Lab Flashcards
What is the onset and duration of lidocaine?
Rapid onset, 1.5-3 hr duration
What is the onset and duration of Mepivicaine?
Rapid onset, 2-3 hour duration
What is the onset and duration of Bupivicaine?
Intermediate onset, 3-6 hr duration
-used for therapeutics (ex after surgery)
What is the most important thing when injecting anything into a joint?
STERILITY
Which local anesthetic is typically used for diagnostic analgesia in horses?
Mepivicaine
-lidocaine not used as much as it can cause more soft tissue reaction
If trying to block inflamed tissue, how may the results of your test be affected?
Acidic environments interfere with the action of local anesthetic, so you may not see as much of a response
When do you not want to block limbs for diagnostic purposes?
Severe lameness cases
What are sources of articular pain?
Synovium, joint capsule, articular/periarticular ligaments, periosteum, subchondral bone
-note that cartilage is not on the list as it has no nerve endings (but cartilage breakdown can cause inflammation of these other structures)
What is the goal of diagnostic analgesia?
Ideally block out all lameness to better localize the source
-always start distally and work proximally
T/F: you can do intrasynovial blocks in any order
True- as there is no risk of the analgesic agent blocking out other areas
What are some indications for performing joint blocks?
Significant effusion in the joint, severe pain after flexion test
What level of patient prep is required for perineural blocks?
Clean, brief PI/alcohol scrub, never touch shaft or end of needle
-maybe want to be sterile if risk of entering synovial structure
What level of patient prep is required for intrasynovial blocks?
-Sterile prep: clip (if hair is dirty), 5-minute sterile scrub, wear sterile gloves
What needle size should you use for blocks when injecting subQ in small area?
22-25 ga
What needle size should you use for blocks when injecting into heavy fascia?
18 ga
T/F: Nerve blocks are typically done with the patients foot flat on the ground
F- legs should be lifted in most cases
In which anatomic direction should you direct your needle when doing blocks in the distal limb?
Distally to avoid the risk of the analgesic moving proximal
How should you judge improvement in diagnostic analgesia cases?
Very subjective. Make use of manipulation tests, circles
-aim for 100% improvement. baseline may switch to other side. Should always get 70% improvement or you need to block more to localize
What are some potential complications of perineural analgesia?
Perineural: Local swelling (hematoma, inflammation), regional swelling (cellulitis)
Intrasynovial: acute reactive synovitis (flare reaction), hematoma, infectious synovitis
What are some considerations for things to avoid when performing local anesthesia?
Blocked horses may be unsafe to ride during exam
-may unintentionally block the motor nerves (elbow, sacroiliac blocks)
-consider if there may be a fracture or incomplete fracture-Don’t block these horses. Image them first!
Describe the palmar digital block.
Blocks palmar digital nerves (medial and lateral)
-Blocks out 70-80% of the foot and the coffin joint (not blocking out coronary band)-includes heel, sole, and some of the soft tissue structures
-place needle just proximal to the heel bulbs
-use small volume
-to assess if block was affective, poke around heel bulbs and coronary band
Describe the dorsal ring block.
Targets the dorsal branches of the palmar digital nerves
-desensitized the entire foot and pastern
-may be more selective than the abaxial sesamoid block
-this block is not commonly done
Describe the basi-sesamoid and abaxial sesamoid block
Targets the palmar digital nerves proximal to their dorsal branching
-functionally similar to PD and dorsal ring block
- fetlock joint block possible with this -be sure not to go too high
Describe the low palmar/low 4 point block
Blocks the medial and lateral palmar digital nerves (subcutaneously) as well as the medial and lateral palmar metacarpal nerves (deep/axial)
-careful to avoid fletlock joint and digital flexor tendon sheath
-this block should completely desensitize the fetlock
Describe the high palmar/high 4-point block
Blocks the medial and lateral palmar and palmar metacarpal nerves
-blocks the carpal-metacarpal joint
What is an alternative to the high 4-point block?
Lateral Palmar/Wheat block
-requires medial palmar and dorsal ring blocks
-avoids the carpal joints but you are likely to enter carpal canal
Describe the distal interphalangeal joint block.
