Local anesthesia and nerve blocks in large animals.

LOCALANESTHESIAAND NERVE
BLOCKS IN LARGE ANIMALS
Prepared by:
Ganga Prasad Yadav
MVSc
Veterinary Surgery and Radiology

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).

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.

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.

 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

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

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

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.

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.

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.

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.

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.

Pharmacokinetics
Absorption
 Drugs with greater lipid solubility and protein binding will results lower
systemic absorption.
Metabolism
 Ester linked LA are metabolised in blood by nonspecific 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.

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.

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.

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.

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.

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.

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.

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.

Levobupivacaine
Similar to bupivacaine
in properties and
clinical uses.

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%.

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.

Local anesthesia toxicity
Systemic
 CNS: Muscle twitching,
Seizure, Coma and Death
 Cardiac toxicity: CV
depression, Colapse
 Methemoglobinemia:
Benzocaine and Prilocaine

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

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

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.

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.

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

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.

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.

• Cornual nerve
block in goat:
Cornual branch of
Zygomaticotemporal
and infratrochlear
nerves are are
blocked.

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.

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.

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.

Retrobulbar anesthesia
• Indication: Enucleation of
eye ball.
• Technique:
Oriculopalpebral anesthesia
is given. A hypodermic
needle is turned/curved at
appropriate angle 15-20
degree.

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.

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.

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.

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.

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.

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.

Front limbs
Dorsal metacarpal vein
Planter metacarpal vein
Radial metacarpal vein
Rear limbs
Cranial branch of lateral
saphenous vein
Lateral planter vein

Teat/udder anesthesia/analgesia
Ring block: repair of teat laceration, teat
fistula.
Teat cistern infusion: removal of teat
polyps, teat spider.

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.

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

In fore limb, Proximal
to carpus
 Median
 Ulnar
 Musculocutaneous
In hind limb, Proximal
to tarsus
 Tibial
 Saphenous
 Superficial peroneal
 Deep peroneal

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

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

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

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.

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.

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