Locoregional Analgesia Flashcards
What are 3 examples of locoregional blocks?
- placement or deposition of substances near nerves, nerve roots, ganglia, or spinal cord segments
- placement of substances within affected joints
- placement of substances near or around affected structures, like tendons, bursa, or trigger points
What are some reasons that more veterinarians do not utilize locoregional anesthesia? What are 3 common adverse effects?
- time to learn and perform
- invasiveness
- cost
- urinary retention
- impaired motor function
- hair regrowth issues
What are the 3 most common means of providing local blocks and epidurals?
- blind technique - use anatomical landmarks
- neurostimulation block - microcurrent and motor response
- echo or ultrasound
What operative and post-operative benefits are associated with the use of locoregional blocks? What is an additional use for it?
OP - reduced MAC, reduced anesthesia need, analgesia
POST-OP - ambulation, appetite, reduced operative pain
chronic pain reduction
What potential toxicity occurs first with the use of locoregional blocks? What are some signs?
CNS
- dizziness
- tinnitus
- disorientation
- seizures
What potential toxicity occurs after CNS toxity associated with locoregional blocks? What medication most likely causes this? What are some signs?
cardiovascular
bupivicaine > lidocaine
- hypertension
- tachycardia
- hypotension
- prolonged PR interval
- QRS widened
What are the 2 steps of nerve transmission? What does this depend on?
- depolarization - influx of Na ions through large channels
- repolarization - outflux of K ions through channels
impulse transmission depends on gradients
What are the 2 types of nerve fibers that local anesthetics affect?
- small (A delta, B, C) - outermost autonomic and sensory nerve
- larger, myelinated (A gamma, beta, alpha) - motor fibers
sensory blocked before motor!
How does the affect on nerves differ in the different types of local anesthetics?
selectively block sensory vs. motor function - Bupivacaine, Ropivacaine
relatively non-specific - Lidocaine
What are 9 agents used in local and regional blocks?
- local anesthetics - Lidocaine, Bupivacaine, Ropivacaine
- saline
- bicarbonate
- epinephrine
- NSAIDs
- steroids
- alpha agonists
- ketamine
- narcotics
What is the onset and duration of Lidocaine like? What causes toxicity?
10-15 mins, lasts 60-120 mins
IV uptake —> dependent on cardiac, CNS, and hepatic function
What is the onset and duration of Bupivacaine like? What are 2 major differences compared to Lidocaine?
20-30 mins, lasts 4-6 hrs
- selective sensory blockade - motor sparing!
- very cardiotoxic with IV uptake
What are 4 major reasons to add slaine to local anesthetics?
- decreases pain of administration
- helps with spread and increases chance of nerve contact in blind techniques without increasing dose
- decreases chance of toxicity
- increases chances of full coverage, especially for plexus, facial, or compartmental blocks
What are 3 problems with adding epinephrine to local anesthetics?
- vasoconstriction can be detrimental - careful with peripheral digital blocks and in skin flaps!
- acidic - slows onset
- uptake near vascular bed can cause cardiac dysrhythmias and respiratory issues
In what 2 ways does bicarbonate hasten the onset of a blockade? When is it particularly used?
- raises pH, promoting a more permeable form of anesthetic
- improves intracellular binding of the drug
most important in acidic environments, like abscesses and infections
How does the location of surgery, diameter of nerve, and doses of drugs affect dosing of local anesthetics?
further caudal and distal in the animal = less total volume needed
smaller nerve = lower volume needed
higher dose = more analgesia, but more side effects
(opioid = urinary retention!)
How are sites prepared for performing locoregional blocks?
- surgical clip wide with a 40 blade
- clean scrub followed by surgical scrub
- sterile gloves, one hand = very sterile
- have vials, syringes, and needles prepared
How can intraneural injection of epidurals be avoided?
if there is pressure on injection, you are in the nerve —> pull back
What are 2 major reasons to use a reduced volume of local anesthetics in epidurals?
- decreases possibility of toxicity
- decreases chance of intraneural injection
How are nerve stimulators used?
- locator finds the nerve or plexus
- local blockade is delivered
- catheter is introduced to allow continued blockade
How is echolocation used to find nerves and plexi? How can it be used to avoid vascular injections? What limitation is associated?
high-frequency transducers of ultrasounds are used to locate the nerve based on sound waves
color doppler and compound imaging
beam penetration is limited to 5-7 cm
How are locoregional block needles placed? What should be done in blocks near the chest?
- short, deep angle bevel to reduce nerve puncture
- slow and steady advancement
attach syringe to the needle to create a closed system - brachial plexus, thoracic paravertebral
What are 3 purposes to utilize facial and dental blocks?
- reduce pain during and after dental procedures, oral and facial surgeries, and nasal desensitization during rhinoscopy or nasal biopsy
- reduce MAC
- relieve chronic pain
What nerve is responsible for sensory innervation for dental procedures? What are the 4 most common blockades?
trigeminal nerve (CN V) - ophthalmic, maxillary, and mandibular divisions
- maxillary
- mandibular
- infraorbital
- mental
What does the maxillary nerve block do? What are the 2 approaches?
desensitizes entire maxillary arcade on that side
- external face ventral to the rostral most aspect of zygomatic arch at a 90 degree angle
- oral cavity caudomedial to the last molar through the soft palate toward the ceiling
What caution needs to be taken with maxillary nerve blocks?
transient unilateral vision loss following inadvertent intravitreal injection of Bupivacaine
Where is the cranial approach to infraorbital nerve blocks? What 2 structures are desensitized?
cranial at infraorbital foramen
- ipsilateral canine
- ipsilateral incisors
Where is the caudal approach to infraorbital nerve blocks? What 3 structures are desensitized?
through infraorbital foramen via catheter to proximal end of the canal with pressure
premolars, canine, and incisors cranial to the end of the catheter within the canal
What landmark is used for mental nerve blocks? What structures are desensitized?
palpate through gingiva ventral to the first premolars
incisors and mandibular symphysis
What structures are desensitized with mandibular nerve blocks?
ipsilateral premolars, molars, canines, and incisors (entire mandible arcade on that side)
What are the 2 approaches to mandibular nerve blocks?
