Talk:Regional analgesia

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LOCAL ANAESTHESIA

local anaesthesia constitutes the use of those substances which have selective, transient, paralytic action on sensory nerve endings. These effects can be achieved by either application of such substances to mucosa, abraded surface or by intradermal sub dermal or sub mucous infiltration.Local anaesthesia may be defines as deliberately induced and temporary loss of sensation in a defined body area without impairment of consciousness. The agents may act either on sensory nerve endings or trunks and temporarily paralyses nerve function. They are directly act on sensory nerve endings or end plates.

Local anaesthetic agents are injected to desensitize the nerve endings. It includes extravascular (e.g. linear infiltration) and intravascular (intravenous regional anaesthesia) administration of local anaesthetic agents. In peripheral nerve blocks, either minor (e.g. digital) or major (e.g. brachial plexus) nerves are blocked. Major nerve blocks are rarely used in ruminants. The central neural blocks include epidural and spinal, the former is commonly used in ruminants.Majority of the routine surgical procedures in cattle can be done using local analgesic techniques. These techniques are simple, safe, economical and do not require sophisticated equipment. Moreover, even old and poor surgical risk patients can withstand local analgesia without major complications.

Uses or indications of local anaeshesia General Use: Diagnostic and therapeutic punctures Incision of Haematoma/Abscess/ Wound drainage Excision of small superficial tumors/Cysts and Foreign bodies Suturing of superficial wounds Castration in male animals. Special Uses: Horse:castration in standing animal ,Trephining sinuses,Tenotomy,Tooth operation,docking Cattle,sheep& Goats: Laporotomy,Caesserian section, digit amputation,Operation of external genitalia,Castration. Pig: castration Dog: Tooth extraction,Ectrpian, Entripion, digit amputation,Tail docking,Castration of male. Cat: Castration.

Advantages of local anaesthesia 1.In large animals necessity of casting is avoided. 2.It is easy to perform. 3.The danger of toxicity is less than general anaesthesia. 4.Assistance and continued control of anaesthesia is avoided. 5.It is useful when patient’s condition permits avoidance of general anaesthesia. 6.Post anaesthetic sequelae are reduced.

Contraindications 1.Infection, Danger of necrosis (deficient circulation, diffusion of local anaesthesia is insufficient. 2.Hypersensitivity to anaesthetic agent. 3.Weak circulatory system is risky(Anterior epidural anaesthesia,blocking of sympathetic system in the posterior part of the body resulting into accumulation of blood and a low blood pressure. 4.In duration

Substances commonly employed

Qualities of an ideal local anaesthetic 1.It should have good penetrating qualities. 2.It should have lower systemic toxicity. 3.It should be water soluble, stable in solution and easily sterilized. 4.It should not produce pain, tissue damage or irritation during or after injection. 5.It should have high potency so that low concentration can be used to give complete anaesthesia. 6.It should have a rapid onset and long duration of action. 7.It should have larger margin of safety and a reversible action. 8.It should be rapidly absorbed from mucosa or mucous membrane. 9.It should be compatible with adrenaline. 10.It should be free from idiosyncratic reaction.

Cocaine: It is no longer in common use as numbers of synthetic compounds have replaced it. Moreover, it is astrong protoplasmic poison and produces toxicity on absorption. It is being mentioned here as a historical fact.

Procaine: Procaine is a white transparent crystalline powder which is freely soluble in water. The solution can be easily sterilized by boiling. The solution with yellowish tint should be discarded. It has prompt and pronounced effect which is intensified by addition of adrenaline. It is much less toxic then cocaine but when goes intravenously, its toxicity approximates to that of cocaine. Excessive intravenous injection of procaine produces convulsions and respiratory failure. Procaine is hydrolysed by liver and blood stream into para – aminobenzoic acid and diethylaminoethanol. It is used for infiltration anaesthesia, 0.5 to 1 % with or without adrenaline is used. In spinal and regional anaesthesia, 2% solution is adequate. The procaine is a poor surface anaesthesia due to its low rapid solubility. The anaesthetic effect begins within 3 to 5 minutes after injection and persists for ½ to 1 hour.

Lidocaine: A white powder of lidocaline is readily soluble in water. The solution is stable when boiled or autoclaved repeatedly. It is more efficient local anaesthetic particularly for perineural and spinal injection. It is 3 times more potent than procaine. The addition of adrenaline increases the duration of anaesthesia. When goes intravenously, the toxicity of lidocaine resembles to that of procaine. Lidocaine tends to diffuse more widely and easily in tissues. For infiltration anaesthesia, 0.5 to 1% solution is used. For epidural and regional anaesthesia, 2% solution of lidocaine with adrenaline (1:50,000) is most suites. It is a good surface anaesthesia and can be used as 2 to 4 % solution with or without adrenaline. The onset of action begins 1 to 2 minutes after injection and persists for 1 to 2 hours.

Tutocaine: It is readily soluble in water and solution withstands boiling for a short period. The aqueous solution of tutocaine hydrochloride is stable. It is considered to be more potent infiltration anaesthesia than procaine. However, it is twice as toxic as procaine. Tutocaine hydrochloride is suitably used for infiltration anaesthesia as 2 to 4 % solution. The toxic properties of tutocaine hydrochloride have discouraged its use in veterinary practice. The action of tutocaine starts within 3 to 5 minutes after injection and persists nearly for 1 to 11/2 hours.

Cinchocaine: The aqueous solution of cinchocaine hydrochloride is stable to heat and is neutral in nature. It is highly potent local anaesthetic and produces anaesthesia of longer duration. However, its toxicity approximates three times to that of cocaine and twenty five times to that of procaine. It is a very effective surface anaesthetic. The optimum concentration for infiltration is 0.5 % and for regional and surface anaesthesia is 1 to 2 %. Decicaine: The aqueous solution of decicaine is stable against boiling and repeated sterilization. Decicaine is 2 to 3 times more toxic than cocaine. It is nearly 10 times more potent surface anaesthesia than procaine and produces anaesthesia of much longer period. A 2% solution of decicaine is useful for mucous membrane. A 0.5 % solution is useful for ophthalmic purpose. Concentration of 1 to 2 % is sufficiently strong for infiltration and spinal anaesthesia. More than 2 % concentration of decicaine produces local inflammation and tissue necrosis. The above said toxicity of decicaine has made its use rare in veterinary practice. The action of decicaine appears 2 to 3 minutes after injection and persists for 1 to 3 hours.

Mepivacaine: This compounds closely resmbles lidocaine hydrochloride and slightly less toxic. It is not commonly used in veterinary practice.

Bupivacaine: The local analgesic effect of bupivacaine is in rate of onset and depth to that of lidocaine and mepivacaine but is of much longer duration. It possesses more or less all the required general properties of a local analgesic drug. Bupivacaine is approximately four times as potent as lidocaine hence 0.5 % solution is equivalent in nerve blocking activity to a 2 % solution of lidocaine. There are very few reports on its use in veterinary practice. However, it is indicated in solutions, where prolonged analgesia is required. Potentiation of Local Anaesthesia By Vasoconstrictor The addition of vasoconstrictor in local anaesthetic solution potentiafes its action and prolongs the duration of anaesthesia. The vasoconstrictors produce vasoconstriction hence the anaesthesia is removed from the site of injection much slowly. There is retarded absorption of local anaesthetic into circulation with slow destruction. This helps in reduction of toxicity and simultaneous increase in duration of anaesthesia. Similarly, use of vasoconstrictor in highly vascular area minimizes blood loss. The use of adrenaline and noradrenaline produces marked vasoconstriction. The optimum concentration of adrenaline is 1:50,000. However, the concentration of adrenaline up to 1:100,000 gives satisfactory result. The use of adrenaline mixed local anaesthetic in extremities like digits, tail and earflap may result into ischaemia and thereby necrosis of the part. The accidental intravenous injection of such solution produces toxic symptoms. The use of vasoconstrictors should, therefore be minimum. Local anaesthetics can produce toxicity. This can be of three types depending upon the symptoms. 1.Local ¾ It is manifested by ischaemia and necrosis at the site of injection. 2.Vascular ¾ It is observed specially in those cases, where dose of anesthesia reaches the toxic level in the circulation. E.g. decreased cardiac output resulting in paleness, slow and feeble pulse rate. 3.Cerebral ¾ It is characterized by excitement nausea and vomition barbiturates. Counter act convulsive action of local anaesthetic. Other treatments are based on the symptoms.

Precautionary measures against toxicity. 1.Minimum necessary does should be used. 2.The total quantity of drug should be limited. 3.Minimum concentration of the drug should be used. 4.Aspiration prior to any injection to avoid vasopuncture is necessary. 5.Addition of vasoconstrictors e.g. adrenaline is adfvantageous to retard absorption or promote slow absorption in vascular areas. Use of suitable premeditation to depress CNS prior to the use of anaesthesia is helpful in reducing the total dose requirement.

