and prolonged duration of pain relief, though meat and milk withdrawals have not been established for bupivacaine. Lidocaine (1 mg/kg) and bupi­vacaine (0.5 mg/kg) can be mixed in the same syringe for over 12 hours of analgesia when used for digital nerve blocks (Clarke et al. 2014). An estimated maximum dose for bupivacaine is 2 mg/kg, but it has a lower margin of safety than lidocaine (Clarke et al. 2014).

Lidocaine

Lidocaine (formally known as lignocaine in the British and Australian markets) has a historical reputation of being toxic to goats. This can be easily demonstrated if small kids are injected without consideration of the total drug dosage being administered per unit bodyweight. In most species the convulsive threshold dose of lidocaine hydrochloride is 10 mg/kg intramuscularly (IM) (Gray and McDonell 1986a), and it appears to be approximately 9 mg/kg IV in goat kids (Venkatachalam et al. 2018). These authors observed no toxicity with an IV dose of 7 mg/kg. For a kid that weighs 3 kg, a 10 mg/kg dose would be equivalent to 1.5 mL of 2% lidocaine. In general, a dosage of 5-7 mg/kg should be safe. Dilution of the lidocaine to 1% or even 0.75% with saline permits use of a larger vol­ume of analgesic before the toxic level is approached. This is especially helpful if the local blocks (a total of four injec­tions) are to be used when disbudding newborn kids or a line block is used for a large abdominal incision.

Drowsiness, nystagmus, and convulsions are early signs of lidocaine toxicosis (Covino and Vassallo 1976; Venkatachalam et al. 2018). Hypotension, respiratory arrest, and circulatory arrest occur at about five to six times the convulsive dose (Gray and McDonell 1986a). Goats suf­fering from slight overdoses recover spontaneously, whereas severely affected animals should receive oxygen therapy (if available) and 0.5 mg/kg diazepam IV or a short­acting barbiturate to control convulsions. When PCO₂ is increased, the convulsive threshold is lowered (Covino and Vassallo 1976). Another treatment for local anesthetic tox­icity is intralipid emulsion therapy. The dosing protocol is extrapolated from small animal medicine, but the use of this therapy for Pieris poisoning has been reported in goats (Bischoff et al. 2014). Resolution of clinical signs can serve as an endpoint, or the treatment can be repeated, so long as serial blood sampling does not indicate development of lipemia.

In human medicine, and more recently in veterinary medicine, lidocaine has been buffered with sodium bicar­bonate to reduce pain associated with intradermal or sub- dermal injection. A mixture of commercial 2% lidocaine is diluted 5 : 1 or 10 : 1 with 8.4% sodium bicarbonate. The resulting solution has a more physiologic pH (7.3 rather than the 6.0 of the straight lidocaine), but the exact mecha­nism of pain relief is not known (Palmon et al. 1998). Lidocaine with epinephrine is more acidic, with a pH of about 4 (Frank and Lalonde 2012), and thus buffering is even more important with this preparation. No trials have been published concerning efficacy of buffered lidocaine for controlling injection pain in goats.

Paravertebral Block

A line block or an inverted L-block 2-3 cm cranial and dor­sal to the proposed incision site provides good analgesia for celiotomies.

Alternative injection sites, closer to the midline (proxi­mal paravertebral), have also been described (Gray and McDonell 1986a; Hodgkinson and Dawson 2007; Valverde and Sinclair 2015). In an adult dairy goat, the transverse processes of L1 and L3 are located and a point marked over the center of each approximately 3 cm from the midline. A small subcutaneous (SC) bleb of analgesic may be placed at these two spots. Then a 20-gauge, 6 cm spinal needle or a 20-gauge, 3.8 cm needle is introduced through the skin at the point over L1, directed straight down onto the trans­verse process, and walked off the anterior edge of the bone. When the needle pops through the intertransverse liga­ment, aspiration is performed to assure no venous injec­tion, and 3-5 mL of 1% lidocaine or a lidocaine-bupivacaine mixture is deposited just ventral to the ligament. The nee­dle is then withdrawn slightly and an additional 2 mL deposited above the ligament to block the dorsal branch of the nerve. Next, either repeat off the anterior aspect of L2, or else the needle is walked off the caudal aspect of the transverse process of L1, where 5 mL is deposited below and 2 mL above the intertransverse ligament.

