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
What are 6 precautions for cranial nerve blocks?
- cats and odd facial formations (alters uptake of CNS)
- inadvertent ocular injections
- intraoral debris entrainment leads to abscessation
- vascular uptake
- air emboli
- vasodilation possible with large volumes
What surgeries requires otic blocks?
- lateral ear canal resection
- pinna resection
- total ear canal ablation
- ventral bulla osteotomy
What 3 nerves provide pinna and caudal sensory innervation?
- auriculotemporal nerve (branch of trigeminal)
- occipital nerve (branch of cervical nerve II)
- greater auricular nerves (off cervical nerve II)
What are the 2 techniques for otic blockades?
- soaker catheter in surgical area
- greater occipital nerve and auriculopalpebral nerve (U) blockade
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
What are 3 contraindications for brachial plexus blockades?
- hind limb amputees
- clinical coagulopathy
- landmark obliteration
What are 3 precautions to brachial plexus blockades?
- entering the chest and causing pneumothorax
- entering axillary artery or vein
- paralysis of major weight bearers
What are 3 specific side effects associated with brachial plexus blockades?
- migration of injectate through vertebral foramen and into spinal meninges
- phenic nerve impairment
- Horners syndrome
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
Where is analgesia provided from axillary brachial plexus blockade? How is the needle advanced?
inclusive of humerus distally
ventrally inserted proximal and medial to the shoulder joint
Where is anesthesia provided with paravertebral brachial plexus blockade? How is the patient positioned? What is the goal?
mid-scapula distally
lateral recumbency with affected limb up
reach branches of spinal nerve PRE-plexus
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
What causes local anesthetic toxicity after paravertebral brachial plexus blockades? Horner’s syndrome? Diaphragmatic paralysis?
intrapleural or axillary artery/vein injection
sympathetic (stellate) ganglion anesthesia
phrenic nerve anesthesia
What is the most common cause of hematoma or nerve injury associated with paravertebral brachial plexus blockade?
vessel injury
blind injection
What are 5 indications for distal feet blockades?
- biopsy
- laceration
- declaw
- toe amputation
- nail and nail bed disorders
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
How is the needle prepated for intrapleural blockades? Where is it placed? How do you know you’re in the right spot?
attached to a syringe with saline prior to entry
dorsal most aspect of the ribs under the epaxials and injected caudal to rib
- create a meniscus
- as the pleural space is entered, fluid will be pulled into the thoracic cavity, making the meniscus drop and move with respirations
What is done once the catheter is placed in the intrapleural space?
- deliver dilute injectate very slowly over 3-5 mins
- roll the patient with the affected side down or into doral recumbence so the fluid is able to coat the dorsal most aspect of the pleural cavity
What are 5 indications for intrapleural blockade?
- lateral thoracotomies
- chest tube discomfort
- pancreatitis
- diaphragmatic hernia repair
- rib fractures
How are peripheral wound bed blockade indwelling catheters placed for thoracic wall issues?
subcutaneously tunnel the soaker catheter or epidural catheter down the thoracic wall over the ribs
What are 4 contraindications for intrapleural and intercostal blocks?
- cardiac arrhythmias
- clinical coagulopathies
- actively hemorrhaging chest drainages
- active hemothorax
What are 3 side effects associated with intrapleural or intercostal blocks?
- intrapulmonary injection causes vascular uptake, bulla formation, or bronchoconstriction
- sympathetic blockade
- vascular uptake
What are 3 reasons that toxicity levels are so much higher with intrapleural and intercostal analgesia?
- pleuritis and inflammation aid absorption
- major arterial and venus plexus concentration in chest = maximum absorption
- often deposited lose to the site of major constant acting muscle, like the heart
What are indications of abdominal paravertebral and psoas compartment blockades?
PV - laparoscopy flank approaches, flank lacerations, mammary/preputial injuries, cranial thigh surgery
PC - blockade of major lumbar plexus for hind limb surgery, coxofemoral surgery, cranial thigh (stifle) surgery, or psoas myopathy diagnosis
How do abdominal paravertebral blocks compare to line blocks? In what animals is this commonly done?
anesthetic deposited proximal and dorsal to the actual surgical site, creating a wall of analgesia based on dermatome nerve supply
large animals
Where is the small animal equivalent of abdominal paravertebral blocks injected? Why is it a lengthier technique?
inverted L at lumbar spine (7 blocks) = dorsal off midline approach at inerspinous space with needle perpendicular to skin
larger volume of anesthetic needed with multiple injection sites
What forms the psoas compartment? How is the block placed?
fusion of psoas major and minor that originate from L2/L3 transverse process and insert on the femur
- dorsal approach off midline at the interspinous space
- cranial angling off distal transverse processes
Psoas compartment vs paravertebral flank approach:
psoas = 1, needle angled cranially
paravertebral = 2, needle angled craniomedial
both use transverse process as a landmark
What are 4 cons to the psoas compartment block?