VARIETIES OR TYPES OF LOCAL ANAESTHESIA OR METHODS OF PRODUCING LOCAL ANAESTHESIA The commonly used local anaesthetics are protoplasmic poison. These substances have selective affinity for nervous tissue. The addition of vasoconstrictors keep the concentration of these substances at low level and the toxic reaction becomes very less. The local anaesthesia can be given in any one of the following forms.This classification depends on the site at which nerve impulse transmission is interrupted. It is mainly of three types: A. TERMINAL ANAESTHESIA:Local anaesthetic drug acts directly on sensory nerve endings or end plates. It is of five types.

B. REGIONL (NERVE TRUNK) ANAESTHESIA: Loss of conductivity is produced in a nerve trunk. The drug is injected either under nerve sheath or neurelemma (endoneural) or in direct viscinity of nerve (perineural) from where it penetrates the nerve fibres by diffusion.

C. SPINAL ANAESTHESIA: It is a form of nerve trunk anaesthesia. The nerves are blocked either within or at their exit from the vertebral canal. The anaesthetic solution may be introduced into the space occupied by loose connective tissue, fat and venous plexus outside the tough spinal covering of dura mater (extradural or epidural) or into the cerebrospinal fluid filled (Arachnoid) space below the dura mater (Sub-dural).

Terminal: Surface anaesthesia Infiltration anaesthesia Refrigeration anaesthesia Venous or intravenous anaesthesia Regional (nerve Trunk) anaesthesia Spinal anaesthesia: Extradural Subdural

A. TERMINAL ANAESTHESIA: Local anaesthetic drug acts directly on sensory nerve endings or end plates. It is of five types. 1.Surface anaesthesia: is routinely used to desensitize the mucous membranes of the eye, teats, genital system, oral cavity, nasal cavity etc. Use of ice, ethyl chloride and some agents like lignocaine hydrochloride produce topical anaesthesia. Anaesthetic agent is introduced onto a surface capable of absorption The diffusion of local anesthetics after surface application through mucosa, tendon sheath or svnovial membrane paralyses superficial pain receptors.. Ex: conjunvtiva, serous membranes, tendon sheaths, and synovial membranes of joints. This includes intra articular anaesthesia and synovial sheaths besides the freezing of the superficial layer of the skin. Ethyl chloride spray is most commonly used. This vaporizes quickly causing freezing. However, its action is very superficial and transient and can only be used for incision of superficial abscess. This form of anaesthesia is also used for mucous membrane that is in the eye, nose, mouth, vulva, gland penis and urethra. The use of 2% lignocaine or 4% procaine hydrochloride is generally preferred. A piece of cotton wool or gauze soaked in these solutions is placed at the mucous membrane or affected pain for 5 minutes to achieve effective anaesthesia. In the deep cavities, the spraying with solution provides satisfactory anaesthesia.For ophthalmic use, 4% lignocaine is safe. It does not irritate the eye and does not cause dilation of the pupil or vasoconstriction. Drugs used: Ice, ethyl chloride spray, 2% cocaine, 2% lignocaine and 4% procaine EMLA Paste

2.Infiltration anaesthesia: The solution of local anaesthetic is infiltrated in the operative field either by single injection or multiple injections. Thus brining contact between drug and nerve endings. The diffuse infiltration of anaesthesia at the site of operation anaesthetizes the sensory nerve endings. This form of anaesthesia is useful for minor surgical procedures like treatment of wounds, skin incision, and extirpation of superficial tumours. This technique is very useful when used in conjunction with basal narcosis for major operations in the animals with poor surgical risk. After the skin has been disinfected, a fine sharp needle is inserted superficially and the anaesthetic solution is injected to produce a desensitized block. The tissues are then infiltrated layer by layer up to the required depth. During the infiltration of the deeper tissues, the solution should only be injected after aspiration to avoid its entrance into the blood vessels. If blood is aspirated back into syringe, the needle should be withdrawn slightly and reinserted into the tissues in different direction. About 1 ml of solution is required for every centimeter of incision. (i) Linear block: This block is preferred in those areas, where the innervasion is derives mainly from one side. In this procedure the solution is injected first to the subcutaneous tissues from one puncture site and thereafter, the subsequent injections are made by further advancing the needle in the musculature and so on to the full depth of the tissues.

(ii) Field block: The anaesthetic solution is infiltrated around the periphery of an operative area to block all sensory nerve trunks. This is choosen when sensory nerves approach the area from all the directions. It is most commonly used in veterinary practice for rumenotomy and caesarean section. The solutions are injected fanwise in certain planes of the body so as to block all the nerves approaching the operation site. iii. Inverted L block : Combination of two linear infiltration techniques one in vertical and another in horizontal manner in a shape of inverted L. Common during flank operation in cattle. Skin under all the layers of muscle should be infiltrated with local anaesthetic.

(iv) Ring block: It is useful for the extremities. In this block, a transverse plane through the whole extremity is infiltrated with local anaesthesia. The application of tourniquet proximal to the site of injection makes this technique more effective. This block is particularly useful for amputation of digits. i. Ring block: Local anaesthetic solution is infiltraed all around, in a tarnsverse plane, with special attention to large nerve trunks. It is useful techinque to desensitize extremiteis eg. teats and digital region.

v. Cup block : Infiltration of local anaesthetic in a divergent manner below the base of a part ex. teat. vi. Diamiond block : Infiltration of local anaesthetic in a different directions like a pan fashion from the entry of needle. ex. infiltration for tumour. 3.Refrigeration anaesthesia: It causes local anaesthesia when low temperature is induced on cutaneous surface to eliminate nerve function. For refrigeration anaesthesia liquid carbonic gas, ice cube, volatile solvents like methyl bromide, ethyl chloride, ether etc. are used. Ethyl chloride and ether however are inflammable and hence care should be taken not to use them with electro cautery or near fire and other electric installations. 4.Venous anaesthesia (Intra-venous-retrograde anaesthesia) It is seldom used in these days. It is an intravenous injection of local anaesthesic together with a tourniquet applied to the part of body above the site of injection. vii. Intravenous regional analgesia (IVRA) : It is a simple and safe technique to produce regional analgesia of lower limbs, for surgery of the digits. The animal is secured in lateral recumbency with the limb to be anaesthetized in lower most position.

Technique : A tourniquet is firmly applied proximal to the injection site. Inject 10-20 ml of 2% of lignocaine into any superficial vein distal to the tourniquet which becomes prominent due to engorgement. Analgesia below the tourniquet devlops in about 10 minutes and remains as long (maximum 50 minutes) as the tourniquet remains in position. After tourniquet release, sensation and motor functions return within about 10 minutes.

(i). Intra-synovial anaesthesia. The main difficulty in this method is to enter into the articular cavity properly. The synovial fluid of the articular cavity should be drained out and then anaesthetic solution is injected. The joint is massaged and manipulated for through dispersion of the solution in the cavity. Perfect sterilization of the needle and anaesthetic solution is essential. The intra-synovial anaesthesia is useful for the diagnosis of lameness. The anaesthetic solution is injected sub-sunovially and synovial membrane along with articular surfaces is anaesthetized. The amount of anaesthetic solution varies according to the size of the joint. In horses 15 to 20 ml and in dogs 2 to 3 ml is needed. The use of cinchocaine hydrochloride is restricted to mucous membrane. When high concentration of cinchocaine goes into systemic circulation, it produces fall in blood pressure, brandycardia and cardiac arrythmia. A solution of 1:2000 is effective for use on mucous membrane. The addition of adrenaline prevents the possible tissue irritation and hyperaemia due to high concentration of cinchocaine. The onset of action is within 10 minutes, which persists for 4 to 8 hours.

(ii). Distal inter-phalangeal or Pedal (Coffin) joint: The joint is extended before the injection of anaesthesia. A needle (8 to 10 cm) is inserted 1 to 2 cm above the coronary border and 1 to 11/2 from the midline of the hoof. The needle is then directed downwards, medially and backwards. The elevation of the foot facilitates entrance of the needle into the joint.

(iii) Proximal inter-phalangeal or Pastern joint: An imaginary line joining the attachment of medial and collateral ligament to the first phalanx is drawn. Site of injection is the point 1 cm below the line. The needle is introduced near the mid point of this line and is directed obliquely downwards and inwards.

(iv) Fetlock joint: The fetlock joint is entered in the triangular space formed by the third metacarpal bone, the proximal sesamoid bone and the suspensory ligament. The injection is made in the standing position.

(v) Carpal joint: The proximal and the middle carpal joints are used for injection. The injection is given from the dorsal aspect pf flexed joint. The distal joint communicates with the middle one between the third and the fourth carpal bones and thus does not require the injection separately. Both the joint cavities can easily be palpated when the leg is flexed.

(vi) Elbow joint: The elbow joint is entered either in front of the ligament, the needle is inserted under the margin of the lateral condyle of the humerus and injection is then made directly into the joint. If the needle is inserted behind the ligament, the anaesthetic is injected into the communicating bursa under the lateral flexor of the carpus.

