Paravertebral nerve block in animals

paravertebral nerve block in animals

1. Topic : paravertebral nerve block

2. PARAVERTEBRAL NERVE BLOCK A paravertebral block is essentially a unilateral block of the spinal nerve, including the dorsal and ventral rami, as well as the sympathetic chain ganglion. These blocks can be performed at any vertebral level . ParaVertebral Block (PVB) involve injection of local anaesthetic in a space immediately lateral to where the spinal nerves emerge from the intervertebral foramina. This technique is being used increasingly for not only intra-operative and post-operative analgesia but also as a sole anaesthetic technique for carrying out various procedures.

3. CONT.... Several features of local anesthesia render it particularly useful in veterinary practice. • Many surgical procedures can be carried out satisfactorily under local anesthesia (e.g., C section in cows). • Whether or not sedation is necessary as an adjunct will depend on the species,temperament and health of the animal, and on the magnitude of the procedure. • In adult cattle, many operations are performed on standing animals and since sedation may induce the animal to lie down, it is better avoided. Enabling operation in standing animals also eliminates the dangers associated with forcible casting and restraint, and prolonged recumbency.

4. MECHANISM OF ACTION OF LAs Mechanism of action • LAs block nerve conduction by inhibiting influx of sodium ions through ion-selective sodium channels in nerve membrane leading to impairment of the generation of action potential. • The sodium channel itself is a specific receptor for local anesthetic molecules .

5. CONT... Spinal nerves exiting the spinal cord run caudally beneath the transverse processes of the lumbar vertebrae. After emerging from the foraminae of the spinal column, the spinal nerves divide immediately into a small dorsal branch, which supplies skin and muscle of the loins, with some supply cutaneously down the flank, and a ventral branch which runs obliquely down and back between the muscles, providing the main nerve supply to the flank (skin, muscles and peritoneum) .

6. CONT... The 13th thoracic nerve passes cranially to the transverse process of the first lumbar vertebra (L1); the ventral branches of the lumbar nerves each run obliquely, just below the intertransverse ligament, across the space between the transverse processes . The paravertebral block involves perineural injection of local anaesthetic solution around the spinal nerves as they emerge, through the intervertebral foramina, from the vertebral canal.

7. TYPES.. 1: PROXIMAL PARA VERTEBRAL NERVE BLOCK. 2:DISTAL PARA VERTEBRAL NERVE BLOCK.

8. PROXIMAL PARA VERTEBRAL NERVE BLOCK(PPVN) IN LARGE RUMINANTS. Paravertebral anesthesia • Paravertebral anesthesia refers to the perineural injection of local anesthesia about the spinal nerves as they emerge from the vertebral canal through the intervertebral foraminae. • The technique may theoretically be carried out in any species, and at any level of the spinal cord but in practice, its main use is to provide anesthesia of the lumbar region in ruminants. • Its advantage is that it provides analgesia and muscle relaxation of the whole area covered by the segmental nerves blocked .

9. CONT... Paravertebral anesthesia is easy to carry out, and almost always effective, except in the very large beef breeds where it may be very difficult to locate the necessary landmarks. Proximal paravertebral block (Farquharson, Hall, or Cambridge Technique) • Indicated for standing laparotomy surgery such as C-section, rumenotomy, cecotomy,correction of gastrointestinal displacement, intestinal obstruction and volvulus.

10. cont... The dorsal aspect of the transverse processes of the last thoracic (T-13) and first and second lumbar (L-1 and L-2) vertebrae is the site for needle placement. • The dorsal and ventral never roots of the last thoracic (T-13) and 1st and 2nd lumbar spinal nerves emerge from the intervertebral foramina are desensitized. 10-20 ml of 2% lidocaine is injected to each site onset occurs usually within 10 minutes of injection . => Analgesia of the skin, scoliosis toward the desensitized side - due to paralysis of the paravertebral muscles, increased skin temperature due to vasodilation (paralysis of cutaneous vasomotor nerves) indicates effective block. Duration of analgesia lasts approximately 90 minutes

11. Proximal paravertebral nerve block in sheep/goat: For operations through the flank the thirteenth thoracic nerve and the first, second and third lumbar nerves are blocked . Inject 0.5 to 1.0 mL of local anaesthetic into the skin over the midpoint of each of the first, second and third lumbar processes. Wait a few minutes to allow this to take effect. The subsequent injections are made through the areas desensitized by these injections to block T13 and L1:

12. CONT... A 6 cm 19 gauge needle is adequate "Walk" the needle off the cranial and caudal edges of the transverse process of the first lumbar vertebra to block T13 and L1 respectively. This is about 2 cm deep. Inject 4-5 mL 1% lidocaine or mepivacaine to block the ventral nerve roots and 2 mL to block the dorsal nerve roots, at each site.

