Local Anesthesia

Question 1

what are 2 reasons we should use local anesthesia in food animals?

Answer 1

1. ruminants are poor candidates for general anesthesia
2. the cost of general anesthesia would be too much

Question 2

why are food animals poor candidates for general anesthesia?

Answer 2

Risks
- compartment syndrome
- bloat
- regurgitation
- long fasting requirements (24hr at least)

Question 3

what 2 drugs are most commonly used as local anesthetics in FA?

Answer 3

1. lidocaine hydrochloride 2%
2. bupivacaine

Question 4

what is the toxic dose for lidocaine in cattle vs small ruminants?

Answer 4

cattle = 10 mg/kg
SR = 5 mg/kg

Question 5

You can increase potency and duration of lidocaine or bupivacaine by adding what drug?

Answer 5

epinephrine

but do not use this in spinal cord or at tissue edges because it will cause necrosis.

Question 6

What is the mechanism of lidocaine as a local anesthetic?

Answer 6

blocks fast voltage-gated Na Channels in the neuronal cell membrane. The channels do not open, therefore an action potential will not be generated.

Question 7

what is the difference between local anesthesia for dehorning in cattle vs SR?

Answer 7

cattle - block cornual branch of zygomaticotemporal nerve

SR - block cornual branch of zygomaticotemporal nerve and cornual branch of infratrochlear nerve

Question 8

What are common clinical uses for inverted L, distal paravertebral, line, and proximal paravertebral blocks that anesthetize the PLF and abdominal wall?

Answer 8

c-sections
LDA, RDA
rumenotomy
exploratory
R&A for intussusception

Question 9

where is the are of anesthesia for an inverted L block?

Answer 9

behind the 13th rib and ventral to transverse processes of the lumbar vertebrae

Question 10

what size+length needle should you use for most blocks?

Answer 10

18 gauge
1.5 inch

note that this is adjusted based on BCS and site (ie. need for spinal needles)

Question 11

what are the concerns for local anesthetic blocks in animals with higher BCS?

Answer 11

that you will get incomplete anesthesia of the deeper layers. Ideally, you want to block skin, SQ, ext abdominal obl, int abdominal obl, transversus abdominus, and peritoneum.
If an animal has a higher BCS, maybe you should use a longer needle.

Question 12

what does the distal paravertebral block anesthetize?

Answer 12

dorsal and ventral rami of spinal nerves T13, L1, and L2 at the distal end of transverse processes L1, L2, and L4.

Question 13

For a inverted L block, you should use ~ _____ mL lidocaine in an adult cow.

Answer 13

150-200

Question 14

For a distal paravertebral block, you should infuse ~_____ mLs (split 10-20 mL per site) dorsal and ventral transverse processes.

Answer 14

60-120

Question 15

what is the most common use for a line block (a block that anesthetizes a specific area of the PLF)?

Answer 15

c-sections or other emergent procedures.

Question 16

why should you NOT use line blocks in fresh cows?

Answer 16

line blocks have the potential to delay healing and have hematomas or edema.
Fresh cows have impacted immune systems, so they would be at higher risk for these complications.

Question 17

what does the proximal paravertebral block anesthetize?

Answer 17

dorsal and ventral nerve roots of T13, L1, and L2 spinal nerves as they emerge from the intervertebral foramen.

Question 18

What type of needles do you need to use for a proximal paravertebral block?

Answer 18

first, you should block the skin and muscle with 18g, 1.5 inch needle

then, you can use a 14g needle to guide a 4-6 inch 18g spinal needle.

Question 19

how much lidocaine should you infuse for each site in a proximal paravertebral block?

Answer 19

6-10 mL per site

Question 20

How do you know you have successfully performed a proximal paravertebral block?

Answer 20

scoliosis

Question 21

what are the most common uses for epidural anesthesia?

Answer 21

prolapses and dystocias

Question 22

what does epidural anesthesia block? (3 things)

Answer 22

perineum
caudal vagina
rear quarters of mammary gland

Question 23

how do you perform epidural anesthesia?

Answer 23

• clip and scrub
• stand behind cow (midline)
• move tail up and down to find intervertebral space (S5-C1)
• move tail down, then place 18g 1.5 inch needle through skin
• use hang and drop technique
• one you’re in, place syringe of lidocaine on needle and infuse.

Question 24

what is the hang and drop technique?

Answer 24

When performing an epidural, you push the needle through the skin and place lidocaine in the hub of the needle.
When advancing the needle, the lidocaine will be drawn in by negative pressure when you get into the correct spot.
then you can attach your syringe and infuse anesthetic slowly.

Question 25

T/F: you should use no more than 2 mL of lidocaine for a caudal epidural

Answer 25

false – no more than 7 mL

Question 26

T/F: hang and drop technique does NOT work in small ruminants

Answer 26

true

Question 27

You can add ________ to an epidural to help with duration, but this can cause systemic affects and should not be used in pregnant animals.

Answer 27

xylazine

Question 28

What is the biggest downside to high-volume caudal epidurals (4-6 mg/kg)?

Answer 28

they will make the animal go down and itll take a few hours to stand.

Question 29

what are the indications for lumbosacral epidurals?

Answer 29

c-sections
hernias
prolapses
penile procedures
preputial procedures
procedures involving rear limbs.

Question 30

what is the injection site for a lumbosacral epidural?

Answer 30

just caudal to the last spinous process of L6

Question 31

what would be an indication for distal limb anesthesia?

Answer 31

digital sepsis

Question 32

T/F: absence of radiographic changes in cases of digital sepsis has a better prognosis and can likely be treated with antibiotics alone

Answer 32

true

if deep infection (xray changes), prompt sx treatment and Abs is recommended.

Question 33

What is the name of the procedure described below?

restrain cow and place tourniquet
clip area and clean
use digital vessels or dorsal common digital vein and inject 25-30 mL lidocaine (per foot) with an 18-20g needle. This anesthesia will last for 1-1.5 hr.

Answer 33

Bier block for distal limb anesthesia.

Question 34

what are the 2 options for local anesthesia for castration?

Answer 34

1. intratesticular
2. intraspermatic cord

2-4 mg/kg per side.

Question 35

what is the most common use of a retrobulbar eye block?

Answer 35

enucleation for cancer eye (SCC)
or trauma

Question 36

what are the steps to perform a retrobulbar block?

Answer 36

use 18g spinal needle (6 inch)
bend needle with curve of globe to pass it around the globe
use finger to deflect globe away from needle
infuse 15-20 mL lidocaine at each site (dorsal, ventral, medial, lateral)

Question 37

T/F: the Peterson eye block requires more skill but is associated with producing less edema and inflammation.

Answer 37

true

it anesthetizes CN 3, 4, 5, and 6 (everything except the eyelid)

Question 38

what are the 3 indications for local teat anesthesia?

Answer 38

teat lacerations
teat amputation
teat wart removal

Question 39

what are the 2 methods for teat anesthesia?

Answer 39

1. ring blocks – make ring around base of teat, infuse 5-10 mL lidocaine
2. V-block – for localized lesions of teat.

both require 22-25g needle.