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Local anesthesia and nerve blocks in large animals.

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Local anesthesia and nerve blocks in large animals.

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Local anesthesia and nerve blocks in large animals.

  1. 1. LOCALANESTHESIAAND NERVE BLOCKS IN LARGE ANIMALS Prepared by: Ganga Prasad Yadav MVSc Veterinary Surgery and Radiology
  2. 2. Local anesthesia Definition: defined as the reversible loss of sensation in a limited area of body without loss of consciousness by the use of a chemical agent. Also called local analgesia because local anesthesia blocks the pain transmission. It produces desensitization and analgesia of skin surfaces(topical anesthesia), tissues (infiltration and field blocks) and regional structures (conduction anesthesia, intravenous regional anesthesia).
  3. 3. Reasons for producing local anesthesia  To provide effective preemptive and multimodal analgesia.  To reduce the amount of inhalant or injectable drugs needed to maintain anesthesia.  To decrease the stress response to surgical trauma.  To reduce the potential for the development of central sensitization.
  4. 4. General considerations for local anesthesia 1.Use of sterile solutions, equipments and techniques. 2.Avoid injection into inflamed area (if possible). 3.Use a small gauze of needle as practical. 4.Aspirate for blood before injecting. 5.Use lowest effective concentration of local anesthetic drug to produce the desired effect. 6.Wait for onset of analgesia before proceeding.
  5. 5.  Non-irritating to tissues.  Reversible loss of sensation. Good penetrating qualities into body tissues. No structural damage to nerve or other tissues. Slow and gradual absorption. High potency so that low concentration can be used. No systemic adverse or side effect.  Rapid but desirable duration of action (short or long). Should not cause hyperesthesia after recovery. Near neutrality pH. Should be sterilisable. Desirable characters of local anesthesia
  6. 6. Advantages and disadvantages Advantages Suitable for performing surgery on standing animals Simple and requires no expensive or complicated equipments Performed by the surgeon himself so no need for anesthesiologist Low cost Low cardiovascular toxicity Minimal patient recovery time Used in conjunction with GA
  7. 7. Advantages and disadvantages Advantages Suitable for performing surgery on standing animals Simple and requires no expensive or complicated equipments Performed by the surgeon himself so no need for anesthesiologist Low cost Low cardiovascular toxicity Minimal patient recovery time Used in conjunction with GA Disadvantages Requires cooperative patient with or without significant restraint May require sedation Some local anesthetics are irritant or toxic to tissues
  8. 8. Classification A. On the basis of chemical structures; classified into 3 groups. 1. Ester local anesthetics: Derived from benzoic acid. Examples: Procaine, Chloroprocaine, benzocaine, amethocaine, cocaine etc. 2. Amide local anesthetics: Derived from aniline. Example: Lignocaine, Bupivacaine, Mepivacaine, Etidocaine, and Ropivacaine. 3. Ether or Ketone local anesthetics Examples: Pramoxine and dyclonine.
  9. 9. Classification A. On the basis of chemical structures; classified into 3 groups. 1. Ester local anesthetics: Derived from benzoic acid. Examples: Procaine, Chloroprocaine, benzocaine, amethocaine, cocaine etc. 2. Amide local anesthetics: Derived from aniline. Example: Lignocaine, Bupivacaine, Mepivacaine, Etidocaine, and Ropivacaine. 3. Ether or Ketone local anesthetics Examples: Pramoxine and dyclonine. B. Based on potency and duration i. Low potency and short duration eg: procaine, chloroprocaine. ii. Intemediate potency and medium duration eg: Mepivacaine, prilocaine and Lidocaine. iii. High potency and long duration eg: Tetracaine, Bupivacaine and Etidocaine.
  10. 10. Mechanism of action • LAs block nerve conduction by inhibiting influx of Na+ ions through ion-selective sodium channels in nerve membrane leading to impairment of the generation of action potential. • Thus, conduction of nerve impulses stoppage.