Intravenous RegionalAnalgesia

The distal limb of a goat can be anesthetized easily by injecting a local anesthetic into a superficial vein of the limb distal to a tourniquet (Babalola and Oke 1983). This is most desirable when treating serious wounds of the extremity or when amputating a digit. The tourniquet (such as an Esmarch rubber bandage) is applied above the elbow or hock to raise the cephalic vein (crosses the ante­rior aspect of the middle third of the forearm) or the recur­rent tarsal vein (in front of the gastrocnemius tendon laterally). A volume of 3-4 mL of 2% lidocaine solution delivered IV distal to the tourniquet has been recom­mended for Pygmy goats; 5-7 mL is appropriate for larger goats (Gray and McDonell 1986a). For a distal lesion, the tourniquet may be applied in the midmetacarpal or mid­metatarsal region, a superficial vein located, and a smaller volume of analgesic injected IV if this is deemed desirable. The likelihood of hematoma formation can be reduced by using a fine-gauge needle and applying pressure (as with a bandage) over the injection site post injection. Analgesia is complete within 10 minutes and lasts until the tourniquet is removed. To avoid potential lidocaine toxicosis, do not remove the tourniquet for at least 15-20 minutes after the injection (Taylor 1991). The tourniquet should remain on the limb for no longer than 45 or 50 minutes to avoid post- surgical or delayed ligamentous and neuropathic pain, though it has been claimed that no long-lasting adverse effects are observed after application for two hours (Clarke et al. 2014).

Caudal Epidural Block

The most cranial movable joint of the tail is usually between the first and second caudal vertebrae.

A longer duration of local anesthesia and a block that extends forward to provide adequate anesthesia after 40-50 minutes for flank laparotomy or cesarean section can be achieved by adding xylazine at 0.07 mg/kg to the lido­caine (Scott 2000). Although this technique was originally developed for sheep, it also appears to work for goats. Mild ataxia may develop and persist for several hours. Analgesia of perineal tissues appears to last for more than 24 hours. Numerous other drugs have been used for longer-duration epidural analgesia in small animals (Otero and Campoy 2013), and dosages could be cautiously extrapo­lated for use in goats.

Sacrocaudal extradural anesthesia for an even longer duration has been described in sheep. An injection of 2 mL of 48% ethyl alcohol in sheep averaging 64 kg created anesthesia of the genital area, croup, and thigh that per­sisted for one to two weeks, but did not impair mobility. A 0.80 ? 40 mm needle is directed cranioventrally until it touches the bony floor of the vertebral canal between the last sacral and first (movable) caudal vertebrae.

Anterior Epidural Anesthesia

Mammary gland surgery, vasectomy, laparotomy, embryo transfer, prolapse repair, and treatment of hindlimb frac­tures are among the procedures that may be performed under spinal anesthesia. The anterior epidural block is performed at the lumbosacral junction, using a 1.5-3 in. 20-gauge spinal needle with stylet. The site is a palpable depression caudal to the dorsal spinous lumbar processes and between the tuber coxae; it should be clipped widely and the skin prepared as for surgery. If the animal is restrained in lateral recumbency with the lumbosacral spine flexed, the opening between vertebrae at the lum­bosacral junction is effectively larger. In sternal recum­bency, hindlimbs should be extended and directed cranially. The skin may be desensitized with 1-2 mL of local anes­thetic and an initial skin puncture made with a large-bore needle. The finer spinal needle is then directed straight into the space between vertebrae. Many practitioners may also use a Tuohy needle, which is designed for epidural injection. The tip is blunt, to reduce the chance of iatro­genic trauma or inadvertent subarachnoid injection. The tip of the needle is also curved, making the bevel direc­tional. The operator points the bevel cranially, allowing the injectate to be delivered cranially.

Appearance of spinal fluid at the hub of the needle when the stylet is removed usually occurs if the subarachnoid space has been entered. For epidural injections, care should be taken that neither blood nor spinal fluid can be aspi­rated before delivering the injectate. Approximately 1 mL of anesthetic, such as a 2% lidocaine or 2% mepivacaine solution, is injected slowly into the subarachnoid space for each 10 kg of bodyweight. The dose can vary depending on location of interest (0.1 mL/kg total volume for caudal sur­geries and up to 0.25 mL/kg total volume for abdominal surgeries).