(vii) Shoulder joint: The entry to the shoulder joint is best made in the fissure between the anterior and posterior part of the lateral tuberosity of the humerus. The needle is then directed backward and inward in a horizantal plane. The flow of synovial fluid confirms the successful puncture.

(vii) Stifle joint: This joint has three synovial sacs, one for the femoro-patellar articulation and other two medial and lateral in the femoro-tibial articulation. (a) Femoro-patellar articulation:

This joint can be entered on either side of the middle patellar ligament.

(b) Medial sac of the femoro-tibial articulation: The medial sac can be entered between the medial patellar ligament and the medial femoro-tibial ligament behind the medial patellar ligament and above the margin of the tibia. (c) Lateral sac of the femoro-tibial articulation: The lateral sac is preferably entered between the lateral frmoro-tibial ligament and common tendon of the long digital extensor and the peroneus tertius. The needle is inserted above the margin of the lateral condyle of tibia behind the grove occupied by the tendon.

(ix) Hip joint: The needle is introduced in s notch formed between the anterior and posterior parts of the trochanter major. This is most easily performed on the standing horse. A 15 cm long and 2 mm thick needle is used for injection. A small incision is made in the skin at the site of insertion of needle under local infiltration anaesthesia. The needle is then inserted at the right angle to the skin and directed horizontally. Above described techniques of the horse are applicable in cattle and dog also with minor modifications.

B. REGIONL (NERVE TRUNK) ANAESTHESIA: Loss of conductivity is produced in a nerve trunk. The drug is injected either under nerve sheath or neurelemma (endoneural) or in direct viscinity of nerve (perineural) from where it penetrates the nerve fibres by diffusion.

REGIONAL ANAESTHESIA OF HEAD The regional anaesthesia is performed by blocking the sensory nerves or nerves innervating the area of operation and the perineural injection of particular nerve is commonly known as regional anaesthesia. This is an interruption in the conductivity of a nerve trunk and the sensitivity of an operative field is lost without touching it. The uses of regional anaesthesia are therapeutic and diagnostic. The closest possible contact of local anaesthesia with nerve trunk is necessary to achieve perfect regional anaesthesia. The successful perineural anaesthesia requires through knowledge of the topographical anatomy of the particular region and the site of injection.

1. Cornual nerve block : Regional blocks of head in cattle were never popular in veterinarians of our country except cornual which is essentially performed for dehorning.The cornual nerve, a branch of the lacrinal nerve, passes through the periorbital tissue dorsally to run along the lateral border of the frontal crest to the base of the horn. Site and Technique : The block is most easily performed 2 to 3 cm in front of the horn. The nerve is situated just below and 1 to 2 mm inside the margin of frontal crest. After palpating the margin of frontal crest, A 18 G needle is inserted first directly towards the margin of the crest and then underneath it. Cornual artery and vein are suited immediately lateral to it. If these vessels are punctures, the needle should be withdrawn and then redirected medially. Nearly 12 to 15 ml of Lignocaine hydrochloride gives more satisfactory anaesthesia.

2. Retrobulbar nerve block : to desensitize the eye ball proper Site Depression just caudal to the point where the supraorbital process meets the zygomatic arch. Technique : A 12 cm long 18 G needle is introduced aseptically through the skin and pushed till it strikes the coronoid process of the mandible. It is redirected towards the pterygopalatine fossa rostral to the foramen orbitorotandrum at a depth of 8 to 10 cm, and 15 to 20 ml of 2% lignocaine may be injected for effect.

3. Auriculopalpebral nerve block : The nerve is blocked to cause motor paralysis of the eyelids. The site and technique is depositng the local aneasthetic solution superficially under the subcutaneous tissue at the dorsal border of the zygomatic arch in front of the base of the ear in bovines.

4. Mental nerve block : Used for surgery of the lower lip and lower jaw. Site : The mental formane is located on the lateral aspect of the ramus just behind the fourth incisor. The mental nerve is blocked in or near the mental foramen. The mental foramen is situated at then junction of the incisive and molar parts of the lateral body of the mandible. Technique : A 3 to 4 cm long 20 G, slightly bent needle, with its concave side laterally, is inserted slowly into the foramen and 10 to 15 ml of 2% lignocaine is injected. The procedure is repeated on the other side of the face if required for bilateral blockade.

5. Mandibular - alveolar nerve block : The nerve is a branch of the mandibular nerve and supplies the molar teeth. Site : The mandibular foramen at the medial aspect of the ramus of the mandible. The situation of the mandibular foramen is at the point where the line passing along the masticatory surface of the mandicular cheek is crossed by the perpendicular line running through the lateral canthus of the eye.

Technique : The needle is inserted from the angle of the jaw along the medial surface of the ramus of mandible, at a point where an imaginary line along the masticatory surface of the lower molar teeth is crossed by another imaginary vertical line from the lateral canthus of the eye. A 15 cm long, 18 G needle is used. About 20 ml of 2% lignocaine is injected to induce analgesia of the molar teeth, incisors and lower lips.

6.Infraorbital nerve block : is used for surgery of the upper lip, nostrils, incisors and gums. The intraorbital nerve is the continuation of maxillary division of fifth carnial nerve. It is purely sensory and supplies maxillary and alveolar branches which supply the teeth, alveolar peristeum and gums. On emerging through the infraorbital foramen, it supplies sensory branches to nasal region, upper lip, cheek and nostrils. Site : Infraorbital nerve emerges from the infraorbital foramen. Rostral to the facial tuberosity, dorsal to the first molar tooth. The infraorbital nerve is blocked either at (i) its point of emergence through the infraorbital foramen or (ii) within the infraorbital foramen or (iii) within the pterygopalatine fossa and at the point where the nerve enters the maxillary foramen. Technique : A 4 cm long, 20 G needle is inserted about 2.5 cm deep into the canal and 5 to 10 ml of 2% lignocaine is injected to block the nerve. However, the methods (i) and (ii) are easy to perform and give definite results. The infraorbital foramen is situated on a line connecting the medial canthus with the nostrils and 4 to 5 cm dorsorostral (anterior) to the rostral end of the facial crest. It is covered by levator nasolabialis muscle. By pushing this muscle sharp upper margin of the infraorbital foramen is felt. For this injection, 5 cm long 19 gauge needle is useful. By injecting 10 ml of 2 % procaine hydrochloride solution the whole anterior half of the face can be anaesthetized including the cheek teeth up to second molar. When the nerve is blocked within the canal, it is necessary to pass the needle for about 2 to 3 cm in the canal.

7.Supraorbital nerve block: The frontal nerve is a branch of the ophthalmic division of the fifth cranial nerve and passes through the supraorbital foramen as the supraorbital nerve. It supplies sensory branches partially to the skin of forehead and upper eyelid. The frontal nerve of the horse is blocked where it emerges through the supraorbital foramen at the base of the zygomatic process of the frontal bone. A 2.5 cm, long, 19 gauge needles are introduced into the foramen up to a depth of 1.5 to 2 cm and 5 to 7 ml of 2% procaine hydrochloride is injected. (Fig.8)

REGIONAL ANAESTHESIA OF LIMBS: The nerve supply of the digits in cattle is much more complex than horse. Although the individual block of nerve is more appropriate, the circular injection (ring block) around the metacarpus gives most satisfactory anaesthesia. The local anaesthesia is injected in a transverse plane through the whole extremity to produce regional anaesthesia. The application of tourniquet above the site of injection has proved useful; in achieving better anaesthesia. The injection of local anaesthetic between the bone and the suspensory ligament should be restored to achieve most satisfactory anaesthesia of the digits. The anaesthesia of median and ulnar nerve is useful on the volar and medial aspect of the lower part of the forearm and carpus. However, for operation on the dorsal and lateral surface of the carpus and the lower forearm, anaesthesia of the branch of musculocutaneous and the radial is essential. To completely block the whole digit in bovines, four nerves need to be blocked. About 5-10 ml of 2% lignocaine is deposited at each site

Median nerve block: Site : Just below the radial tuborisity on the middle aspect in a groove in front of radius exatly at its middle. The lateral branch of the median nerve is blocked by giving a single injection in the midline just above the fetlock. The medial branch of the median nerve is blocked by giving single injection 5 cm above the fetlock on the inside of the limb in the groove between suspensory ligament and the flexor tendon and 10 to 12 ml of 2% lignoicaine hydrochloride is injected.