13. cont... To block L2 : Place a 6 cm spinal needle 2.5 to 3 cm from the midline. "Walk" the needle off the cranial edge of the transverse process of the third lumbar vertebra. Or: off the caudal edge of the transverse process of the second lumbar vertebra. Inject local anaesthetic solution below the transverse ligament to block the ventral nerve root and, as the needle is withdrawn, above it to block the dorsal nerve root. Suggested quantities of local anaesthetic are: 4 to 5 mL 1% lidocaine or mepivacaine to block the ventral nerve root and 2 mL to block the dorsal nerve root.

14. cont... To block L3 , if required. Place the needle (16 gauge 6 cm long) over the midpoint of the transverse process of the third lumbar vertebra and insert 4-5 cm deep to contact the transverse process. Withdraw slightly and direct the needle forwards to "walk" the needle off the caudal edge of the transverse process. Inject 2-3 mL of local anaesthetic solution just below the transverse proce sses. Withdraw the needle to above the transverse process and inject another 2 to 3 mL local anaesthetic.

15. cont... Alternative options : The needle may be "walked" off the cranial edges of L1, L2 and L3 to block T13, L1 and L2 respectively. Onset of analgesia may occur as soon as five minutes after injectio n the flank should be anaesthetised after about 10 minutes. Duration of analgesia is approximately one hour with plain lidocaine solution, longer if lidocaine solution with adrenaline is used.

16. Distal paravertebral nerve block in large ruminants.

17. Distal paravertebral block (Magda, Cakala, or Cornell technique) • Indicated for same as proximal paravertebral block above. • The dorsal and ventral rami of the spinal nerves T13, L1 and L2 are desensitized at the distal ends of L-1, L-2 and L-4. A 7.5-cm, 18-gauge needle is inserted ventral to the tips of the respective transverse processes in cows where approximately 10-20 ml of a 2% lidocaine solution are injected in a fan-shaped infiltration pattern . • The needle is completely withdrawn and reinserted dorsal to the transverse process, where the cutaneous branch of the dorsal rami is injected with about 5 ml of the analgesic. • The procedure is repeated for the second and fourth lumbar transverse processes. • 10-20 ml 2% lidocaine is used per site and onset and duration similar to proximal technique.

18. Distal paravertebral block in sheep/goat. Identify the distal ends of the transverse processes of lumbar vertebrae L1, L2 and L4. Clip and disinfect the skin over the ends of the transverse processe S. For each transverse process: Use about 1 to 3 mL of 2% lidocaine at each site. Using a 7.5 cm 18 gauge needle and approaching laterally, inject in a fan pattern ventral to each transverse process (L1, L2 and L4), then partially withdraw the needle and reinsert slightly dorsal and caudal to the transverse process to inject at this site. The depth to which the needle must be inserted will vary depending on the body condition of the animal.

19. Paravertebral block in horses. This block is done to enable a surgical incision in the paralumbar fossa (flank) of a standing sedated horse . . Equipment and preparation – The clipping and aseptic preparation of the flank should be extended dorsally to the midline to include the landmarks described so that the injections can be performed aseptically. Three subcutaneous skin blebs are each made with a 25 gauge ⅝ inch needle and 3 ml of local anaesthetic. Then a 7 to 8 inch spinal needle, and 120 ml of local anaesthetic solution are used for the block.

