Diagnostic Nerve Blocks Flashcards
Why is local anesthesia used in horses?
To localize lameness
Where should you begin when doing nerve blocks?
Begin distally and work proximally (especially w/ perineural block)
Which direction should your needle be directed when doing locoregional blocks?
Distally- avoids injecting limb proximally and anesthesia diffusing up limb
Why should you avoid sedating a horse when using nerve block diagnosis?
This can change the gait and you need a baseline before blocking
Horses may have a more violent reaction to needles when mildly sedated (you may be at greater risk)
At what grades should you avoid using LA for lameness evaluation?
Grade I and IV
If the horse is too lame you risk catastrophic failure- never a reason to block
What are agents used in local anesthesia?
2% lidocaine
2% Mepivacaine (most common)
0.5% Bupivacaine
How long does mepivacaine last?
30 minutes-2 hrs. with a rapid onset
How long does Bupivacaine last?
5-6 hrs. –. NOT USED for DX!
This is used for shoeing manipulations/therapeutic effect
What are the four methods of LA nerve block?
Regional
Direct infiltration of site
Intraarticular
Perineural
What is the most common nerve block LA?
Perineural
T/F: Presence of skin sensation does NOT mean failure of block at nerve body
TRUE
Where do you inject your LA for a palmar digital block?
Right above collateral cartilage over palpable neurovascular bundle (palmar digital VAN)
What position should the leg be in when giving a palmar digital block?
Hold limb up- should be non-weight bearing
What are the anesthetized structures associated with palmar digital nerve block?
Entire sole Navicular apparatus ST of heel Coffin joint Digital portion of DDFT
What are some reasons of failure of palmar digital nerve block?
Adhesion between navicular bone and DDFT
OA of coffin bone
Accessory nerve supply from dorsal digital branches
What are the structures anesthetized in the abaxial/basi-sesamoid block?
Entire foot + P2 Distopalmar P1 Proximal & Distal Interphalangeal joints Distal SDFT & DDFT Distal sesamoidean ligament Digital annular ligament
What nerves does a low & high 4-point block anesthetize?
Lat/Med palmar & Lat/Med palmar metacarpal nerves
Where are your landmarks for the lateral/medial palmar metacarpal nerve block?
Between palmar MCIII and MCII and IV
Stay at distal aspect of splint bone- more associated with cannon bone
What are the landmarks for the L/M Palmar nerve block?
Between SL and DDFT
Why should the low 4-point block be a sterile prep?
Due to increased risk for DDFT sheath
What are the anesthetized structures in a low 4-point block?
Everything from fetlock distally
What nerve block anesthetizes the origin of the suspensory ligament?
Lateral palmar nerve block
Where should the lateral palmar nerve block be given?
Mediolateral direction on the distal 1/3 of groove along medial aspect of accessory carpal bone
May have resistance due to extra fascia here
What structures are anesthetized with a high 4-point block?
Suspensory ligament
Flexor tendons
MCIII, MCIV
What doe radiographs show when trying to localize lameness?
Identifies osseous abnormalities
How many views should always be done at the minimum?
4 views
2 obliques
1 lateral
1 DP
What is the only modality that provides real time evaluation of both ST and some bone?
US
Excellent for stifles
What is needed when ultrasounding superficial structures?
Stand-off pad
When is a nuclear scintigraphy indicated?
Lameness site cannot be determined (grad 1/intermittent lameness)
What is the pharmaceutical compound used in bone scans?
Technetium-99
What is the modality of choice when imaging bone-especially skull?
CT
What is the modality of choice when imaging soft tissue not accessible with US?
MRI