Ulnar nerve block: Site: A hands breadth above the accessory carpal bone between flexorcarpi radialis ulnaris lateralis on the postero lateral aspect of forearm. The dorsal branch of the ulnar nerve is blocked about 5 cm above the fetlock on the lateral aspect of the limb in a groove between the suspensory ligament and the metacarpal bone. The volar branch of the ulnar nerve is also blocked at this point since both the nerves are situated in front and behind the suspensory ligament . Radial and musculocutaneous nerve block at the metacarpus: A point 5 cm above the fetlock on the dorsomedial aspect of the metacarpus is selected. The needle is introduced at this point beneath the fascia. Three injections of nearly 25 ml of 2% lignocaine hydrochloride are given adjacent to each other. The dorsal metacarpal nerve a superficial branch of the radial nerve and is blocked at about middle of the metacarpus, medial to the medial digital extensor tendon. The medial palmar nerve, a continuation of the median nerve and is blcoked at the medial aspect of the superficial tendons in the groove between the suspensory ligament and superficial flexor tendon. The dorsal branch of the ulnar nerve and the palmar branch of the ulnar nerve are blocked about 5 cm above the fetlock, dorsal and palmar to the suspensory ligament, respectively, on the lateral aspect of the limb. About 5 ml of 2% lingocaine is deposited at each site.

Nerve blocks of the hind limb: Complete anaesthesia of the digital region of the hindlimb of bovines can be achived by blocking the superficial and deep peroneal, and medial and lateral plantar nerves. About 5-10 ml of 2% lignocaine is injected at each site.

Superficial peroneal nerve is blocked at the dorsal surface of the proximal third of the metatarsal bone. To block the deep peroneal nerve, a 2.5 cm long needle is inserted full length at the junction of mid and distal third of the metatarsal region and directed medially so as to pass under the extensor tendons The blocking of the tibial and common peroneal nerve above the hock produces analgesia from the fetlock downwards. The most important advantage of the technique is that the limb does not become paralysed completely and bears the weight. Most of the lower limb is rendered analgesic.

Tibial nerve block: The tibial nerve is blocked about 10 cm above the tuber calcls on the medial aspect in the groove between Achilles tendon and deep flexor tendon. The point of the needle is introduced anterior to Achilles tendon beneath the fascia. About 20 to 25 ml of 2% procaine hydrochloride is injected at the site and the anaesthesia is obtained within 10 to 15 minutes.

Peroneal nerve block: The peroneal nerve is blocked before it divided into deep and superficial peroneal nerves between extensor pedis and flexor metatarsi muscles. The needle is introduced obliquely superficially downward and forward at a point immediately behind the posterior edge of the lateral condyle of the tibia. Analgesia develops within 10 to 15 minutes after the injection of 15 to 20 ml of 2% procaine hydrochloride. The blocking of superficial and deep peroneal nerves independently helps in the desensitization of the area below fetlock joint in the hind limb. A subcutaneous injection of about 8 ml of 2% procaine hydrochloride is made halfway down in a groove on the anterior aspect of the metatarsal below extensor tendon (Fig.13). About 8 ml of 2% procaine hydrochloride is injected.

Medial and lateral plantar nerve block: The medial and lateral plantar nerves are blocked in a depression nearly 5 cm above the fetlock joint between the suspensory ligament and flexor tendon. About 7 ml of 2% procaine hydrochloride solution is injected deep to the superficial fascia. The lateral plantar nerve is blocked on the lateral aspect at the middle of the metatarsal bone, between the suspensory ligament and flexor tendons. The medial plantar nerve is blocked at the same level on the medial side. About 10 ml of lignocaine is injected at each site.

Regional anaesthesia of the limbs: A 15 cm long needle is inserted from the angle of the jaw towards the mandibular foramen. The point of needle must penetrate a distance of 10 to 15 cm and 10 to 15 ml of 2% procaine hydrochloride is injected. A successful block desensitizes the lower jaw with its teeth and the lower lip. (Fig.8)

Lateral. 1.Proximal volar nerve (Proximal part of lateral branch of median nerve). 2.and 3. Distal volar nerve (Distal part of lateral branch of median nerve)

Medial 1.Median nerve. 2.Ulnar nerve. 3.Proximal volar nerve (Proximal part of medial branch of median nerve) 4.and 5. Distal volar nerve (Distal part of medial branch of median nerve). The palmar (volar) and plantar nerves are most frequently blocked for the diagnosis of lameness. The volar and plantar nerves provide sensibility to digits. According to the site of injection, they are classified as high and low volar or plantar and subcarpal palmar. The volar and plantar nerves follow the borders of the deep flexor tendon down to the fetlock joint in company with the digital artery and vein.

High volar or plantar block (Proximal plantar nerve): The nerve is situated in a groove between the borders of suspensory ligament rostrally (anterorly) and deep flexor tendon caudally. The site of injection is 5 to 7 cm above the fetlock joint in the above groove, where the nerve is enclosed in a common sheath along with artery and vein. The needle is inserted downward and inward behind the tendon up to the suspensory ligament. If blood escapes from the needle, it should be withdrawn slightly. The operator should make sure that the needle has been fully withdrawn from the vessel. 5 to 7 ml of 2% procaine hydrochloride is then injected slowly. When the nerve of both the sides of the limb has been blocked, similar technique is applied for the opposite limb. In the hind limb, similar procedure is adopted. However, the operator should be very careful. There is a great risk of injury. Therefore, the animal should properly be secured before undertaking the block. The full effect of block is achieved within 10 minutes. Any response to pricking with needle indicates failure of injection. The subcutaneous injection instead of subfacial injection is the probable cause of such failure. In such cases, a second and still deeper injection may be attempted. High Volar or plantar block is indicated for detection of the site of iameness. It is a therapeutic measure in the treatment of painful conditions above the foot, cotonet, heel and in conditions like corn, quittor and sandcrack. The planar neurectomy can safely be performed under high plantar block.

Low volar plantar block Distal plantar nerve: In low volar or plantar, the nerve is blocked midway between the fetlock joint and the coronet. The nerve lies in front of the deep flexor tendon. For location of site, the posterior border of the first phalanx is identified and the order of deep flexor tendon is palpated. The needle is introduced in front of the tendon and 4 to 5 ml of 2% procaine hydrochloride is injected. This block has very limited indications. However, it is very effective in the diagnosis of lameness due to navicular disease.

Medium nerve block: The nerve is best infiltrated at the neurectomy site. The nerve is readily palpable at 5 cm distal to the elbow joint on the medial aspect of the upper forearm. The needle is inserted obliquely about a hand’s breadth above the chestnut in a groove formed by ulnar and radial flexor of the carpus. The needle is then directed towrd the volar- lateral surface of the radius. The nerve is blocked by injecting 8 to 10 ml of 2% procaine hydrochloride.

Ulnar nerve block: The nerve is situated in the groove on the caudal aspect of the forearm between ulnaris lateralis and flexor carpi ulnars. The site for injection is hand’s breadth above the carpal joint in the above mentioned groove. The needle is inserted at a depth of 1 to 2 cm and to 10 ml of 2% procaine hydrochloride is injected.

Musculocutaneous nerve block: The needle is inserted on the medial aspect of the limb half way between the elbow joint and the carpal bone immediately in front of the cephalic vein. The nerve is situated between the cephalic the carpus. 8 to 10 ml of 2% procaine hydrochloride is injected.

Nerve block of the hind limb: The tibial, peroneal and plantar nerves are commonly blocked in the hind limb. For plantar nerve block in the hind limb, the technique is similar to that described for the fore limb.

Tibial nerve block: The nerve is infiltrated in a groove between the Achilles tendon and the long digital flexor, 15 cm above the point of hock. Injection is given deep into the subcutaneous tissue; the palpation of the nerve is easy with the foot raised and the leg slightly flexed. About 20 to 25 ml of 2% procaine solution is injected. Further, 5 ml of the same solution is injected during partial withdrawal of the needle to block the cutaneous branch of the tibial nerve.

Peroncal nerve block: The nerve is blocked in the groove between lateral digital extensor and long digital extensor tendons above the lateral malleolus. The needle is inserted 2 cm deep in proximal and oblique direction deep into the fascia and 10 ml of 2% procaine is injected. For simultaneous blocking of the superficial branch, another 10 ml is injected subcutaneously during withdrawal of the needle. By blocking the tibial and peroneal nerve, the posterior metatarsus, medial and lateral aspect of the fetlock and whole digit is blocked.

Digital nerve block: The digital nerve blocks are performed through medial and lateral approach to anaesthetized first phalanx of a particular digit. A fine needle is inserted subcutaneously on each side of the digit obliquely and 2 to 3 ml of 2% procaine hydrogen chloride is injected at the site (Fig.14).

Technique: 1.The posterior border of particular rib is palpated at junction of upper and middle 3rd at lateral border of back muscles. 2.a 7 cm long needle is inserted perpendicularly at posterior costal border and is directed downwards. 3.Needle is inserted along with rib and then contact with rib is maintained. 4.When needle is subpleural, injection is made and continued as needle is slowly withdrawn. About 20 to 25 ml of 2 % procaine is injected. Hissing sound indicates its entry into thorax or abdomen. Therefore, the needle should be withdrawn immediately. The area to be anaesthetized includes lower rib, intercostal muscles behinf the rib and skin.

