Local Anesthesia Flashcards

1
Q

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

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

why are food animals poor candidates for general anesthesia?

A

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

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3
Q

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

A
  1. lidocaine hydrochloride 2%
  2. bupivacaine
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4
Q

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

A

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

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5
Q

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

A

epinephrine

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

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6
Q

What is the mechanism of lidocaine as a local anesthetic?

A

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

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7
Q

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

A

cattle - block cornual branch of zygomaticotemporal nerve

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

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8
Q

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

A

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

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9
Q

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

A

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

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10
Q

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

A

18 gauge
1.5 inch

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

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11
Q

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

A

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.

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12
Q

what does the distal paravertebral block anesthetize?

A

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

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13
Q

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

A

150-200

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14
Q

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

A

60-120

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15
Q

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

A

c-sections or other emergent procedures.

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16
Q

why should you NOT use line blocks in fresh cows?

A

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.

17
Q

what does the proximal paravertebral block anesthetize?

A

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

18
Q

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

A

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.

19
Q

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

A

6-10 mL per site

20
Q

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

A

scoliosis

21
Q

what are the most common uses for epidural anesthesia?

A

prolapses and dystocias

22
Q

what does epidural anesthesia block? (3 things)

A

perineum
caudal vagina
rear quarters of mammary gland

23
Q

how do you perform epidural anesthesia?

A
  • 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.
24
Q

what is the hang and drop technique?

A

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.

25
Q

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

A

false – no more than 7 mL

26
Q

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

A

true

27
Q

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

A

xylazine

28
Q

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

A

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

29
Q

what are the indications for lumbosacral epidurals?

A

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

30
Q

what is the injection site for a lumbosacral epidural?

A

just caudal to the last spinous process of L6

31
Q

what would be an indication for distal limb anesthesia?

A

digital sepsis

32
Q

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

A

true

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

33
Q

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.

A

Bier block for distal limb anesthesia.

34
Q

what are the 2 options for local anesthesia for castration?

A
  1. intratesticular
  2. intraspermatic cord

2-4 mg/kg per side.

35
Q

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

A

enucleation for cancer eye (SCC)
or trauma

36
Q

what are the steps to perform a retrobulbar block?

A

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)

37
Q

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

A

true

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

38
Q

what are the 3 indications for local teat anesthesia?

A

teat lacerations
teat amputation
teat wart removal

39
Q

what are the 2 methods for teat anesthesia?

A
  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.