  11. 11. Additives 1. Epinephrine  Used as adjunct to local anesthesia.  Vasoconstriction – decrease systemic absorption of the local anesthetic agent- decrease the dose of local anesthetic required and prolongs its duration of effect.  Other vasocontrictors are: Phenylephrine or methoxamine. 2.Hyaluronidase: Used to improve the penetration and thereby shorten the onset of action and increase the spread of block.
  12. 12. Factors affecting activity and potency  Lipid solubility Increased drug lipid solubility tends to slow the rate of onset of action, increase the duration of action, and increase potency.  Protein binding Increased plasma protein binding tends to be associated with increased duration of action.
  13. 13. Pharmacokinetics Absorption  Drugs with greater lipid solubility and protein binding will results lower systemic absorption. Metabolism  Ester linked LA are metabolised in blood by non- specific plasma pesudocholinesterage.  Esterase present in liver, RBCs and synovial fluid also contribute to clearance of these drug.  Amide linked LA are almost exclusively metabolized in liver by microsomal enzyme (cyp-450). Excretion  LA are poorly water soluble which limits the renal excretion of unchanged drug.  Metabolites of -- ester linked local anesthetics are excreted in urine. -- amide linked local anesthetics are excreted in urine or bile.
  14. 14. Local anesthetics used in veterinary practices Procaine  Quick onset of action and short duration of effect (30-60 min).  Epinephrine may be added to prolonged its duration of action.  Systemic toxicity is minimal, but it occasionally causes allergic reaction due to a hydrolysis metabolite (PABA).  Used for infiltration and nerve blocks at concentration of 1-2%.  IV procaine is a CNS stimulant in horses, due to CNS stimulant and analgesic effect, illegally used in race horses.  Also added to drug formulation to prolong duration of effect. Example procaine penicillin. Cocaine The original LA isolated from leaves of coca. The only one that cause vasoconstriction.
  15. 15. Benzocaine Fast acting (approx. 30 sec) and short duration of effect (approx 30-60 min). Used exclusively for topical anesthesia. Also used as anesthetic for fish when added to water. Causes Methemoglobinemia in several species of animals so no longer in clinical practice.
  16. 16. Chloroprocaine • Similar to procaine with fast onset of action and short duration of effect(30-60)min. • Available in concentration of 1% to 3%. • Used for local infiltration blocks when a short duration effect is required. • Not widely used in veterinary medicine.
  17. 17. Chloroprocaine • Similar to procaine with fast onset of action and short duration of effect(30-60)min. • Available in concentration of 1% to 3%. • Used for local infiltration blocks when a short duration effect is required. • Not widely used in veterinary medicine. Tetracaine Also known as amethocaine. Well absorbed by surfaces. Relatively toxic. Rarely used in veterinary medicine.
  18. 18. Lidocaine  Most widely used in veterinary medicine due to fast onset of action, moderate duration of effect (1 hr ) and not decomposed by boiling, acids, or alkali.  Available as 0.5%, 1%, 1.5%, 2% and 4% solution.  Antiarrhythmic effect.  Used for infiltration anesthesia, peripheral nerve block, epidural and intrathecal block and intravenous regional anesthesia.  When administered intravenously, reduces the doses of inhalent anesthetics.  Several non-anesthetic uses when administered intravenously  as antiarrhythmic drug  as analgesics  as intestinal motility inhancer in case of ileus.
  19. 19. Mepivacaine  Similar to lidocaine with a slightly longer duration of action (upto 2 hrs) because of less intrinsic vasodilatory properties.  Available at concentrations from 0.5% to 2%.  Use in clinical practice similar to lidocaine except that it is not routinely used for intravenous regional anesthesia or for obstetric procedures because its metabolism is very slow in fetus and newborn.  Not as effective topical anesthesia as lidocaine.  Preferred agent for diagnostic peripheral nerve blocks in horse because of its lower neurotoxicity compared with other local anesthetics.