REGIONAL ANAESTHESIA OF TRUNK

Paravertebral block: This is the regional anaesthesia or perineural injection of local anaesthetic solution of spinal nerves either canal at intervertebral foramen or more distally at the free ends of lumbar transverse processes or the posterior border of ribs dorsally. According, it may be ¾ 1. Proximal paravertebral 2. Distal paravertebral Both forms are used in cattle for laparotomy, rumenotomy, caesarean and partial resection of rib e.g. 9th rib to get into reticulum. Paravertebral has number of advantages.

Advantages of paravertebral block: 1.Abdominal wall including peritoneum is completely and uniformly desensitized. 2.It is possible to carry out operations on thorax and abdominal walls of large animals in standing position. Casting is thus avoided. 3.It produces minor changes, if any, on sympathetic supply of circulatory system, as compared to spinal anaesthesia. In epidural anaesthesia, sympathetic supply of entire anaesthetized area is paralysed whereas in proximal paravertebral anaesthesia the ramicommunicans of the sympathetic chain below the intervertebral foramen are blocked in the anaesthetized segment. Thus, the interference with autonomic system is much less and hence the danger of fall in blood pressure during paravertebral is much reduced. 4.The method is safe and quicker in effect. 5.Post surgical convalescent period is shorter and without complication. 6.Quantity of local anaesthetic required is less.

Disadvantage of paravertebral block: 1.Paravertebral, especially proximal is technically more difficult to perform. Thus, occasional failure may be expected when nerve trunks are not precisely located.

Paravertebral anaesthesia in cattle:

Distal paravertebral anaesthesia of thoracic wall: The indications of distal paravertebral anaesthesia of the thoracic wall in cattle are very few. The resection of 9th rib to approach the reticulum necessitates the blocking of 8th, 9th and 10th intercostals nerves. Although there are very few indications of median and paramedian incision anterior to the umbilicus on the abdominal wall, blocking of 9th to 12th thoracic nerves either unilateral or bilateral is necessary. The incision posterior to the umbilicus necessitates the blocking of 11th, 12th and 12th thoracic nerves. The area enclosed between supraspinatus muscle anteriorly, thoracic wall and the dorsal border of the brachiocephalicus muscle dorsomedially is identifies. Depression in the centre of this area is palpated along with the first rib. A 7 5 cm needle of 1.6 mm bore is inserted into the centre of the depression and is directed laterally, backwards to the chest wall and medial to the subscapular muscle until the point at the level with the spine of the scapula is reached. By aspiration, it should be determined that the needle has not penetrated through blood vessel. Injection of 10 to 15 ml of 2% procaine hydrochloride produced analgesia within 10 to 15 minutes. Forelimb distal to the elbow is anaesthetized by this block.

Distal paravertebral anaesthesia of abdominal wall: Nerves are situated beneath intertransverse ligament and penetration to this depth is not attended by any serious injury to subjacent structures due to psoas and quadraus muscles. Number of nerves involved will depend upon site of incision e.g. for incision parallel to and 7 cm from last rib, last thoracic (T13) and first (L1) lumbar nerves are enough. For caesaean by flank, blocking of first (L1) second (L2) and third (L3) lumbar nerves gives adequate anaesthesia.

Technique: In this form of anaesthesia T13 to L1 and L2 are usually blocked. To block the 13th thoracic nerve, the site of injection is 6 cm from spinous process lateral to mid line and cranial to 1st lumbar spinous process. The lumbar nerves are blocked by introducing needle 6 to 7 cm lateral to the centre of the corresponding spinous process. As an alternative method, an imaginary transverse line is drawn immediately behind the spinous process of particular vetebra (Lumbar). The needle is inserted at 5 cm (Farquarson) or 6 cm (Neal) on this line lateral to the mid line. The needle is inserted vertically (fig.16) penetrates intertransverse ligament, just behind the posterior border of transverse process at a depth of about of 5 to 6 cm. an 8cm long, 18 gauge needle is used and 8 to 10ml of 2 per cent procaine is injected under intertransverse ligament and about 5 ml along the tract at which needle is withdrawn. During final withdrawal, skin is pressed to prevent separation and entry of the air. Replacement with 2% lidocaine is found to give regular results. Failure is inevitable due to deep location of nerve and is also due to nerve traversing obliquely intertransverse space. It is difficult to keep the needle absolutely vertical. Assessment of the site of injection and depth is difficult. The penetration of back muscles tends to cause spasms and modifies direction of needle and nerve. When incision is very close behind costal arch, infiltration of 12th thoracic is helpful and anaesthesia is completed. If sensitivity still exists, infiltration along with the line of incision is performed.

Pudic (internal) nerve block in cattle. Although epidural is a reliable means of providing relaxation is a reliable means of providing relaxation of penis in bull, it is disadvantageous, especially in heavier animal and chiefly due to a large volume of anaesthatic solution required to cause completed relaxation of penis during anterior epidural. Anterior epidural causes revere motor interferences of hind limbs and pelvis. Prolonged recumbency in heavy animals often is associated with struggling and may cause injury elsewhere. Radial paralysis of temporary nature is known to occur due to prolonged recumbency and is serious as long as it lasts. The retractor penis muscle is very well developed in bull and is not generally possible to pull penis from prepuce for either catheterization for treatment and diagnosis of Trichomoniasis or Vibriosis or to maintain erct penis out of prepuce. Pudendal block thus produces relaxation of retractor penis muscle so that the penis is spontaneously prolapsed or in case of narrow prepucial orifice, it can be drawn out without resistance. Innervation of rectrator muscle of penis appears to be by sympathetic fibres also. Thus sympatholytic products like chlorpromazine produces paralysis of retractor muscle and penis prolapses in cattle and horses. Therefore, examination and superficial treatment of the penis may also be performed with aid of the drug having tranquilizing action. The pudic nerve is formed from the ventral branches of second, third and fourth sacral nerves. It passes downwards and backwards on the medial surface of the sacrociatic ligament. The pudic nerve crosses the lesser sacrociatic foramen along with pudic artery and vein along the floor of the pelvis to the ischial arch to supply motor tibres to urethra and retractor penis muscle.

Technique: A hallow point on either side or deepest in the ischiorectal fossa is selected. The ischiorectal fossa is formed by ischial tubersity (ventral), caudal border of sacrotuberous or sacrosciatic ligament (lateral) and rectum with coccygens muscle (medial). This ‘llollow’ disappears in fat bovine animals. The needle is inserted through this fossa and is directed medial to sacrotuberous ligament with hand inside the rectum. Although left hand can be used for palpation of both right and left nerves, the use of right hand facilitaties the palpation of left nerve. The pulsation of the pudic artery at a finger’s indication of localization of site of injection. The use of canula or large needle also is advantageous. The needle is guided with hand in side the rectum towards lesser sacrosciatic ligament which is located laterally. Preparation of insensitive weal at the site facilities the further introduction of needle. A 12 to 13 cm long needle is used which goes 5 to 7 cm deep in the tissue and close to the pelvic wall. At first site 20 to 25 ml of 2% procaine is injected. A little behind it 10 to 15 ml of the same solution is injected to block middle haemorrhoidla nerve which also carries some sympathetic fibres to penis. A 3rd injection of 10 to 15 ml is made after redirecting the needle a little ventrally just inside the lesser sacrosciatic foramen where ventral branch of pudic nerve can be palpated distal to anastomosis near obturator foramen. Avoid puncture if vein. Nearly 40 to 50 ml of 2% procaine is injected on each side. However, heavy bulls require double the dose. A proper surgical cleanliness throughout is a must. The pudic nerve block is easier in young bulls; however, palpation of the nerve with the hand inside the rectum is difficult in large size bulls. The relaxation of sigmoid occurs in 30 to 40 minutes. The duration of relaxation is 6 to 10 hours. In bull, method is more exacting, cumbersome and difficult than epidural, still overcomes prolonged recumbency of anterior epidural.

Indications: In male, it is indicated for paralysis of retractor penis and anaesthesia of perineum and penis. In female, it is adopted for anaesthesia of vulava, vagina and anus.

Blocking of dorsal nerve of penis in ox.

Technique: It is indicated for relaxing sigmoid flexure of penis. Site 1 ¾ The dorsal nerve of the penis is blocked by grasping the sigmoid flexur behind scrotum and is then drawn backwards. A 15 cm long needle is inserted to the side of 2nd curve if flexure by the side of penis shaft. It is further advanced anteriomedially until needle lies 10 cm deep on the dorsal surface of penis. Nearly 25 to 50 ml of 2 % procaine is injected at this point as well as after slightly withdrawing needle. Likewise, the other side is also blocked. Total requirement of solution varies from 50 to 100 ml depending upon the size of animal. The relaxation of flexure and prolapse of penis usually occur within 15 to 20 minutes but may take 48 to 60 minutes. Relaxation usually lasts for about 3 hours when penis is withdrawn within prepuce spontaneously. In young animal, glans alone appears as a rule, but body may be drawn by manipulation. Site 2 ¾ The lower part of sigmoid flexure is held in front of stifle with hind legs properly secured together. The needle is obliquely directed caudally until dorsal surface is reached on the outer surface of penis, and 100 to 120 ml of 2% procaine is injected.

