Locoregional anesthesia in LA Flashcards
What are the common local anesthetic volumes used in LA
Approx. volumes for adult cattle/equine nerve blocks = 5-15 mL per site
Most common local anesthetic used = lidocaine
Sheep/Goats/Camelids = 4-5 mg/kg
Horses = 8 mg/kg
Cattle = 8 mg/kg
What does a corneal nerve block freeze LA
Dessnitizes horn
Blocks ophthalmic branch of trigeminal nerve: cornual nerve, +/- supraorbital and infratrochlear nerves
Uses: dehorning or horn injury repair
How do you do a cornual nerved block LA
Young cattle: palpate upper 1/3rd temporal ridge approx. 2-5 cm down from horn based–insert needle SQ, aspirate and inject 3-5 mL local anesthetic
Adult cattle (well-developed horns) = ring block around entire base of horn or three-point block to completely desensitize horn
Goats: TWO branches of cornual nerve
Must block BOTH to completely desensitize the horn
Technique: insert needle SQ at each site, aspirate and inject 2-3 mL lidocaine per site
Zygomaticotemporal (aka. lacrimal) branch: behind root of supraorbital process, halfway between lateral canthus of eye and lateral base of horn
Infratrochlear branch: dorsomedial margin of orbit, midway between medial base of horn and medial canthus of the eye
How do you freeze a LA eye
Sensory denervation of eyelid = must block 4 separate nerves
Upper eyelid: supraorbital (frontal), lacrimal nerves
Lower eyelid: zygomatic, infratrochlear nerves
Motor innervation to eyelid:
Palpebral nerve (branch of auriculopalpebral nerve) = must block to prevent blinking
What is the technique to freezing the upper eyelid in LA
Insert needle SQ at each site, aspirate and inject desired volume of local anesthetic
Supraorbital nerve: Dorsal to medial canthus of eye, medial to supraorbital ridge
Also Blocks part of palpebral nerve
Lacrimal nerve: Palpate lateral canthus and place needle pointing medial along dorsal orbit rim
What is the technique to freezing the lower eyelid in LA
Infratrochlear nerve: dorsal orbital rim near medial canthus (bony notch)
Zygomatic nerve: lateral aspect of lower orbit rim and supraorbital part of zygomatic arch (direct ventral)
Auriculopalpebral block is used for what in LA
Prevents blinking during surgery or ocular exams
Sensation to the eye is STILL PRESENT
must block all sensation to eye with 4-point blocks previously discussed
how do you perform a Auriculopalpebral block LA
Two Techniques: insert needle SQ, aspirate and inject desired volume of local anesthetic and each site
A: depression caudal to mandible at ventral edge of temporal part of zygomatic arch
B: most dorsal point of zygomatic arch
Retrobulbular block is used for what in LA
desensitizes ocular surface, globe and intraocular structures
Optic, oculomotor, trochlear, maxillary and abducens nerves
Surgical preparation should be done with iodine 1.25% solution and sterile eye wash
What are the uses and complications of retrobulbular blocks LA
Complications: Eye penetration, IV or intraneural injection, retrobulbar hemorrhage, proptosis, oculo-cardiac reflex, increased IOP, chemosis
Use: enucleation +/- evisceration, orbectomy
How do you perform a retrobulbular block in cattle
Bend 20-gauge, 9-cm needle into circular angle
Insert needle at 4 points around orbit (12, 3, 6, and 9 o’clock positions) and advance through soft tissues until bone of orbit is hit
Advance needle along orbit bone until needle is located behind the orbit (feel ‘pop’ sensation when entering retrobulbar cone)
Aspirate, then inject 5mL lidocaine per site (20 mL total)
How do you perform a retrobulbular block in horse
Palpate orbital fossa just caudal to posterior aspect of dorsal orbital rim
Insert 22-gauge, 3.5-inch spinal needle perpendicular to skin, advance until eye rolls dorsally in orbit and a ‘pop’ is felt (entering retrobulbar cone)
Insert needle 2-3 mm more, aspirate then inject 10mL lidocaine or bupivacaine
Maxillary nerve block freezes what and is used for in LA
Desensitizes maxilla bone, intraoral soft tissues, upper dental arch, upper lip and nostril, hard and soft palate
Uses: Extraction of maxillary teeth, maxillary sinus trephination, nasal cavity surgery
What are the complications of maxillary nerve blocks in LA
Complications: salivary gland or maxillary artery damage, nerve damage
How do you perform a maxillary nerve block in LA
Palpate infraorbital foramen
Insert needle approx. 3-4 cm into foramen
Aspirate then inject approx. 5mL local anesthetic
Inferior alveolar nerve block (aka mandibular block) freezes what is used when and complications in LA
Desensitizes entire ipsilateral mandible bone and soft tissues, lower lip and lower dental arcade
Complications: tongue desensitization
Uses: dental extractions for molars/premolars, mandibulectomies, mandibular fracture repairs, mass removals, etc.
How do you do a inferior alveloar nerve block in LA
Extra-Oral Technique: (most common)
- Estimate mandibular foramen location by imagining two intersecting lines: vertically down from caudal aspect of orbit AND horizontal line parallel to occlusal surface of lower cheek teeth
- Insert 18 gauge, 8–10- inch spinal needle along caudal mandible until you hit the bone
- Walk off the end of the mandible heading medially, insert needle by scraping along inner aspect of mandible until you reach intersection of lines previously discussed
- Aspirate, then inject desired volume of local anesthetic
Intra-Oral Technique:
- Attach 20-gauge, 1.5-inch needle (bent 20-30 degrees) to IV fluid extension set, and guide insertion into oral cavity with 12-inch pliers
- Insert needle into mucosa just caudal and above occlusal surface of 3rd mandibular molar (lateral to palate)
- Aspirate and inject desired volume of local anesthetic
What does a mental nerve block freeze in LA and how do you do it
Lower lip desensitisation only
Local anesthetic injected around mental foramen
Lower incisors to 3rd premolar desensitization = mandibular alveolar nerve block
Insert needle into mental foramen and advance into mandibular canal (ventromedial direction)
What is the purpose of Distal limb locoregional anaesthesia in LA
Purpose: specific nerve blocks used to diagnose lameness but also to provide analgesia to lower limb for surgical procedures
What does a digital nerve block do LA
Palmer (planter) nerves: dorsal to fetlock at sesamoids
Three nerves: anterior, middle and palmar/plantar digital nerves
Sensory to hoof, navicular bone and bursa, corium, frog, sole
How do you perfom a digital nerve block in LA
Palpate nerve running along palmar/plantar aspect of pastern (medially or laterally by vein/artery) → passes distally over flexor tendon
Place needle midway b/w coronary band and fetlock
Desensitizes posterior ⅓ foot
Abaxial (basilar) sesamoidean nerve block does what and how to preform LA
Desensitizes medial and lateral palmar (plantar) nerves
Palpate nerves as they pass proximal sesamoids
Blocks entire foot, back pastern and distal sesamoidean ligaments
Can result in partial numbing of fetlock
Low palmer (planter) nerve block desnesitizes what LA
structures distal to fetlock and fetlock joint
Does not block small area dorsal to fetlock joint
How do you do a low palmer/planter nerve block in LA
Approach: 4-point block (patient should be bearing weight on the limb of choice)
Medial and lateral palmar (plantar) nerves: between flexor tendon and suspensory ligament
Medial and lateral palmar (plantar) metacarpal nerves: between suspensory ligament and splint bone