  20. 20. Bupivacaine • Highly lipophilic agent, about four times as potent as lidocaine, and with slow onset of action (20-30) min and long duration of action (3-10) hrs. • Available in concentration of 0.125 % to 0.75%. • Uses: infiltration, peripheral nerve block, epidural and intrathecal block. • Not used for topical anesthesia and not recommended for intravenous regional anesthesia due to CNS and cardio-toxicity potential.
  21. 21. Levobupivacaine Similar to bupivacaine in properties and clinical uses.
  22. 22. Levobupivacaine Similar to bupivacaine in properties and clinical uses. Ropivacaine Structurally related to mepivacaine and bupivacaine. Slightly less potent than bupivacaine. Available in concentrations of up to 1%.
  23. 23. Proparacaine Used to anesthesize the cornea of eye. Rapid onset of action (within 1 minute) and lasts for about 15-30 minutes. Non-irritant and does not affect the size of pupil. Available as 0.5% opthalmic solution. Prolonged use may produce permanent corneal opacification with accompanying visual loss.
  24. 24. Local anesthesia toxicity Systemic  CNS: Muscle twitching, Seizure, Coma and Death  Cardiac toxicity: CV depression, Colapse  Methemoglobinemia: Benzocaine and Prilocaine
  25. 25. Local anesthesia toxicity Systemic  CNS: Muscle twitching, Seizure, Coma and Death  Cardiac toxicity: CV depression, Colapse  Methemoglobinemia: Benzocaine and Prilocaine Localized Allergic reaction: Wheel, Swelling, redness
  26. 26. COMMON METHODS OF PRODUCING LOCALANESTHESIA 1. Surface (topical) anesthesia 2. Intrasynovial anesthesia 3. Infiltration anesthesia 4. Spinal anesthesia 5. Intravenous regional local anesthesia 6. Regional anesthesia
  27. 27. Surface (Topical) anesthesia • Refers to use of local anesthetics in solution, sprays as well as in various creams and ointments on mucous membranes; drops into the eye, sprays or brush in laryngeal area, infuse into nostrils, urethra or rectum.
  28. 28. Intrasynovial anesthesia • Used in joints, bursa and tendon sheaths. • Useful for both diagnosis of lameness and for general pain relief. • As these sites are prone to infection, used in sterility condition.
  29. 29. Infiltration anesthesia  Nerve endings are blocked at the actual site of the operation. Field anesthesia Linear infiltration Inverted “L” or “7” block Ring block  Uses To minimize or prevent pain To facilitate surgery  Skin incision  Surgical removal of superficial tumors  Wound repair
  30. 30. Spinal anesthesia  Injection of local anesthetic around the spinal cord.  Lidocaine, bupivacaine or morphine used.  All the segmental nerves ( sensory and motor) nerves which pass through the anesthetic are paralysed, although when opioid used, only sensory nerves blocked. Two types 1. Epidural or extradural anesthesia: local anesthetic deposited into extradural space. 2. True spinal anesthesia: local anesthesia deposited into subarachnoid space.
  31. 31. Nerve blocks Nerve blocks of head 1. Cornual nerve block • Indication: Dehorning, Disbudding, Horn injury • Anatomy: Branch of lacrimal nerve(also called zygomaticotemporal), which is a branch of opthalmic division of trigeminal nerve is blocked. • Injection site: Upper third of temporal ridge about 2.5 cm below the base of horn.
  32. 32. • Cornual nerve block in goat: Cornual branch of Zygomaticotemporal and infratrochlear nerves are are blocked.
  33. 33. Auriculopalpebral nerve block • Indication: to prevent eyelid closure during examination of eyeball. • Injection site: needle is inserted in front of the base of the ear at the end of zygomatic arch and is introduced until its point lies at the dorsal border of the arch. • Caution: does not provide analgesia of the eye or eyelids. • Nerve blocks in horse: less commonly used but mainly used general anesthesia.