Paravertebral anaesthesia in dog: The 11th, 12th and 13th thotacic and the first, second and third lumbar nerves on one or both sided are blocked.

Technique: A skin weal is made with a subcutaneous injection of 2 ml solution. To infiltrate the 11th thoraclc nerve, the 12th rib is palpated ventolateral to the longissimus dorsi muscle. The needle is inserted at the cranial border of the rib and pushed along craniomedially until it reaches the 11th thoracic vertebra slightly cranial to the invertebral foramen. The anaesthetic solution is then injected. The 12th thoracic nerve is blocked in a similar manner using the 13th rib as a land mark. A skin weal is made at the level of the vertebral end of the 13th rib lateral to the lower part of spinous process of the 13th thoracic vertebra. The needle is then inserted vertically at this point and directed cranially until it touches the caudal articular process of the 13th thoracic verteba. Then needle is withdrawn slightly and redirected towards the intervertebral foramen between the last thoracic and first lumba veretbrae. The anaesthetic solution is introduced in this region to block 13th thoracic nerve. The caudal border of the spinous process and the transverse process of the first lumbat vertebra are taken as the land mark to block the first lumbar nerve. A skin weal is made 2 to 3 cm lateral to the spinous process. The needle is penetrated vertically 2 to 3 cm lateral to the caudal border of the spinous process and medial to the caudal border of the transverse process of the first lumbar vertebra. It is then directed caudally untillit reaches the cranial articular process of the second lumber vertebra. The needle is withdrawn slightly and anaesthetic solution is injected in the region of the intervertebral foramen. A similar technique is adopted to block the second and third lumbar nerves, taking the caudal border of the spinous process and medial aspect of the caudal border of the transverse process of the second and third lumbar vertebrae as land marks. The whole procedure of blocking the nerves takes approximately 10 minutes. The average duration of the stage of desensitization is 45 minutes. The recovery takes place without any complication. Procaine hydrochloride (2%) solution is safely used as anaesthetic solution. For small size dogs 2 ml, average size dogs 3 ml and large size dogs 4 ml is injected at each site. It is indicated together with tranquilizers intramuscularly whenever general anaesthesia is reguarded as dangerous. In cases of nephrectomy, gastrotomy, enterotomy ovarohysterectomy, prostatectomy and excision of mammary tumours, paravertebral anaesthesia is useful.

CHAPTER 6 3. SPINAL ANAESTHESIA: It is a form of nerve trunk anaesthesia. The nerves are blocked either within or at their exit from the vertebral canal. The anaesthetic solution may be introduced into the space occupied by loose connective tissue, fat and venous plexus outside the tough spinal covering of dura mater (extradural or epidural) or into the cerebrospinal fluid filled (Arachnoid) space below the dura mater (Sub-dural).

SPINAL ANALGESIA This is the injection of local anaesthetic into some part of the spinal canal, and its contact with the spinal nerves and roots results in temporary motor paralysis and loss of sensation of the body area supplied by sensory nerve fibres. It was first developed by corning in dog in 1885 in U.S.A. Spinal analgesia may be divided into the following types¾ 1.Subarachnoid. The needle pierces through duramater and subarachnoid and injection of local analgesic is made in the cerebrospinal fluid. This is known as spinal anaesthesia in human being. 2.Epi or extradural. The needle enters into neutral canal but does not penetrate menings. The solution is deposited along the canal. It may be sub-divided into ¾ High ¾ Anterior or cranial, when injection is made anterior to sacrum or when injected anaesthetic solution reaches 2nd sacral or other cranial segments. Low ¾ Posterior or caudal, when injection is given posterior to sacrum or when solution does not reach the 2nd sacral segment. 3.Segmental. When epidural injection is made in small quantities and only few nerve roots of the site of injection are blocked. This could also be divided into ¾ 1.Subdural. 2.Epidural or peridural. In hymen medicine this is made posterior to the caudal end of the spinal cord. For injection the needle enters into vertebral canal through interarcual foramen and nerve roots are blocked as they leave spinal canal. These may be blocked either subdurally or epidurally depending upon the kind of injection. Dura mater is considered practically impermeable for local anesthetic solution, although some may diffuse through it and reaches cerebrospinal fluid. During epidural course, the nerves are covered with sheath of dura mater which is reduces distally. This sheath runs into epineurium at intervertebral foramen through which some solution passes outwards. In subdural or subarachnoid injextion, the anaesthetic solution mixes with and is diluted by cerebrospinal fluid and blocks subdural, dorsal and ventral nerve roots. However, the conductivity of spinal cord itself remains unaffected. In segmental anaesthesia, when anaesthetic is injected in small quantities epidurally, only a few nerve roots located near the site of injection may be blocked while cranial and caudal spinal nerves conduct normal impulses.

Action of spinal anaesthesia At onset, only loss of sensitivity to painful stimuli is observed. Later on, motor impulses are interrupted which is due to prompt penetration of anaesthetic solution into non-myelinated fibres. The sympathetic fibres of spinal nerves are also blocked resulting in loss of vasomotor tone in anaesthetized part and consequent vasodilatation, increased vascularlly and elevated skin temperature. The anterior (high) block generally produces reduced blood pressure which can lead to complete loss of circulatory control. If this anaesthesia extends cranially up to splanchnic nerve, a large volume of blood may accumulate around abdominal viscera due to loss of sympathetic tone. Usually fall in blood pressure (BP) is within safe limits and results in reduced haemorrhage in operative region, but if this occurs, steps to counteract peripheral circulatory reaction and transfusion of blood or blood substitutes should be taken promptly. However, in ruminants particularly, due to extensive and very vascular abdominal viscera, the fall of BP can be very considerable and usually needs proper treatment. Motor control inhibited through sympathetic system (in anterior or subdural block) results in increased peristalsis in small intestines and anterior part of colon but relaxes iliocaecal valve. The moderate anterior epidural anaesthesia blocks the sacral parasympathetic fibres which cause dilatation of anal and vulvar sphinctors and relaxation of penis. Uterine control can also be inhibited by anterior epidural. Pregnant uterus is unaffected as its contractions are largely under autonomous control.

Indications of epidural anaesthesia 1.All interferences posterior to diaphragm can be performed. 2.Obsterical and gynaecological manipulation in large animals. 3.Lapatomy in cattle and small animals. 4.Low epidural for interferences of anal, perineal and external female genital organs. 5.In old subject which can not withstand general anaesthesia epidural is advocated. 6.In conditions involving lung, kidney or liver damage when general anaesthesia is indicated, use of epidural is advocated.

Contraindications of epidural anaesthesia 1.Damage to vertebrae (lumbar or sacral) or spinal cord meninges. 2.Stenosis in vertebral canal. 3.Defect at injectionsite or in canal. 4.Lameness or paralysis of hind quarters of nervous origin. 5.Low blood pressure or circulatory collapse. 6.Loss in the body condition of serious nature e.g. debility, anaemia etc.

Onset of anaesthesia Maximum analgesia occurs between 5 to 20 minutes. The rapidity of onset varies with age and species. The onset of anaesthesia is rapid in sheep, calf, ox, pig and foal, It is less rapid in dog, cat and horse.

CATTLE Caudal epidural anaesthesia Both anterior and posterior caudal epidural can be carried out safely in cattle.

Technique: The injection is best made in the space between arches of 1st and 2nd coccygeal vertebrae. This is preferred to sacrococcygeal space as it is ¾ (a)Large and thus easily palpated and penetrated particularly in fat animals. (b)Easily detected because 1st coccygeal vertebra is usually firmly attached to sacrum but the 2nd coccygeal vertebra is freely movable. 1.When tail is raised and lowered in pump handle fashion after securing it from base, a definite depression is felt between 1st and 2nd coccygeal vertebrae. 2.The prominence on croup is of sacral vertebra and next highest part on the tail is the spine of the 1sy coccygeal vertebra, just behind it is the 2nd coccygeal vertebra. 3.A hand’s breadth anterior to the middle of a transverse line joining ischial tubers. 4.After palpating the posterior tuberosity of ischium, an imaginary line joining them is drawn which passes directly over the back. A point 4 to 41/2 cm in front of intersection on midline is taken for introduction of needle. The distance between surface of skin and floor of spinal canal is usually 2 to 4 cm. use of 16gauge and 41/2 to 6 cm long needle is recommended. The tail is allowed to hang naturally. All aseptic precautions are to be taken in perpetrating the site of injection. After proper shaving and disinfecting the site, an insensitive skin weal is made by injecting 2 ml of 2 % procaine hydrochloride. The needle is then inserted downwards and forwards at 450 vertically. Occasionally, animal may shiver suddenly due to contact of needle with coccygeal nerves. If position and direction of needle is proper then no resistance to injection is offered. The needle is introduced 11/2 to 21/2 cm deep depending upon the size of animal. Occasionally, blood may escape through needle. If this happens, the needle should be withdrawn and reinserted. The introduction of local anaesthetic into circulation causes blood borne toxicity. The injection of solution should be slow taking nearly 15 seconds in injecting 15 ml. About 2 percent solution is suitable for obstetrical manipulations as well as for painful cutting. The epidural cavity is occupied by semi fluid fat which does not serve as diluent for concentrated solution. The vasoconstrictor actions of adrenaline on subcutaneous tissue is much different than epidural, because nerve trunks are much less vascular than skin or subcutaneous tissues. Practical observations in this regards are confusing. Some workers feel that additional vasoconstrictor delays onset and others think it hastens and intensifies action of anaesthetics. However, the use of adren aline may be of advantage as it may stimulate sympathetic fibres. Adrenaline affects only postganglionic fibres, whereas in epidural space it contacts only preganglionic and so the absorption would be slow.

