Paravertebral nerve block in animals

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

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.

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.

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).

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.

• 1: PROXIMAL PARA VERTEBRAL NERVE BLOCK.
• 2:DISTAL PARA VERTEBRAL NERVE BLOCK.

• 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.

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.
• Indicated for standing laparotomy surgery such as C-
section, rumenotomy, cecotomy,correction of gastrointestinal
displacement, intestinal obstruction and volvulus.

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

• 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:

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.

cont...
:
• 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.

cont...
, 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 processes.
• Withdraw the needle to above the transverse process and
inject another 2 to 3 mL local anaesthetic.

cont...
:
• 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 injection 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.

• 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.

• 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
processeS.
• 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.

• 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.

• 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 is“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

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.

: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.

• 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.

• 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.

• 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.

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 Anesthetic; and increased cost
because of larger doses of local anesthetic.

• 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

Paravertebral nerve block in animals

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Paravertebral nerve block in animals