- technically difficult and time-consuming
- hard on obese patients
- non-specific
- expansion of muscle bed is seen with large volumes
What are some indications for epidurals?
hind end, abdominal, thoracic, or forelimb procedure and chronic pain
What are 5 contraindications for epidurals?
- coagulopathies
- spinal/pelvic fractures prohibit proper placement
- severe dermatitides
- meningitis, myelitis, encephalitis
- hypovolemia or uncontrolled shock with local anesthetics (NOT seen with opioids)
What are 4 major side effects seen with epidurals?
- immediate: hypovolemia with too much locals
- urinary retention with high doses of opioids
- decreased hair growth
- decreased motor function seen with lidocaine
What results from accidental subarachnoid and intravascular injection of epidurals?
respiratory depression, hypotension
systemic toxicity
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
When in epidural catheterization done? What solutions must be used? Can pumps be used?
longer-term analgesia
PRESERVATIVE-FREE - narcotics, local anesthetics, ketamine
yes
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
What side effect is associated with sciatic and femoral nerve blocks?
- incomplete stifle analgesia
- SCIATIC: intraneural injection
- FEMORAL: femoral artery puncture
How is the patient positioned for femoral nerve blocks? What are 4 landmarks?
lateral recumbency with affected limb up and extended behid
- femoral pulse isolated and pulled caudally
- pectineus caudal
- sartorius cranial
- iliopsoas proximally
How is a femoral nerve block placed?
needle is inserted cranial to the femoral artery and is advanced caudally toward the iliopsoas muscle (origin of the nerve)
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
What are 3 indications for tibial nerve blocks? What contraindication is common?
- distal tibial surgery
- hock surgery
- metatarsal and phalanges surgery
landmark difficulties
Local anesthetics such as lidocaine and bupivicaine work via
a. antagonizing beta receptors
b. agonizing alpha receptors
c. enhancing sodium channels within nerves
d. blocking sodium channels withing nerves
e. interacting with GABA receptor complex
D
Epidurals can be used to provide pain relief to any part of the body caudal to the shoulders with the appropriate dilution of local anesthetic and vascular support. This is due to the fact that as the solution ascends the spinal column, a variety of nerves are affected. All of the following are the types of nerves affected by local anesthetics (some more than others) EXCEPT:
a. motor nerves
b. parasympathetic nerves
c. sensory nerves
d. third generation ganglion nerves
e. sympathetic nerves
B
Small volumes of local anesthetics are often used in dental blocks because
a. small patients have dental disease
b. open sulci, hemorrhage, and close proximity of nerves to vessels often result in vascular uptake
c. syringes are small
d. teeth are tiny
e. needles are very tiny
B
The femoral nerve can be blocked through all of the following approaches except:
a. within hemoral triang;e
b. within lumbosacral plexus through a lumbar plexus (psoas block)
c. through quadriceps
d. through intercostal muscles
D
Three techniques that can be used for periorbital or retrobulbar blocks are:
a. perimandibular, tempral zygomatic, peribulbar
b. perimandibular, inferior temporal, palpebral
c. perimandibular, inferior temporal, periodontal
d. perimandibular, superior temporal, periodontal
e. perimandibular, inferior temporal palpebral, periorbital
E
A brachial plexus can be performed from all the following approaches except:
a. dorsal recumbency, needle insertion cranioventral to pectoral
b. lateral recumbency, insertion cranial and caudal to C6 transverse process
c. lateral recumbency, insertion medial to point of shoulder
d. lateral recumbency, insertion medial to the shoulder and aimed at costochondral junction
e. dorsal recumbency, insertion craniodorsal to pectoral
E
Epidurals are commonly administered via which intervertebral site in small animal patients?
a. L7-S1
b. S1-S3
c. L5-L6
d. S3;Cd1
e. L6-L7
A
All of the following are reasons to utilize local blocks in your anesthesia plan EXCEPT:
a. less hemodynamic dysfunction
b. reduced need for opioids, reducing opioid-related side effects
c. reduced inhalant need
d. earlier return to function
e. allows greater surgical exposure
A
Local blocks can be performed using all of the following except:
a. thermography
b. electrostimulation
c. US or echolocation
d. blind placement
e. anatomic landmarks
A