20. Technique - A paravertebral block, involves anaesthetising the dorsal and ventral branches of T18, L1 and L2 to anaesthetise the paralumbar fossa. One, although not the only, way of performing this block is to use a vertical line up from the most caudal point (curve) of the 18th (last) rib. In a 450 kg horse a 7 to 8 inch spinal needle is used through a subcutaneous bleb of local anaesthetic. The needle is inserted about 12 cm from the midline and directed ventrally until bone (transverse process of L2) is contacted. The needle i s “walked” off, by withdrawing redirecting and advancing, the caudal edge of the transverse process. 20 ml of local anaesthetic is injected just (1cm) below the transverse process

21. cont... The needle is then repositioned so that it is on the dorsal caudal edge of the bone and another 20 ml is injected. This process is repeated 5 cm and 10 cm proximally (towards the head end) to anaesthetise LI and T18. If at any stage when advancing needles you see a twitch of the flank muscles then infuse 5 ml of local anaesthetic solution at that spot in the hope that the needle is close to a branch of a nerve. If the needle penetrates the peritoneum there will be negative pressure. Keeping some local anaesthetic in the hub of the needle will indicate when the peritoneum has been punctured with disappearance of the fluid, an indication to withdraw the needle to less depth .

22. Signs of successful block : Anaesthesia of the skin; Increased skin temperature. This occurs due to hyperaemia resulting from paralysis of cutaneous vasomotor nerves; Relaxation of flank muscles; Scoliosis (curving of the spine) towards the desensitised side.

23. Advantages over L-block or line infiltration Wide uniform analgesia from the last rib to the tuber coxae and ventrally to the fold of the flank, through all layers of the abdominal wall. Faster to carry out. Significantly smaller total volume of local anaesthetic solution is required. No haematoma formation at the proposed incision site. Produces relaxation of flank muscles and decrease in intra-abdominal pressure. Intraoperative increase in the length of the laparotomy incision can be performed if required. The peritoneum is desensitised and some abdominal viscera also.

24. Disadvantages over L-block or line infiltration: This technique is technically relatively difficult particularly in fat animals. It is difficult to identify the landmarks for injections in animals which are obese or very heavily muscled. Vasodilatation may increase haemorrhage; this is considered of minor importance. Bowing of the flank may make closure of the laparotomy incision more difficult . There is a risk of penetrating the aorta or thoracic longitudinal vein on the left side of the spine or the posterior vena cava on the right side. Caudal migration of the drug to the femoral nerve may occur with resultant loss of motor control to the hind limb.

25. Inverted L block The inverted L block is a nonspecific regional block that locally blocks the tissue bordering the caudal aspect of the thirteenth rib and the ventral aspect of the transverse processes of the lumbar vertebrae. An 18-gauge 3.8-cm needle is used to inject up to a total of 100 mL of local anesthetic solution in multiple small injection sites into the tissues bordering the dorsocaudal aspect of the thirteenth rib and ventrolateral aspect of the transverse processes of the lumbar vertebrae .

26. CONT... . This creates an area of anesthesia under the inverted L block. Advantages of the inverted L block include that the block is simple to perform, it does not interfere with ambulation,and deposition of anesthetic away from the incision site minimizes incisional edema and hematoma. Disadvantages include incomplete analgesia and muscle relaxation of the deeper layers of the abdominal wall (particularly in obese animals); possible toxicity after larger doses of A nesthetic; and increased cost because of larger doses of local anesthetic .

27. Sources of reference Thurmon, Tranquilli and Benson Veterinary Anesthesia Williams and Wilkins 1996 • Hall, Clarke, and Trim Veterinary Anesthesia WB Saunders 2000 • Muir, Hubbel and Skarda A handbook Skarda R. Techniques of local analgesia in ruminants and swine. Vet Clin North Am Food Anim Pract 1986;2:621–63. [2] Edwards B. Regional anaesthesia techniques in cattle. In Pract 2001;23:142–9. [3] Skarda R. Local and regional anesthesia in ruminants and swine. Vet Clin North Am Food Anim Pract 1996;12:579–626. [4] Elmore RG. Food animal regional anesthesia, bovine blocks: cornual. Vet Med 1980;75: 1610–2. [5] Navarre C. Numbing: nose to tail. Proceedings from the 39th Annual Convention of AABP 2006;39:53–5. [6] Noordsy J, Ames N. Local and regional anesthesia. In: Noordsy J, Ames N, editors. Food animal surgery. 4th edition. Yardley (PA): Veterinary Learning Systems; 2006. p. 21–42.of Anesthesia Mosby 1999