11. Regional Anesthesia and Epidurals

Question 1

what stage of the pain pathway does regional anesthesia block?

Answer 1

transmission

Question 2

why use regional anesthesia?

Answer 2

reduces amount of drugs needed and thus their side effects post before and after anesthesia

Question 3

topical or surface anesthesia?

Answer 3

1. larynx to avoid spasm during intubation
2. splash block (open wound, or before closing)
3. corneal (for eye exam, proparacaine, don’t use regular lidocaine, its acid)

Question 4

EMLA cream

Answer 4

• type of topical anesthetic for venipucture or small mass removal
• long onset of action, and only lasts 30 minutes

Question 5

Line block

Answer 5

• local anesthetic over incision line, some surgeons don’t like the swelling it causes
• desensitizes linea alba
• used for c-sections to avoid opiods

Question 6

local infiltration

Answer 6

infection of local anesthetic into or around planned surgical field, NOT A SPECIFIC NERVE

• line block
• intratesticular block for castration
• ring block (extremity, tail, dehorning) HUGE volume of anesthetic

Question 7

Epidural anesthesia target?

Answer 7

spinal nerves before exiting

Question 8

limits of the epidural space?

vs. spinal anesthesia?

Answer 8

• **interarcuate ligament and dura mater

vs. spinal anesthesia is in subarachnoid space (in CSF)

Question 9

lumbo sacral space used in small animals why?

Answer 9

spinal cord ends before then, no risk of hitting it, only would hit dural sac (end of subarachnoid space, its small, but possible to hit)

Question 10

landmarks for epidural?

Answer 10

1. iliac crest
2. medial sacral crest (spinal process of sacrum)
3. spinous process of L7

Question 11

You don’t feel most of the structures the epidural needle pierces (supraspinous ligament,interspinous ligament) but you can feel piercing the _______

Answer 11

interarcuate ligament (the roof of the epidural space)

some say ‘2 pops’ = interspinous and interarcuate ligaments

Question 12

tuohy needle is curved to ?

Answer 12

push the dura down instead of piercing it, can feel each tissue as you pierce it

Question 13

hanging drop technique

Answer 13

advance needle until percieved interarcuate ligament. fill hub of needle with saline. when needle enters epidural space the drop should be* aspirated!! Can be a false negative.

Question 14

Loss of resistance technique

Answer 14

• advance needle, attach syringe, apply pressure to plunger and advance needle thru interarcuate ligament.
• RESISTANCE DROPS suddenly in epidural space

Question 15

drugs in epidural?

Answer 15

1. local anesthetic
   - low concentration bupivicaine can cause sensory block without motor blockade
2. opioids
   - morphine, fentanyl
   - analgesia without motor blockade

Question 16

What amount of animal is desensitized?

Answer 16

depends on volume being injected into epidural space. more volume -> higher up towards thorax (all the way up could cause respiratory paralysis)

Question 17

advantage of peripheral nerve block?

Answer 17

small amount of anesthetic will block a huge area.

Question 18

inject anesthetic into the nerve?

Answer 18

NOOO will cause irreparable nerve damage

Question 19

techniques for peripheral nerve blocks?

Answer 19

1. blind
2. nerve stimulation (using insulated needle, based on muscular response) only works for SENSORY AND MOTOR nerves
3. ultrasound guidance

Question 20

current needed to cause muscle response?

Answer 20

0.3-0.5 mA

lower than 0.3 may mean needle is IN THE NERVE

Question 21

positive electrode is connected to the ___

Answer 21

skin of the patient

Question 22

only the _____ conducts electricity

Answer 22

tip of the needle

Question 23

when injecting anesthetic, what is special about the syringe

Answer 23

want some air in the syringe with the anesthetic. Watching the air bubble deform during injection can mean the needle is in the wrong position.

Question 24

gold standard of peripheral blocks

Answer 24

ultrasound guidance, can watch anesthetic being injected around the nerve.
can be combined with stimulation

Question 25

____ frequency transducer for ultrasound guided block

Answer 25

high, better detail

Question 26

infraorbital nerve block used for? | cautions?

Answer 26

for rhinoscopy, extracting incisor/canine, nasal surgery - inject outside foramen, can be intra or extra-orally - be careful of infraorbital artery and piercing eye in cats

Question 27

maxillary nerve block technique? used for

Answer 27

- thru infraorbital canal, thread IV catheter in canal then inject - dental procedures

Question 28

inferior alveolar/mandibular block vs. mental block

Answer 28

- entire lower jaw - palpade mandibular foramen or do extraoral by palpating foramen with finger just lower incisors

Question 29

complication with bilateral inferior alveolar block

Answer 29

spread and block lingual -> self mutilation

Question 30

intercostal block anatomy? technique? use?

Answer 30

- nerve on caudal margin of rib - blind, touch rib, then pull back more caudally, aspirate - if incising at 4th space block that rib and 2 in front and behind.

Question 31

Can you do a subarachnoid injection (spinal injection/ into CSF) at the lumbosacral space?

Answer 31

yes so be careful, especially in young animals

Question 32

Difference between spinal (subarachnoid) vs. epidural

Answer 32

- spinal injection is faster, needs less volume, very dense homogenous bilateral block, stays in CSF doesn't last as long -

Question 33

most common tissue in epidural space? | so?

Answer 33

fat | effect is not as predictable, homogenous, 'patchy'

Question 34

only in the lumbosacral space?

Answer 34

nah, can do in thoracic area to block thoracic limb nerve roots (using nerve stimulation) But be careful of the brainstem

Question 35

drugs for local anesthetics

Answer 35

- bupivicaine - .5-1 mg/kg 1-2 hours of surgery, 4-6 of analgesia - ropivacaine - less toxic, same duration, some vasoconstrictive effect - lidocaine - short acting .5-1hr

Question 36

how to know the local anesthetic epidural has spread

Answer 36

1. sympathetic trunk -> relaxation of respiratory muscles. 2. bradycardia if it hits the respiratory center that really bad

Question 37

higher concentration anesthetic of epidural

Answer 37

better block, longer lasting, faster onset

Question 38

ideal drug for epidural space? | why?

Answer 38

****morphine | low liposolubility!!!!

Question 39

drugs used in epidurals?

Answer 39

1. opioids 2. Alpha 2s (good analgesia, some local anesthetic effect, bradycardia) 3. Ketamine (short analgesia, can prolong local anesthetics, not useful alone) 4. vasoconstrictors/epinephrine (may prolong duration of action, more effective with lidocaine/drugs causing severe vasodilation)