11. Regional Anesthesia and Epidurals Flashcards
what stage of the pain pathway does regional anesthesia block?
transmission
why use regional anesthesia?
reduces amount of drugs needed and thus their side effects post before and after anesthesia
topical or surface anesthesia?
- larynx to avoid spasm during intubation
- splash block (open wound, or before closing)
- corneal (for eye exam, proparacaine, don’t use regular lidocaine, its acid)
EMLA cream
- type of topical anesthetic for venipucture or small mass removal
- long onset of action, and only lasts 30 minutes
Line block
- local anesthetic over incision line, some surgeons don’t like the swelling it causes
- desensitizes linea alba
- used for c-sections to avoid opiods
local infiltration
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
Epidural anesthesia target?
spinal nerves before exiting
limits of the epidural space?
vs. spinal anesthesia?
- **interarcuate ligament and dura mater
vs. spinal anesthesia is in subarachnoid space (in CSF)
lumbo sacral space used in small animals why?
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)
landmarks for epidural?
- iliac crest
- medial sacral crest (spinal process of sacrum)
- spinous process of L7
You don’t feel most of the structures the epidural needle pierces (supraspinous ligament,interspinous ligament) but you can feel piercing the _______
interarcuate ligament (the roof of the epidural space)
some say ‘2 pops’ = interspinous and interarcuate ligaments
tuohy needle is curved to ?
push the dura down instead of piercing it, can feel each tissue as you pierce it
hanging drop technique
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.
Loss of resistance technique
- advance needle, attach syringe, apply pressure to plunger and advance needle thru interarcuate ligament.
- RESISTANCE DROPS suddenly in epidural space
drugs in epidural?
- local anesthetic
- low concentration bupivicaine can cause sensory block without motor blockade - opioids
- morphine, fentanyl
- analgesia without motor blockade
What amount of animal is desensitized?
depends on volume being injected into epidural space. more volume -> higher up towards thorax (all the way up could cause respiratory paralysis)
advantage of peripheral nerve block?
small amount of anesthetic will block a huge area.
inject anesthetic into the nerve?
NOOO will cause irreparable nerve damage
techniques for peripheral nerve blocks?
- blind
- nerve stimulation (using insulated needle, based on muscular response) only works for SENSORY AND MOTOR nerves
- ultrasound guidance
current needed to cause muscle response?
0.3-0.5 mA
lower than 0.3 may mean needle is IN THE NERVE
positive electrode is connected to the ___
skin of the patient
only the _____ conducts electricity
tip of the needle
when injecting anesthetic, what is special about the syringe
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.
gold standard of peripheral blocks
ultrasound guidance, can watch anesthetic being injected around the nerve.
can be combined with stimulation
____ frequency transducer for ultrasound guided block
high, better detail
infraorbital nerve block used for?
cautions?
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
maxillary nerve block
technique?
used for
- thru infraorbital canal, thread IV catheter in canal then inject
- dental procedures
inferior alveolar/mandibular block
vs. mental block
- entire lower jaw
- palpade mandibular foramen or do extraoral by palpating foramen with finger
just lower incisors
complication with bilateral inferior alveolar block
spread and block lingual -> self mutilation
intercostal block
anatomy?
technique?
use?
- 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.
Can you do a subarachnoid injection (spinal injection/ into CSF) at the lumbosacral space?
yes so be careful, especially in young animals
Difference between spinal (subarachnoid) vs. epidural
- ## spinal injection is faster, needs less volume, very dense homogenous bilateral block, stays in CSF doesn’t last as long
most common tissue in epidural space?
so?
fat
effect is not as predictable, homogenous, ‘patchy’
only in the lumbosacral space?
nah, can do in thoracic area to block thoracic limb nerve roots (using nerve stimulation) But be careful of the brainstem
drugs for local anesthetics
- 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
how to know the local anesthetic epidural has spread
- sympathetic trunk -> relaxation of respiratory muscles.
- bradycardia
if it hits the respiratory center that really bad
higher concentration anesthetic of epidural
better block, longer lasting, faster onset
ideal drug for epidural space?
why?
**morphine
low liposolubility!!!!
drugs used in epidurals?
- opioids
- Alpha 2s (good analgesia, some local anesthetic effect, bradycardia)
- Ketamine (short analgesia, can prolong local anesthetics, not useful alone)
- vasoconstrictors/epinephrine (may prolong duration of action, more effective with lidocaine/drugs causing severe vasodilation)
