ANESTHESIA IN THE BOVINE F. D. Horney* ATARACTIC DRUGS (TRANQUILIZERS) REGIONAL ANESTHESIA THESE PREPARATIONS, usually phenothia- Techniques for regional anesthesia have zine derivatives, are effective in reducing been devised for most areas of the bovine apprehension in nervous animals and pro- body. The most useful are the epidural, vide a means of producing a state of paravertebral, cornual, regional eye blocks, indifference in the animal during which and regional limb blocks. non-painful, thorough examinations and manipulations can be conducted. The seda- Epidural Anesthesia tive effect of these agents usually is con- This regional block is the one most sistent. Side effects, such as antipyretic, frequently used. The agents most com- hypothermic and hypotensive action will monly used are procaine hydrochloride vary with the specific agent. and lignocaine hydrochloride. The strength Tranquilizers are useful for producing of anesthetic solution used is 2% (1.5- sedation prior to performing surgery under 2.5%). The volume has more bearing on local or regional anesthesia. They may the effect produced than does the strength also be used for premedication in general of solution, although complications have anesthesia, but in some cases they prolong been observed with higher concentrations recovery time. (16, 22). The size of the neural canal and The dosage used depends on the pre- the patency of the intervertebral foramina paration and its route of administration. will influence the effect produced by a In nervous cattle the intramuscular route given amount of anesthetic solution. In is preferred and should precede the ad- rare cases, where repeated epidural injec- ministration of the local anesthetic by 30 tions have been made, there may be diffi- to 60 minutes. The excitation caused by culty in obtaining satisfactory anesthesia. an intravenous injection may nullify the The effect which is produced is used sedative effect of the tranquilizer. to classify the type of anesthesia, and These drugs should be administered within limits consistent results can be according to the prescribed dosage, but achieved with a predetermined amount of the following "thumb rules" may be useful: anesthetic solution. Where motor control promazine and chlorpromazine are usually of the hind limbs is not affected, the block given at the rate of 30 mg. per 100 lb. is referred to as a posterior epidural. (45.5 kg.) of body weight, and acepro- Where there is loss of motor control to the mazine at 7.5 mg. per 100 lb. (45.5 kg.) hind limbs, the anesthetic is called an of body weight. An increase of 100% in anterior epidural. dosage with acepromazine does not cause As variations in response occur, it is untoward effects; however, increased advisable to leave the needle in the epi- dosages may cause the animal to lie down. dural space and to give the anesthetic to This is undesirable for operations which effect over a period of five to ten minutes. are performed better when the animal Posterior epidural anesthesia would be remains standing. even more valuable if it could be main- Tranquilization is most beneficial prior tained for extended periods (20). To to restraint; by using an ataractic, opera- achieve prolonged analgesia a continuous tions such as laparotomy, claw amputa- infusion technique (3) or preparations tion, urethrotomy, and extirpation of containing alcohol may be used (7, 26). interdigital fibromata may be carried out These may, however, cause complications. if the surgical site is aiesthetized. The use of anterior epidural anesthesia is restricted to major surgical procedures, 'Ontario Veterinary College, University of and the possibility of damage resulting Guelph, Guelph, Ontario. during the period of motor incoordination ,24 CAN. VET. JOUR., vol. 7, no. 10, October, 1966 BOVINE ANESTHESIA must be considered. Although it is unusual, excellent analgesia in dairy cows because marked hypotension and respiratory de- of the ease with which landmarks for the pression may occur. Large amounts of sites of injection can be located. In beef anesthetic administered rapidly may cause cattle more difficulty may arise because convulsions. This is usually transient, and of fat deposits obscuring these landmarks. it is thought to be the result of excessive The extremities of four of the lumbar pressure on the dura. The size of the transverse processes usually can be readily animal will govern the effect produced identified (L2,3,4 and 5). In thin cows the and dosages of 20 to 150 ml. may be re- transverse process of L1 can also be felt, quired to produce the desired plane of but L6 in all animals is obscured by the analgesia. Various obstetrical and surgical ilium. Perpendicular lines from the an- procedures may be carried out under an- terior aspect of the extremities of L3, L2, terior epidural anesthesia. The repair of and L1 (Figures 1 and 2) will cross over an umbilical hernia is an example