Posterior (low) block: In this block, the motor control of the hind limbs is uninfluenced. Analgesia of the skin over the tail, croup up to mid sacral region, anus, vulva, perineum and the posterior part of vagina develops. There is relaxation of anal sphincter and defaecation will be suspended. Nearly 8 to 15 ml of 2% procaine with or without adrenaline is used in different animals. In small sized animal 12 ml and large sized animal 15 ml of this solution can suitably be used for posterior block. In parturition cases, straining ceases but uterline contractions continue.

Indications: 1.Obstetrial ¾ Overcome straining while manipulation and correction of malpresentation, simple embryotomy, operative treatment of parturient injuries, reduction of prolapsed uterus and vagina. 2.General ¾ Operations of tail; Perineum, vulvar tears, examination of vagina or os, retraction of uterine cervix. Onset of the anaesthesia starts within 1 to 2 minutes. Muscular paralysis of tail gives reliable evidence of correct injection. Maximum effect is noticed within 20 minutes. The duration of analgesia is for about 1 hour and three after progressive recovery follows.

Anterior (high) block: In this block some degree of motor control of the hind quarters remains paralysed. The area of anaesthesia includes tail, anus, rectum, vulvaand vagina, perineum, and hind quarters and abdominal wall. Head should be placed high as to avoid cranial diffusion with possible paralysis of medulla. For anterior epidural anaesthesia the recommended dose varies between 30 to 150 ml depending on the size and type of operation. For difficult embryotomy, malpresentation and castration by open inethod the dose of anaesthesia varies from 40 to 80 ml for small, medium and large size animals. However, for caesarean section and amputation of udder as well as for digits, the recommended dose varies between 60 to 120 ml for small, medium and large size animals. The following points will be useful in achieving maximum effect of anterior block with minimum complications. 1)The degree of motor interference varies with dose from partial paralysis of flexors and extensors of joints to complete paralysis. 2)Enough bedding should be provided to avoid injuries. 3)For bilateral anaesthesia it is helpful if the animal is kept on breast with hind limbs underneath for 10 to 15 minutes to ensure bilateral effect. 4)For unilateral analgesia, animal should be restrained with its appropriate side downwards until full effect of analgesia follows. The animal should then be turned over. 5)The loss of sensation spreads progressively forwards finally reaching flank and umbilicus. 6)The animal is unable to rise for 2 hours or so and the in coordination of hind legs persists for 3 hours or even longer. 7)When full anaesthesia is attained it is better to keep animals well secured to avoid serious injures from efforts to rise before full motor functions of hind limbs return. A constant control on the head is essential. Tail serves as a good guide of recovery from anaesthesia.

Indications

Obstetrical ¾ Difficult manipulation, repositioning during dystokia, extensive embryotomy, amputation of prolapsed uterus and rectum and caesarean section.

General ¾ Examination and operation of penis, prepuce and inguinal regions, castration and operation in udder, hind limbs e.g. amputation of digits, exploratory laparotomy, and ruinenotomy. The use of chloral hydrate orally is a good complimentary anaesthesia. The onset and duration of anaesthesia is as in posterior epidural.

Accidents and complications of anterior block When properly used, it is entirely free from danger. Surgical cleanliness is a must and proper sterilization of syringes, needles as well as anaesthetic solutions is necessary. 1)Occasional lameness due to sudden fall is sometimes observed in heavy animals. 2)Twisted tail for 5 to 6 days with normal mobility or permanent paralysis of tail after injection may be due to damage to coccygeal nerves. 3)The paralysis of tail accompanied with a sinus is probably due to infection of canal, although it is a rare condition. 4)The small vials of anaesthetic should be used when dealing with dead putrefied tissues, fetuses or vaginal examination of large size containers. 5)Occurrence of hypotension is due to the effect of anaesthetics on sympathetic system and vasodilatation.

Lumbar epidural anaesthesia One single injection of local anaesthetic in anterior lumbar region causes anaesthesia of both of the flanks and animals is able to maintain standing position. It is useful for caesarean section and rumenotomy in standing position. About 10 to 12 ml of 2$ procaine solution is sufficient to desensitize sublumbar region in average size animal. However, when the dose exceeds 15 ml the weakness of the hind quarters is seen and the animal is unable to stand. The use of 10 ml of 2% lignocaine gives satisfactory results.

Technique An insensitive skin weal is produced with a fine needle to facilitate penetration of spinal needle. Then 14 gauge 12 cm long needle is introduced on the right of the lumbar spinous processes on a line 1.5 cm behind the anterior edge of the 2nd lumbar transverse process. The needle is then directed downwards and inwards vertically at 10 to 130 for 7.5 cm. The penetration of interarcual ligaments is painful and so animal be effectively restrained at head before penetration of needle is attempted. The solution is injected epidurally. The effect is obtained in about 10 minutes and persists for about 3 hours.

Complications Following complications are some times notices after limbar epidural anaesthesia in cattle. 1)Partial paralysis of left anterior crural and obturator nerves which results in dropped still with abduction of limb and with tencency to fall on the left side. 2)Unilateral anaesthesia may develop on left side and is usually due to insufficient volume of anaesthetic. This is seen by pronounced bending of spine with convexity of the curve on desensitized side. 3)Urine passes within few minutes of onset, which are probably due to paralysis of sympathetic fibres controllong the trigonum vesicae. 4)Skin temperature increases behind the site of injection by 40 F.

THE HORSE

Epidural anaesthesia has not been very commonly used in horses because less interference in horse requires it. Horses are unsuited temperamentally for a puncture near hind legs. The epidural anaesthesia is technically more difficult in horses and it is not easy to locate the site. The space between 1st and 2nd coccygeal vertebrae or first intecoccygeal space is preferred. The site of injection is assessed by following methods. 1)The first intercoccygeal space is usually felt by the fingers by raising the tail and is roughly 2.5 cm in front of basal tail hairs. However in fat animals, spines are not easily felt. 2) The space is opposite to caudal folds which are seen on either side of the base of tail when tail is raised. 3)When an imaginary line is drawn by joining two hip joints, it passes over the sacrococcygeal space. Immediately behind this the spinous process of the first coccygeal vertebra is felt. The depression posterior to it is the inter coccygeal space between 1t and 2nd coccygeal vertebrae. Restraining by twitch or rising fore leg is necessary. A slight reflex jerk in hind quarters may occur when needle contacts the nerve ends.

Posterior (low) block The depth of neural canal from the surface of the skin is nearly 4 to 6 cm. A 6 to 10 cm long needle with 2 mm diameter is used. After preparing an insensitive skin weal, the needle is passed through the skin in the middle of the space and forwarded until the floor of the canal is struck. When point of needle enters the vertebral canal a hissing sound is usually heard. About 10 to 15 ml of 2% procaine causes anaesthesia of tail, anus, rectum, perineum, vulva and vagina and eliminates abdominal straining. However in some cases when given standing, interference may give alarming symptoms or injury due to falling. For obstetrical manipulation, 15 to 25 ml of 2% procaine hydrochloride should be adopted depending upon the size of animal.

Anterior (high) epidural It is not usually recommended in horse, but may be used for extensive embryotomy, scrotal hernia or cryptorchidism. The animal must be sedated and restrained well before anterior block is attempted. Such resistant are maintained for at least 3 hours to ensure that the animal does not injure should be given very slowly (less than 20ml/min) to avoid clonic spasms and opisthotonus from increased pressure in the cerebrospinal fluid due to larger quantities of injectable solution in the epidural space. The animal should stand on its own before anterior block is attempted. For extensive obstetrical interferences, 50 to 120 ml of 2% solution of procaine hydrochloride is recommended. For surgical interferences, 30 to 80 ml of 2% solution is useful as per size of animal.

