REGIONAL ANALGESIA

II-Subarachnoid AnalgesiaThe subarachnoid space can be easily reached from the lumbosacral

intervertebral space in all animals. The technique is similar to the epidural space, but the needle is more deeper inserted and aspirated for cerebrospinal fluid (CSF) to verify the position. Small dose of local analgesic about 1.5 to 2 ml of lignocaine 2% is enough for desensitizing a wide abdominal segment.

Accidents and Complications associated with the spinal analgesia

1) Infection of the neural canal is always a potential danger when spinal analgesia is used.

2) Injury of the caudal nerves during injection. There may be permanent paralysis of the tail in some cases after epidural injection.

3) Severe hypotension may develop, especially if complete anterior blockade is attempted. Hypotension may be combated by intravenous or intramuscular injection of vasopressors.

4) Injures of the pelvic limbs (fracture of the pelvis, luxation of the hip joint, etc…), so plenty of bedding should be supplied to avoid damage.

*Continuous Spinal AnalgesiaBoth continuous epidural or subarachnoid injection can be performed,

after the catheterization of respective space. The technique requires the use of a unidirectional pointed spinal needle (curved tip needle) and stiff catheter-stylet unit to catheterize the epidural or subarachnoid space from the lumbosacral space. The catheter can be directed cranially or caudally according to the desired effect and then fixed with adhesive tape after removal of the needle. In this technique the injection of the analgesic can be repeated. Continuous spinal analgesia can be performed in large and small animals.Continuous Segmental Epidural Analgesia After Catheterization of the Epidural Space

Posterior (sacro-coccygeal) and anterior (thoracolumbar) epidural block in farm animals can be induced by using epidural catheter implanted into epidural space at lumbo-sacral intervertebral junction. The interarcual space between the last lumbar and the sacrum is a reliable site for catheter implantation. It is larger than that of the sacro-coccygeal or the first intercaudal space and thus greatly facilitates the technique.

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In this technique unidirectional spinal needle with stylet and epidural catheter, which is closed distally, and with side openings should be used. The spinal needle is inserted along the median plane at the lumbo-sacral intervertebral space. The tip of the needle is directed 5-10 from perpendicular to the spinal cord and slowly advanced with bevel pointed cranially in case of thoraco-lumbar epidural block or caudally in case of sacro-coccygeal epidural block, until the epidural space is identified.

The stylet is removed from the spinal needle. The desired length of epidural catheter is advanced through fixed spinal needle until its tip is positioned at last thoracic 1st or 2nd lumbar vertebra (in case of segmental thoraco-lumbar epidural block) or at 1st or 2nd caudal vertebra (in case of posterior epidural block). The spinal needle is removed and the epidural catheter is fixed in situe by means of adhesive tape. An initial dose of local analgesic solution is injected slowly (1 ml/one minute) and for continuation of the analgesia about half the initial dose is given immediately upon return of sensation.

Initial Dose of Local Analgesic (2% lignocaine Hcl) for Segmental Epidural Analgesia:

Cattle: 5-7 mlHorse: 3-5 mlDonkeys: 2-3 mlOvine: 2 ml

Analgesia is developed within 5 minutes and persists for about one hour and can be maintained for another 40 minutes by fractional bolus of half initial dose.

For perfect epidural catheter implantation, certain precautions must be taken into consideration:

1) The site of spinal needle puncture must be aseptically prepared. 2) The use of unidirectional spinal needle (curved tip touhy cannula) to

catheterize the epidural space permits the catheter tip to make 90 fixation at the L-S intervertebral site and facilitates its cranial or caudal advancement without resistance.

3) Before insertion of an epidural catheter, a routine part of the procedure should include checking to assure the holes in the catheter are patent. This is particularly important for catheter without stylet whose holes can be obliterated.

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4) Epidural catheter must pass easily forward through the curved tip spinal needle and once the catheter had been advanced beyond the tip of the needle, its withdrawal through stationary needle is avoided to prevent shearing off the catheter which act as foreign body in the epidural space.

5) If repositioning of the needle is necessary after catheter passage, withdrawal is performed by moving the needle and the catheter as a single unit.

6) Absence of aspiration of CSF and blood is essential in ruling out inadvertent subarachnoid or intravenous injections.