  34. 34. Infraorbital and maxillary nerve block, Mental and Mandibular nerve block • Infraorbital nerve block: done at the exit of infraorbital nerve from infraorbital foramen. • Desensitize upper lip, nose and skin supplied by nerve. • Maxillary nerve block is achieved by inserting needle into maxillary canal and anesthetic deposited in canal. • Desensitizes teeth as far as first molar, maxillary sinus and skin upto medial canthus of eye. • Mental nerve block: done at the exit of mental nerve from mental foramen. • Desensitizes lower lip.
  35. 35. Mandibular Nerve Block  Achieved by inserting needle in the mandibular canal.  Desensitizes lower incisors and premolars. Peterson Nerve Block Indication: Enucleation of eye ball and eyelid. Technique: Notch formed by supraorbital process cranially, zygomatic arch ventrally and coronoid process of mandible caudally.
  36. 36. Retrobulbar anesthesia • Indication: Enucleation of eye ball. • Technique: Oriculopalpebral anesthesia is given. A hypodermic needle is turned/curved at appropriate angle 15-20 degree.
  37. 37. Anesthesia of flank region Most commonly used in cattle . Rarely used in horses. Indications: GIT surgery(right/left flank) eg: Rumenotomy, intestinal surgery, cesarean section, urinary bladder surgery etc.
  38. 38. Linear infiltration Indication : Standing laprotomy, surgery such as C-section, rumenotomy. Cecotomy, correction of GI displacement, intestinal obstruction and volvulus. • Anatomy and injection site: multiple subcutaneous injections of 0.5 – 1 ml of 2% lidocaine solution, 1-2 cm apart along the incision line.
  39. 39. Inverted L or 7 block  Indication : Standing laprotomy, surgery such as C-section, rumenotomy. Cecotomy, correction of GI displacement, intestinal obstruction and volvulus.  Anatomy and injection site: this is a nonspecific regional analgesic technique in which all the nerves entering surgical field are desensitized.
  40. 40. Proximal paravertebral nerve block • Also called Farquharson, Hall or Cambridge technique. • Indication : Standing laprotomy, surgery such as C-section, Rumenotomy. Cecotomy, correction of GI displacement, intestinal obstruction and volvulus. • Anatomy and injection site: Dorsal aspect of transverse processs of the last thoracic (T13) and First and second lumbar (L1 and L2) vertebrae is the site for needle placement. • The dorsal and ventral nerve roots of the last thoracic and first and second lumbar spinal nerves emerge from the intervertebral foramina are desensitized.
  41. 41. Distal paravertebral nerve block • Also called Magda, Cakala or Cornell technique. • Indication : Standing laprotomy, surgery such as C-section, Rumenotomy. Cecotomy, correction of GI displacement, intestinal obstruction and volvulus. • Anatomy and injection site: The dorsal and ventral rami of spinal nerves T13, L1 and L2 are desensitized at the distal ends of L1, L2 and L4.
  42. 42. Intravenous regional Analgesia of limb • Also called Biers block. • Indication: amputation of digits, removal of interdigital hyperplastic lesions, treatment of infections of foot. • Anatomy and injection site: injecting local analgesic into any accessible superficial vein in the extremity isolated from the general circulation by a tourniquet, an elastic bandage or an inflatable cuff. • The limb distal to site of application of the tourniquet becomes analgesic and remains so until tourniquet is released.
  43. 43. Front limbs Dorsal metacarpal vein Planter metacarpal vein Radial metacarpal vein Rear limbs Cranial branch of lateral saphenous vein Lateral planter vein
  44. 44. Teat/udder anesthesia/analgesia Ring block: repair of teat laceration, teat fistula. Teat cistern infusion: removal of teat polyps, teat spider.
  45. 45. Intra-testicular anesthesia/analgesia • Indication: surgical castration in cattle. • 8-10 ml local anesthetic is injected into each testicle. • In horse, local anesthetic can be injected in conjuction with general anesthesia. Internal pudendal nerve block Indication: surgical examination of penis. Site: ischio-rectal fossa.
