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Special Topics in Equine Clinical Practice > Local Anesthesia > Flashcards

Local Anesthesia Flashcards

1
Q

what are the benefits of local and regional anesthesia? (3)

A
  1. allow examination and procedures without general anesthesia (bypass risks assoc with induction and recovery)
  2. provide analgesia without systemic side effects
  3. can balance analgesia by being combined with sedation
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2
Q

what is the most common drug used for local anesthesia?
what is the onset and duration of this drug?

A

2% lidocaine

onset = 3-5 min
duration = 1-2 hr
cheap

mepivacaine and bupivicaine are also available.

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3
Q

T/F: IV lidocaine can delay recovery

A

true

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4
Q

when should you perform intratesticular block with lidocaine?

A

at your first scrub in order to give it enough time to work prior to cutting.

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5
Q

When you need to provide local anesthesia to the eye, what topical drug can you use?

A

proparacaine

onset is 15 seconds
and duration is 15-30 min

note that sedation AND local anesthesia is required for examination, diagnostics, and minor surgical procedures.

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6
Q

which block is the MOST important motor block of the eye?

A

auriculopalpebral

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7
Q

what size needle and how many mL of anesthetic should be administered with an auriculopalpebral block?

A

25g 1” needle
1-2 mL

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8
Q

which block would desensitize the sensory component of the upper eyelid?

A

supraorbital

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9
Q

Which block would desensitize the sensory component of the temporal/lateral canthus as well as 25% of the upper lid?

A

lacrimal

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10
Q

which block would desensitize the nasal canthus?

A

infratrochlear

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11
Q

which block would desensitize the temporal 75% of the lower lid?

A

zygomaticofacial

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12
Q

Which block provides analgesia to the upper lip and nose?

A

infraorbital I

inject it over the infraorbital foramen (in between the nasal notch and facial crest)

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13
Q

how many mL of local anesthetic should you use for an infraorbital I block?

A

4-5 mL

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14
Q

What structures does the infraorbital II block desensitize (note: this is the block in which the needle is threaded into the infraorbital foramen)?

A
  • teeth to 1st molar
  • maxillary sinus
  • roof of nasal cavity
  • skin to medial canthus
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15
Q

What structures are desensitized using a maxillary block?

A

all upper teeth, sinuses, and the nasal cavity.

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16
Q

Where should the maxillary block be administered and how many mLs of anesthetic should be used?

A

insert a 3.5” needle 90 degrees just ventral to the zygomatic process near the caudal 1/3 of the eye.

insert 15-20 mL

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17
Q

The mandibular block desensitizes all mandibular structures, the lateral canthus, and the mandibular cheek teeth. What size needle should you use and how many mL should you administer?

A

20g, 6” needle
infuse 15-20 mL

18
Q

If you wanted to achieve analgesia of the lower lip, what block would you use?

A

mental I

I’d inject 5 mL over the mental foramen (palpated by pushing tendon of depressor labi inferioris)

19
Q

How is the mental II block different from mental I?

A

mental II block provides analgesia to the lower incisors and caudal to the 3rd premolar. this is because the needle is threaded into the foramen.

Whereas the mental I only provides analgesia to the lower lip and the needle is not threaded.

20
Q

what are some indications to perform an epidural?

A
  • performing any procedure involving rectum, vagina, perineum, urethra, and bladder
  • doing obstetrical manipulations
  • provide analgesia of stifles and hocks
21
Q

what are some contraindications to performing an epidural?

A
  • infection at the puncture site
  • systemically septic
  • uncorrected hypovolemia
  • on anticoagulant Rx
  • have anatomic abnormalities
22
Q

where is the epidural space located?

A

within the spinal canal
outside of the dura mater and subarachnoid space.

23
Q

why is a caudal epidural preferred over lumbosacral in horses?

A

with lumbosacral epidurals, it is easier to hit the subarachnoid space than the epidural space resulting in dural puncture and CSF tap, it requires special equipment, and there is higher risk of motor blockade and ataxia.

but the caudal epidural is simple and requires no special equipment. the caudal epidural most importantly preserve locomotor function of the hindlimbs.