There are Many Advantages of this Technique:1) The landmarks for determination of the injection site are definite and can

be easily located.2) Asepsis is easily maintained by the accessibility of the surgical area.3) The technique promotes analgesia of the abdominal wall without

interfering with the loco-motor control of the pelvic limbs and dangers of forcible casting are avoided.

4) Continuation of analgesia for prolonged operations can be easily induced by fractional bolus of local analgesic.

Possible Complications of Epidural Catheter are:1-Misdirection of the catheter and possible unilateral analgesia.2-Shearing off of the catheter by the sharp tip of the spinal needle.3-Catheter occlusion or kinking.

3-Intravenous regional analgesia

Intravenous regional analgesia (IVRA) is an important advance in bovine surgery of the last 30 years. IVRA produces excellent analgesia of all structures distal to the tourniquet that is applied prior injection. A further benefit is that the operation site does not undergo distention due to haematoma and oedema formation, which result from local infiltration of anaesthetic solution. The volume of anaesthetic solution injected in IVRA is often smaller than that used in other techniques. The technique is less time- consuming and requires only a single injection site. In addition, the possibility of tissue trauma and contamination is lessened. Yet IVRA has not been widely adopted because many practitioners fear that it requires unusual dexterity to inject a peripheral vein in a cow. However, once this technique has been used successfully, few veterinarians revert to the comparatively difficult and ineffective techniques of local infiltration and nerve blocks.

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Indications:The indications for IVRA include digital amputation, the removal of

interdigital skin hyperplasia, such as corns and fibromas, suturing of skin lacerations, and the exploration of deep digital sepsis where curettage is indicated.Technique:

Sedate the patient with xylazine at 2ml/400kg BW, intravenously. Then place the animal in lateral recumbency with the affected digit uppermost. Using a minimum of five turns, apply a tourniquet over the proximal metatarsus/ metacarpus or immediately proximal to the hock or carpus. If the tourniquet is placed above the hock, first insert two firmly rolled 4-inch bandages into the depressions between the calcaneal tendon and the distal tibial shaft, medially and laterally. These bandages will increase the local pressure on the soft tissue.

Wrap the tourniquet so tightly that is impossible to insert a finger between the tourniquet and skin.

Next, palpate the area of the distal metatarsus or metacarpus to identify any prominent superficial veins. It is helpful identify a section of superficial vein about 10 cm long.

In hind limb it is preferred to inject the abaxial proper planter vein, running obliquely planter to dorsal about 5cm proximal parallel to the common digital extensor tendon. An alternative hind limb site is the saphenous vein just proximal to the hock laterally.

In the forelimb, the large and prominent cephalic vein, which lies medially over the distal surface of the radius, is easy to access when the tourniquet is placed over the mid-radius region. The alternative vein in the forelimb, if the tourniquet is placed distal to the carpus, is the medial superficial metacarpal, lying over the deep flexor tendon distal to the carpus.

Other veterinarians injecting either a forelimb may prefer the dorsal common digital vein, which runs superficially in the median plane just proximal to the level of the proximal inter-phalangeal joint. One advantage of this distal site is that the tourniquet may be placed just above the fetlock.

Clip and disinfect the skin over the selected site. Fill a 20- or 30-ml syringe with 2% lidocaine (without epinephrine). Attach the syringe to a 20-gauge, 2.5 or 3.5 cm needle. Insert the needle proximal into the vein. To avoid displacement when the cow moves, firmly hold the needle shaft in position against the skin.

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Inject the lidocaine as rapidly as possible. A perivascular injection is immediately recognizable as a subcutaneous bump. In such a case, enter the vein again at 3 or 5 cm more proximally. Following injection, briefly and gently massage the site.

It is advisable to wait 5 to 10 minutes for the full development of analgesia, which usually occurs first near the coronary band and last in the interdigital space. The reason for this regional difference is not known, Analgesia persists for a minimum of 90 minutes, which is the safe period without peripheral gangrene.

Release the tourniquet upon completion of surgery, haemostasis and bandaging. Massage the skin at the tourniquet site for a few seconds after removing the tourniquet to reduce the local oedema. Toxicity problems related to the local anaesthetic entering the circulation have not been observed.

N.B. IRVA can be also used in small ruminants and dog.

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