  46. 46. Regional anesthesia of Nerve blocks in Limbs  Used in for diagnosis of lameness.  Nerve blocks carried out from bottom to top.  Sequences of blocks up to knee/hock  Digital palmar/plantar nerve block  Abaxial nerve block  Low four point nerve block  High four point nerve block
  47. 47. In fore limb, Proximal to carpus  Median  Ulnar  Musculocutaneous In hind limb, Proximal to tarsus  Tibial  Saphenous  Superficial peroneal  Deep peroneal
  48. 48. Palmar / Plantar Digital Nerve Block • Volume: – 1 – 2 cc • Needle: – 25 gauge, ¾ inch • Technique: – Palpate the lateral and the medial palmar/plantar digital neurovascular bundle. – Place needle axial to the collateral cartilage, as low in the foot as possible. – Can perform with the limb held up or with the horse standing on the limb. • Blocks palmar/plantar third of foot and sole – Navicular bone – Navicular bursa – Digital cushion – Distal aspect of DDFT – Sole, bars, heels, frog – (occasionally) coffin joint
  49. 49. Abaxial Nerve Block • Volume: – 1 – 2 cc • Needle: – 25 gauge, ¾ inch • Technique: – Palpate the lateral and medial palmar/plantar digital neurovascular bundle on the abaxial aspect of the sesamoid bones. – Insert needle along length of the nerve. – Nerve is at the palmar/plantar aspect of the bundle • Blocks everything below the level of the fetlock – Foot – Coffin joint – Pastern Joint – Distal DDFT – Distal Extensor Tendons – Distal Sesamoidean Ligaments
  50. 50. Low Four Point Nerve Block • This block is specific for the forelimbs • Volume & Needle: – 2 – 3cc – 1 inch, 22 gauge • Technique: – Lateral & medial palmar nerves (2) – Lateral & medial palmar metacarpal nerves (2) – Lateral & medial palmar nerves • Between the DDFT and suspensory ligament, halfway up the length of the cannon bone • Avoid the flexor tendon sheath – Lateral & medial palmar metacarpal • Distal to the ‘button’ of the lateral & medial splint bone
  51. 51. HIGH FOUR POINT NERVE BLOCK • Performed when low four point nerve block fails. • 3-5 ml local anesthetic deposited using 25G 5/8’ needle, is inserted through the fascia near the nerve at dorsal border of deep digital flexor tendon. • Used to examine the lameness.
  52. 52. References 1. Veterinary Anesthesia and Analgesia, the 5th edition of Lumb and Jones. 2. Hand book of Veterinary anesthesia, 5th edition by William W. Muir, III, John A.E. Hubbell, Richard M. Bednarski and Phillip Lerche. 3. Anesthesia and Analgesia for Veterinary Technicians, 4th edition by John A. Thomas and Phillip Lerche. 4. Essentials of Veterinary Pharmacology and Therapeutics by Harpal Singh Sandhu and Satyavan Rampal. 5. A hand book on Veterinary Local Anesthesia by Syed Sajjad Hussain.

Editor's Notes

  • Also, due to decreased systemic absorption, decreased probability of systemic toxicity.
  • Drugs having higher lipid solubility and protein binding result lower systemic absorption.
  • Rarely used for topical anesthesia due to not very effective via this route.
  • Tetracaine well absorbed by surfaces and is used on mucous membrane.
  • Preffered for peripheral nerve block due to Lower neurotoxicity compared to other anesthetics
  • These are newer long acting LA with less cardiotoxicity but more expensive.
  • Lidocaine is used to desensitize larynx and to prevent laryngospasm
  • Note: In adult cattle with well developed horns, a ring block around the base of horn may also done for better work.
  • block ideally desensitises cranial nerves II,
    III, IV, VI and the ophthalmic and maxillary branches of V; and
    therefore all the extraocular muscles, the entire globe and the
    conjunctivae
  • ×