Exam 1 - Nerve Blocks Flashcards
how can you avoid potential complications associated with nerve blocks?
proper restraint of the horse decreases the likelihood of needle breakage
proper prep of the site - avoid infecting synovial structures
when should you use diagnostic anesthesia in an equine lameness case?
to identify painful region when either obvious pathology is lacking or there is more than one lesion present
to direct diagnostics & imaging
what medication is most commonly used for nerve blocks in horses? how long does the block last?
mepivacaine (carbocaine) - 90-120 minutes
which medication used for nerve blocks is least safe for joints?
bupivacaine - chondrotoxic
what are some indications for using bupivacaine for nerve blocks in a horse?
may use in hostile patients, sending patients for a long ride home, or prior to surgery - has the longest duration of action 4-6 hours
what is regional/perineural diagnostic anesthesia useful for?
blocks articular & extra-articular structures - requires a systematic approach from distal to proximal but less prep/materials are needed
what is synovial diagnostic anesthesia useful for?
intra-articular/intra-thecal - more specific of a block that can target extra-articular structures
requires more prep/materials - aseptic technique
T/F: a synovial block may not block subchondral bone pain
true
how should you prep a patient for a regional nerve block?
quick prep - chlorohex/betadine for 3-5 minutes
removes surface debris
how should you prep a patient for a synovial structure block?
aseptic technique - prep for 10 minutes
can clip or not clip - doesn’t make a huge difference
what nerves are blocked by a PD block?
palmar/plantar digital nerves
how do you place your needle for a PD nerve block when taking into consideration the neurovascular bundle?
vein is most lateral
artery is middle
nerve is medial
where are your landmarks for a PD nerve block?
feel for the neurovascular bundle above the hoof cartilages
insert the needle distally about 1cm above the hoof cartilages
what should you do ten minutes after performing a PD block?
check your block for skin sensitivity with hemostats - can check for loss of deep sensitivity after skin sensitivity is gone
T/F: loss of skin sensitivity does not equal loss of deep sensitivity
true
what does it mean if after a PD block is performed, a horse isn’t responsive to hemostats but is responsive to hoof testers?
deep sensitivity is still present - need to wait longer
what structures are reliably anesthetized by a PD block?
navicular bone, navicular bursa, navicular apparatus, DDFT, frog, 1/3-1/2 sole, parts of the PIP/DIP, & skin
what are some potential complications associated with PD blocks?
hemorrhage
ineffective block - missed the nerve, not waiting long enough, injected IV/IA, or ineffective mepivacaine
blocking more than expected - diffusion
needle breakage - very very bad
inadvertent penetration of a synovial structure - digital flexor tendon sheath or palmar pouch of coffin joint
why is a PD block with the dorsal branches likely ineffective?
the dorsal branches don’t innervate the DIPJ/contributes little sensation within the foot
what is the benefit of performing a midpastern PD block?
allows for desensitization of the entire foot including the PIPJ
what is another name for the basilar sesamoid block?
abaxial sesamoid block
what nerves are desensitized by an abaxial sesamoid block?
palmar digital nerves at or near the proximal sesamoid bones
what structures are anesthetized by the abaxial sesamoid block?
everything in the PD block
DIPJ, PIPJ, distal sesamoidean ligaments, dorsal branches of the suspensory ligament, DDFT, SDFT, & +/- MCP joint
what landmarks are used for an abaxial sesamoid block?
palpate the neurovascular bundle at the abaxial border of each proximal sesamoid bone
direct the needle distally at this level