- intraoral submucosal injection at the ventromedial ramus with a mouth gag in place
- external ventral through the skin at the angle of the jaw with syringe parallel with table (with mouth gag)
What patients receive low end of the scale of doses used in dental blockades?
- felines
- debilitates animals
- vascularized/inflamed tissues
doses are fit to the site, rare excees 0.1-0.25 mLs
When are retro or peribulbar blocks used?
- pre-enucleation
- prove need of enucleation
What nerve is responsible for sensory innervation for ocular structures?
ophthalmic and maxillary divisions of trigeminal (V)
What 5 nerves are blocked with retro or peribulbar blocks?
- optic (II)
- oculomotor (III)
- trochlear (IV)
- ophthalmic and maxillary divisions of trigeminal (V)
- abducens (VI)
What is indicative of sensory blockade to the ocular structures?
- immobility of the eye
- vision loss
- pupil dilation
- decreased IOP
How is the inferior temporal palpebral nerve block performed?
- needle is bent mildly and placed at the inferior orbital rim
- needle is then advanced until a slight popping is felt, indicating entry into the conus
- advance further dorsally
(aspirate before injection)
How is the perimandibular nerve block performed?
needle is placed ventral to the dorsal aspect of zygomatic arch and advanced dorsally
How is the periorbital ligament nerve block performed?
- needle is inserted craniomedial to the periorbital ligament that bridges the temporal and zygomatic bones
- directed toward opposite TMJ
How does wound soaker and CRI opioids compare in cases that require otic blocks?
WOUND SOAKER = less side effects, lower pain scores, lesser sedation
MORPHINE CRI = more side effects
Occipital nerve and U block:
When are brachial plexus blockades indicated? What are 3 common approaches?
analgesia of forelimb, axilla, and cranial thorax/sternum for forelimb, axillary, and scapular surgery or palliative care to OSA
- traditional (preshoulder) lateral recumbency
- dorsal recumbency
- paravertebral
How is the animal positioned for pre-shoulder brachial plexus blockade? How is it performed?
lateral recumbency with affected limb up
- needle inserted slightly proximal and medial to shoulder joint
- directed caudally and slightly ventrally, parallel to costochondral junctions
How is the animal positioned for axillary brachial plexus blockade? What is the triangle of interest?
dorsal recumbency with legs relaxed
- sternocephalicus (avoid jugular vein!)
- brachiocephalicus
- pectoral muscle
What are 3 injection sites used for paravertebral brachial plexus blockade?
- cranial to C6 transverse process
- caudal to C6 transverse process
- dorsal to head of first rib at an acute angle
Where are distal nerves palpable? How is the anesthetic placed?
under skin above tendons
perineurally - above or dorsal to tendons
When is a Bier block performed? How is it done?
distal procedures under 1 hour —> NOT IN CATS
- desanguination with Esmarch bandage
- place tourniquet proximally (can only remain 10-15 mins)
- remove Esmarch
- place needle above tendons of the carpus dorsally or palmarly
Psoas compartment vs paravertebral flank approach:
psoas = 1, needle angled cranially
paravertebral = 2, needle angled craniomedial
both use transverse process as a landmark
What is the difference between epidurals and spinals?
deposition of local and opioids above the dura
depisition of local and opioids subarachnoid, below the dura and arachnoid membrane
How are patients positioned for epidurals? What landmarks are used? Where is the needle placed?
sternal or lateral
L7/S1 interspace: craniodorsal ilium wings and tiny spine of L7
placed in site of deepest depression behind spine of L7
How is the needle advanced with epidurals? What are 4 signs of proper placement?
- needle perpendicular to skin with a mild cranial angle
- bevel is oriented towards either leg
- air leakage
- “whoosh” test
- “hanging drop” test
- “loss of resistance” technique with specialized syringes that allow plunger to move without friction
What specific areas of the hindlimb do femoral and sciatic blocks cover? 2 contraindications?
- FEMORAL = proximal lateral and distal medial
- SCIATIC = remainder of limb
- compartmental syndrome
- ongoing limb hemorrhage
How is the patient positioned for sciatic nerve blocks? What 2 landmarks are used? How is the needle placed?
lateral recumbency with affected limb up
- greater trochanter
- ischiatic tuberosity
inserted between the 2 landmarks towards the foot 1/3 of the distance from the trochanter to the tuberosity
What landmark is used for peroneal nerve blocks?
proximal lateral tibia - distal and caudal extensor groove and cranial head of fibula
- palpate under skin to feel neurovascular bundle
What landmark is used for tibial nerve blocks? What 2 sites can be injected?
distal tibia near the calcanean tendon web and lateral saphenous vein
- caudal to femur and cranial to vein
- caudal to vein and cranial to tendon complex