of the the nerve trunks L2, L1 and T13 about 2" kind of procedure which can be performed from the midline. Since most operations in with anterior epidural and local infiltra- the flank region involve incisions in the tion anesthesia. mid paralumbar fossa these three nerves must be anesthetized. If more anterior or Paravertebral Anesthesia posterior incisions are required T12 and In regional anesthesia of the flank, L3nerves may have to be anesthetized. paravertebral nerve blocks are of value in providing anesthesia of the sensory Technique nerves. The use of a regional block, as A small amount of anesthetic solution opposed to local infiltration of the pro- is injected beneath the skin with a 25- posed site of incision or a field block in gauge, one-quarter-inch needle. The skin the form of an inverted "L", eliminates is punctured through the bleb thus formed the necessitv of subsequent injections into with a 16-gauge, two-inch needle. This the muscles as they are exposed. The needle is withdrawn, taking care to de- peritoneum is also anesthetized by the press the skin on either side to prevent air paravertebral block. accumulating under the skin. A four-inch, No difficulty is encountered in obtaining 18-gauge needle is passed through the FIGURE 1. Last thoracic and lumbar distribution to the flank. (Photograph courtesy of Dr. 0. W. Sack.) 225 CANADIAN VETERINARY JOURNAL gesia. A rapid acting anesthetic to decrease this interval has been suggested (15). Peterson Eye Block (23) The incidence of traumatic injuries and neoplastic lesions of the eye and associated structures is relatively low. When they do occur, however, economy usually dictates that the treatment of choice in severe cases will be removal of the eye. Complete analgesia is, unfortunately, not always obtained. The technique requires a curved needle to by-pass the coronoid process of FIGURE 2. External palpable landmarks for the mandible. The hypodermic needle paravertebral anesthesia. (four and one-half inches), is inserted in the angle formed by the zygomatic and skin puncture and the lumbodorsal fascia. supraorbital processes, which is just below The anesthetic solution should be injected and slightly posterior to the lateral canthus as the needle progresses in order to block of the eye (Figure 3). The concavity of the dorsal branches and to eliminate the the needle should face posteriorly (Figure tendency of the animal to arch its back, 4), and the direction of insertion is slightly as this may shear the shaft of the needle. downward from a horizontal plane. The Most of the anesthetic solution (10 ml.) curve of the needle directs it around the is deposited just below the level of the transverse process by "walking" the needle off the posterior edge and penetrating the intertransverse ligament. The udder and teats may also be anesthetized by blocking the appropriate lumbar nerves (L2, 3 and 4) and the perineal nerve (18); however, this is usually not required since most surgery in this region is confined to the teats which are best blocked by local infiltration at the base of the teat. Other approaches to obtain comparable analgesia have been suggested. These include injec- tions at the extremities of the 1st, 2nd and 4th transverse processes (4), or the FIGURE 3. Arrow pointing to the angle use of a lumbar epidural (1). The lumbar formed by the zygomatic and supraorbital epidural technique is difficult and poten- processes. tially more dangerous than the other techniques. Cornual Nerve Block The site of this regional block is mid- way between the eye and the horn. As the nerve approaches the horn, however, it becomes more superficial and the block may be easier to perform by injecting closer to the horn. The anesthetic solution should be deposited just under the margin of the frontal crest. Analgesia is good in most cases, although in excessively fat animals the nerve may be displaced and more anesthetic will be required. As with other regional blocks, it is necessary to FIGURE 4. Insertion of needle with the wait for at least ten minutes for full anal- concavity of curve facing posteriorly. 226 BOVINE ANESTHESIA anterior edge of the coronoid process and duce fewer side effects, and reduce the the needle is advanced until it strikes the danger of local damage (19). The use of perpendicular part of the palatine bone in tranquilizers, in most cases, will relax the the vicinity of the orbito-rotundum fora- penis so that exposure may be obtained. men (Figure 5). A second injection is Once exposed, local infiltration will pro- required to anesthetize the auriculo- vide sufficient analgesia for the removal palpebral branch of the facial nerve. This of fibromata or severing fibrous bands. is made over the zygomatic arch at the base of the ear. These injections should Regional Anesthesia of the Limbs paralyze all sensory and motor nerves to This type of block is commonly em- the eye and associated structures.