Lumbosacral epidural (subarachnoid anaesthesia) The subarachnoid anaesthesia is very rare in equine practice. However, the animals must be sedated adequately to control excitement associated with an attempt to stand. This anaesthesia should be used only when general anaesthesia is not possible or due to certain anatomical deformities at tail basement of sacroccygeal site. A point in the mid line of an imaginary line joining the two tubers of llia and 1 cm anterior to midpoint of space between spinous process of the last lumbar and 1st sacral vertebrae is selected. A 14 cm long needle measuring 2 mm diameter is introduced vertically up to the depth of 11 to 13 cm until loss of resistance is observed. The cerebrospinal fluid must either run through needle or be aspirated prior to injection of anaesthetic. The anesthesia is given in the subarachoind space with very slow speed. About 4 to 6 ml of 2 % procaine hydrochloride is used. The anaesthesia of abdominal wall and hind quarters is achieved within 1 to 2 minutes.

THE DOG

The spinal analgesia in dog comprises the injection of local anaesthetic into sacrococcygeal or intercoccygeal space as well as into lumbosacral space. The spinal cord in dog ends at the junction of 6th and 7th lumbar vertebrae and the meanings continue up to the middle of the sacrum.

Sacrococcygeal or intercoccygeal anaesthesia (caudal epidural) The sacrococcygeal or intercoccygeal space between last sacrum and 1st coccygeal or between 1st and 2nd or 2nd and 3rd coccygeal are used. The animal is best restrained on its back to avoid effect on splanchnic nerves during the onset period. For location of site tha tail is moved vertically with one hand and the other hand is used for palpation of intervertebal space which is evident due to depression. Technique A fine 4 to 6 cm long needle is introduced exactly in the middle on one of three spaces and is directed forwards and downwards. It is necessary that the needle should be maintained exactly in the midline at an angle of 300 when the needle is pierced through the interarcual ligament into the vertebral canal, resistance is immediately reduced. In very fat dogs, location of site is difficult. About 1 to 2 ml of 2 per cent procaine hydrochloride is useful for anaesthesia for tail, anus and perineum. For puppies, 0.5 to 1 ml of 2 per cent procaine is advocated.

Lumbosacral epidural anaesthesia Location of lumbosacral space is easier and the space is comparatively larger hance preferred. It is advantageous to rest the dog in cast position and then drew the hind legs forwards as far as possible to increase the space.

Technique For more precise location of site, an imaginary line joining the iliac prominences on either side is drawn which crosses the spinous process of the last lumbar vertebra. Space immediately behind the process is the lumbosacral space. About 4 to 8 cm long with 20 gauge needle is used for preparation of an insensitive skin weal by injection 1 ml of 2 per cent procaine hydrochloride. The spinal needle is then introduced in the midline immediately behind the last lumber spinous process and directed downwards and forwards. The needle usually strikes with the body of the last lumbar vertebra. Taking this as a guide line, the needle is slightly withdrawn and redirected downwards and backwards.

Dose and indications Dose of local anesthetic varies according to the size of dog. For small sized dog, 2 to 3 ml of 2 percent procaine hydrochloride is sufficient. However, for middle size, the dose vary between 7 to 8 ml. for large sized dog, the dose may exceed more than 10 ml. it may be mentioned here that whenever the dose is to exceed more than 9 ml, it should be done with care. In no case the dose should increase more than 11 ml.

The selection of dose also depends upon the type of surgical interference. For amputation of tail and return of prolapsed rectum, vagina or uterus as well as for suturing of teared perineum and removal of vaginal sarcoma, half the recommended dose is necessary. For operations on hindquafters like setting of fracture and dislocation, as well as surgery on posterior abdominal and inguinal regions for mammary tumours, laparotomy, hysterectomy and cystotomy, maximum dose is advocated.

The site of a sedative along with spinal anaesthesia is a good complimentary anaesthesia.

Complications of epidural anaesthesia 1) Hypotension is a common symptom if large quantity is injected with great speed. 2) Permanent injury to hind parts of the body may occur due to injury of caudal equine. 3) Complete motor paralysis may develop. 4) Sepsis for want asepsis. Advantages of epidural anaesthesia 1) Absence of respiratory distress in cases of branchicephalic breeds of dogs. 2) Complete muscular relaxation. 3) Absence of straining when peritoneum is subjected to traction. 4) Absence of depression of fetuses in caesarean section. 5) Absence of maternal morality when used for caesarean section.

THE PIG

Spinal cord in the pig ends at junction of 5th and 6th lumbar but meninges continue up to midsacrum. In adult, spinal canal is 1.5 cm anterioposteriorly, 3 cm wide and about 2 cm deep at lumbosacral space. There is slight risk of subdural puncture in pigs. The site is easily palpable in young subjects but may be difficult to locate in large fat animals.

Technique Procaine hydrochloride 2% is used as an anesthetic at the rate of 1 ml per 4.6 kg body weight. A 1 cm long brook’s lumbar puncture needle is used for the epidural injection. The following relationship between tail base and lumbosacral distance and depth to which needle penetrates to reach the spinal canal of animals of different body weight is recommended.

Weight groups (in kg) Tail base lumbosacral Distance (in cm) RANGE AVERAGE Deepth to which needle penetrates (in cm) Range Average

15-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 7.5-8.5 9.0-10.5 10.5-12.5 12.0-13.5 13.5-15.0 14.5-16.0 16.0-17.0 17.0-18.0 8.2 9.8 11.5 13.2 14.16 15.5 16.3 17.5 3.5-4.5 4.5-5.5 5.0-6.0 6.0-7.0 6.5-7.5 7.0-8.0 7.5-8.5 8.0-9.0 4.3 4.9 5.6 6.5 7.0 7.5 7.9 8.5 Location of the site is easier in animals below 30 kg. Anterior border of the llium is felt on each side. An imaginary line is drawn joining the anterior border of the last lumbar vertebra. About 2 to 3 cm caudal to the spine, a depression is felt. The needle is inserted in the depression in mid line and is directed downwards at an approximate angle of 450. If the point of needle strikes the caudal end of the spine of last lumbar vertebra, the needle is slightly withdrawn dorsally and redirected ventrocaudally so as to reach the vertebral canal and the solution is injected. However, it is difficult to ascertain this space in animals weighing 30 kg and above. In such animals, the needle is inserted at variable depths and points according to body weight (as mentioned in table) on mid line cranial to base of the tail to reach the spinal canal. The injection is then made slowly and animal is kept under constant observation for respiration, heart rate and general behavior. In majority of cases onset of anaesthesia is within 10 minutes. In most of the cases effect of epidural anaesthesia lasts from 11/2 to 2 hosts. There is complete paralysis of tail, relaxation of anus, desensitization of scrotum, tests and spermatic cord. The whole abdominal wall is desensirized. Complications due to spinal anaesthesia in pigs include laboured breathing, arched back, muscular tremors, uneasiness, gnawing and vigorous padding movement of the fore legs. Heart sounds are feeble and irregular. Sublumbar anaesthesia in pigs is indicated for operations of hind quarters, laparotomy, casration, common obstetrical manipulation, return of prolapsed rectum, amputation of prolapsed uterus, umbilical hernia and caesarean section. THE SHEEP AND GOAT

Caudal epidural anaesthesia The administration of local anaesthetic at sacrococcygeal space provides excellent analgesia for tail, anus, rectum, vulva, vagina, perineum, hind quarters and abdominal wall. It is an effective aid for difficult obstetrical manipulation, emnryotomy, caesarean, abdominal hernia and amputation of mammary gland. In cases of dystokia, constant straining of animal is very effectively checked without interfering uterine contractions.

Technique The space between last sacrum and first coccygeal is selected for epidural anaesthesia in sheep and goat. A depression nearly 0.5 cm behind the dorsal medial sacral crest is selected. A 4 cm long needle is introduced vertically which is then directed anterioventrally reach vertebral canal. About 4 to 6 ml of 2% procaine hydrochloride is pushed slowly to provide posterior epidural block. For anterior epidural block, 8 to 12 ml of 2% procaine should be administrated. Diffusion of the solution towards head should be avoided by keeping the head at a higher level.

Lumbar epidural anaesthesia Epidural anaesthesia is given through lumbo-sacral space. An imaginary line joining the anterior border of the illium on each side is drawn. This line crosses the spinous process of the last lumbar vertebra, the depression immediately posterior to which is the site of injection. The goat is restrained in standing position and fore and hind legs are held firmly. After preparation of site an insensitive weal is prepared by injecting 2 to 3 ml of local anaesthetic solution with very fine needle. A 20 gauge 4 cm long hypodermic needle is inserted through the skin and interarcuate ligament to reach to the epidural space avoiding penetration of dura mater. The needle is maintained exactly in the mid line and directed downwards and forwards maintaining the angle between 100 to 150 with horizontal axis of the body. The volume of local anaesthetic solution varies from 6 to 15 ml of 2% praocaine hydrochloride or lignocaine hydrochloride. However liganocaine is preferred. The indications for administration are similar to those described for caudal epidural anaesthesia in goat.