24
Q

what are the landmarks for the lumbosacral epidural/subarachnoid?

A

1-2 cm caudal to a line drawn from the cranial edge of tuber sacrale and dorsal midline.

25
Q

what is the landmark for a caudal epidural?

A

palpate Co1-Co2 as the first midline depression caudal to the sacrum
(itll be the first movable coccygeal articulation when the tail is raised and lowered)

26
Q

what are the 2 caudal epidural techniques and how do they differ?

A

technique 1: 18g, 1.5” needle entered into space between co1-co2 perpendicular to the skin

technique 18g, 2:5-7.5” needle inserted at the caudal part of the space between co1-co2 and inserted at a 30 degree angle (better for horses who have had multiple epidurals)

27
Q

when should you use a catheter instead of a needle for an epidural?

A

when there will be repeated or long-term use.

needles are used for one time administrations.

28
Q

describe the hanging drop technique

A

when you get the needle into the epidural space, place a drop of saline into the hub and if the saline gets sucked into the needle, you’ll know youre in the epidural space.
this was due to the negative pressure of the epidural space.

29
Q

describe the “loss of resistance” epidural technique

A

fill syringe with saline and an air bubble.
once you think you are in the epidural space, attempt to inject the saline.
if the air bubble does not compress, you are in the correct epidural space.
if you are not in the epidural space, the air bubble will smaller and the plunger may “bounce back”.

30
Q

when are epidural catheters indicated?

A

when continuous epidural analgesia is used.
for example, pelvic fractures, hindlimb fractures, septic joints, and other very painful things.

31
Q

T/F: epidural catheters can cause localized inflammation and fibrosis

A

true

32
Q

what classes/types of drugs can be used for epidurals?

A
  • local anesthetics
  • alpha-2 agonists
  • opioids
  • ketamine
33
Q

T/F: using alpha-2 agonists in an epidural can cause systemic effects as well as local.

A

true

this block is ideal though because when combined with local anesthetics, it acts synergistically to prolong analgesia.

34
Q

which of the alpha-2 agonists has a longer duration for epidural use – xylazine or detomidine?

A

xylazine

note detomidine also have more systemic side effects.

35
Q

Why are opioids a great option for epidurals?

A

they inhibit pain transmission in the dorsal horn of the spinal cord while …
- provide analgesia without motor nerve blockade
- having minimal dose requirements
- having few side effects.

36
Q

T/F: morphine is the most effective opioid to use for epidurals

A

true
its a pure mu agonist with a slow onset (1-5 hr), but long duration (6-16 hr)

37
Q

why would regular morphine used in epidurals for horses as opposed to preservative-free?

A

regular morphine is more concentrated (15 mg/mL) meaning a smaller volume is used which is less expensive than preservative-free.

if you were doing repeated administration, preservative-free may be a better option.

38
Q

T/F: ketamine epidurals have good somatic but poor visceral analgesia.

A

true
to fix this, you can add a local anesthetic to improve the visceral analgesia.

39
Q

T/F: subarachnoid injection between T18-L1 with ketamine permits abdominal surgery in standing horses.

A

true

40
Q

why would you combine drugs for local anesthetics and epidurals?

A

they can act synergistically and PROLONG analgesia
they may provide BETTER analgesia than one agent alone
this MINIMIZES side effects of individual agents.

41
Q

what are complications of epidurals?

A
  • failure to achieve analgesia
  • hypoventilation
  • bradycardia
  • pruritus
  • upward fixation of patella
  • sepsis
  • recumbency
42
Q

what are a few common drug combinations for local anesthesia and epidurals?

A
  • opioids + alpha-2s
  • local + alpha-2s (dec dose of local by 30% to reduce ataxia, good for standing surgery)
  • opioid + local

Special Topics in Equine Clinical Practice (18 decks)

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