Loss of sensation to the rear limbs is delayed (5-10 min­utes) if the anesthetic is placed epidurally (Riese 1987). Some authors prefer to always give the injection in the epidural location, as there is less risk of respiratory arrest. A typical volume is 1 mL of warmed 2% lidocaine solution with epinephrine/5 kg bodyweight (Nelson et al. 1979; Gray and McDonell 1986a; Clarke et al. 2014). After epi­dural injection, the animal is rolled immediately onto its back if bilateral diffusion of the anesthetic is desired, or maintained in lateral recumbency with the side to be desensitized undermost for unilateral analgesia. Paralysis lasts approximately 3 hours, at least in animals that have been sedated with xylazine (0.1 mg/kg IM). Recovery is delayed (often longer than 11 hours) when 0.75% bupiv- acaine is used for epidural anesthesia (Trim 1989). Linzell (1964) recommends performing an epidural injection while the goat is standing and using a lumbar epidural block (5 mL of 1.5% lidocaine plus epinephrine between L1 and L2) to anesthetize the abdominal wall without paralyz­ing the limbs. Adjusting the concentration of local anes­thetic can allow for analgesia without full loss of motor function to the hindlimbs. For instance, 0.125% bupiv- acaine dilution will allow for analgesia, and the animal may have full motor capabilities post procedure. If the pro­cedure is short, mild ataxia may occur. Various additives (Otero and Campoy 2013), including opioids and alpha-2 agonists, may also be used to potentiate analgesia without increasing local anesthetic concentration.

Extradural anesthesia using xylazine at 0.07 mg/kg diluted in sterile water to a volume of 2.5 mL provides adequate anesthesia for a flank incision for cesarean sec­tion of ewes 40-50 minutes later, whether the xylazine is given at the lumbosacral or the previously discussed sac- rocaudal site (Scott and Gessert 1997). Medetomidine (0.020 mg/kg in 5 mL of sterile water) administered epi­durally at the lumbosacral site provides adequate anes­thesia for flank surgery of goats within 5-10 minutes (Mpanduji et al. 2000), although the observed effect may actually represent systemic absorption. Analgesia extends forward to the thorax, front limbs, and neck. IV atipame - zole at 0.08 mg/kg rapidly reverses the analgesia and the cardiopulmonary depression effects induced by the medetomidine (Mpanduji et al. 2001). Lumbosacral epi­dural xylazine at 0.025 mg/kg combined with ketamine at 2.5 mg/kg has been used to produce surgical anesthesia of the perineal region of normal and uremic goats (Singh et al. 2007).

Lumbosacral subarachnoid administration of xylazine at 0.05 mg/kg and of medetomidine at 0.01 mg/kg have been used to provide flank, hindlimb, and perineal anesthesia in goats (Kinjavdekar et al. 2000). Doses of 0.001-0.002 mg/kg medetomidine may be adequate. Use of subarachnoid ket­amine at 3 mg/kg and of subarachnoid xylazine at 0.1 mg/ kg has also been reported (DeRossi et al. 2003). A combina­tion of ketamine at 2.5 mg/kg and either xylazine at 0.05 mg/kg or medetomidine at 10 gg/kg produced com­plete analgesia of the hindquarters for 45-60 minutes in goats (Kinjavdekar et al. 2007).

Sacral ParavertebralAlcohol Block

Long-term (four to six weeks) control of straining associ­ated with rectal or vaginal prolapses can be achieved by injecting isopropyl alcohol (70%) where the sacral nerves exit from the spinal column (Eness 1987; Valverde and Sinclair 2015). A caudal epidural injection of lidocaine simplifies the procedure. A right-handed person inserts the left index finger into the rectum to locate the small bony indentations that mark the junction between two vertebrae. Six injections of 0.25-0.5 mL each are made. The first injections are made bilaterally at sacral spinal nerve S5, directly lateral to the sacrococcygeal junction. An 18-gauge 1-1.5 in. needle is directed down, about 1 cm from the midline, until the point of the needle can barely be felt with the finger positioned in the rectum. The proce­dure is repeated at S4 and S3 bilaterally. The S3 injections are omitted for males because prolapse of the prepuce might otherwise occur. Note that Valverde and Sinclair (2015) claim that the goat only has four sacral vertebrae, but five is actually the norm (see Chapter 1). If the goat has a problem requiring culling, it should be adequately identified; otherwise complete recovery from the current prolapse will tempt the owner to forget predispositions for a repeat prolapse.