Provides analgesia to coffin joint, navicular bursa and toe of sole
Describe the navicular bursa block (podotrochlear)
Most specific block for navicular problems. Also blocks out toe of sole
-can use radiography to confirm positioning
Describe the proximal interphalangeal joint block
AKA pastern
Uncommonly performed
-synovial fluid is not commonly retrieved
-use up to 10 mL local anesthetic
Describe the proximal metacarprophalangeal joint bock (AKA fetlock)
lots of different approaches (dorsal, proximal palmar, collateral sesamoidean ligament)
- 10 mL, evaluate at 10 min
Describe the dorsal approach to the carpal joint block
Flex leg, can easily palpate joint
- can block proximal and middle (will also block out the distal)
-5-10 mL per joint
Describe the low plantar and distal blocks
Similar to forelimb counterparts
-action of reciprocal apparatus makes the flexed block more difficult
Describe the high plantar block
Blocks medial and lateral plantar and plantar metatarsal nerves
-dorsal ring block may be added to abolish dorsal cannon bone pain
-may be used to diagnose proximal suspensory desmitis
-must worry about blocking distal intertarsal joint
Describe blockage of the tarsometatarsal joint (hock)
Lateral approach
-insert needle just proximal to head of MT IV
-usually does not communicate with distal intertarsal joint
Distal intertarsal joint block
Difficult
-medial approach
-cunean tendon is marker
-stand on opposite side of horse
-fluid not usually obtained
Tarsocrural joint block
Communicates with the proximal intertarsal joint
-the saphenous vein overlies the dorsomedial pouch-avoid this
How do you inject the stifle?
Must inject all 3 joints separately (inconsistent which communicate from horse to horse)
What does the image created by a radiograph depend on?
Total number of xrays produced -mAs
Film focal distance- FFD (distance of tube to target)
Ability of Xray to penetrate the tissue- kVP
What are the main applications of radiography and what are its limitations?
Applications: evaluation of bone, some soft tissue
Limitations; 2D image of 3 D object leading to superimposition (take multiple views)
-30-50% change in bone density required for detection of radiographic changes
-superimposition of structures common
How should you prepare a horse for radiography?
They have to be weight bearing, clean area of interest, use proper restrain (often sedation), center machine on area of interest, be sure to take sufficient views
How should you evaluate a radiographic image?
Make sure its of adequate quality, the positioning is proper, there are no artifacts
-first evaluate from distance, then follow bone margins
-be sure to recognize breed and discipline differences
How can you age a lesion on a radiograph?
Difficult!
-new bone growth starts to occur 14 days before radiographic detection
-non-displaced fractures can take 10-14 days to become visible
What are some causes of focal demineralization?
Infection, osseous cyst-like lesion, chronic pressure, OC defect, neoplasia (not common in horses)
Define sclerosis
Increased radioopacity of bone
-Response to chronic mechanical stress of inflammation, walling off of infection, protection of weak areas of bone
What can contrast radiography be used for?
Used to highlight various structures
-can be used to estimate prognosis for a horse with laminitis (venogram)-poor contrast=poor prognosis
What are the advantages and disadvantages to using ultrasound?
Advantage: excellent soft tissue imaging, can see bone surfaces
Disadvantages: cant penetrate bone or gas
What are the main applications for using ultrasound?
Assessing tendons and ligaments, menisci, joints (capsule, cartilage surface, fluid), bursae, tendon sheaths, any soft tissue!
-diagnosing lung consolidation in pneumonia cases
How should you prep horses for ultrasound?
Clean area to be scanned, clip the hair, apply acoustic gel, make sure patient is weight bearing
T/F: smaller transducers are best for assessing superficial tissues?
False- these get deeper
How does nuclear scintigraphy work?
Radioisotope is ingested into the animal and it is tagged onto something to get incorporated into tissue of interest
-in the case of horses, we usually do this with bone by tagging it onto phosphorus
-the radioisotopes travel to areas of high metabolic activity
-gamma rays detect radiation
What are the indications for using nuclear scintigraphy?
Obscure or multifocal lameness
-to assess healing over time
What are the phases of the nuclear scintigraphy scan?
Vascular phase: image occurs immediately-what you see depends on local blood flow
Soft tissue: image 2-3 minutes post injection when bone uptake is beginning
BoneL 2-3 hours post injection-image depends on blood flow, permeability and the metabolic activity of the bone
What are you actually measuring during nuclear scintigraphy?
local bone metabolism
What are the advantages to nuclear scintigraphy?
Very specific for detecting early disease (but not specific), can scan entire body (but not cheap), can be used to monitor healing
Describe what CT scanning is?
Cross-sectional slices and 3D image reconstructed with computer (eliminates superimposition)
-results in better resolution of bone and soft tissues than radiographs, GA usually required
What are CT scans the most useful for?
Bone lesions, 3D fracture reconstruction, skull imaging (teeth and sinuses)
How are MRI images created?
Through excitation of hydrogen nuclei in body by a magnetic field. Energy is released during relaxation of the nuclei
-water and fat have the most hydrogen (high signal shows up white, low=black)
Name the advantages and disadvantages to MRI?
Advantages: superior to CT for soft tissues, can examine all tissues, excellent anatomical and physiologic info
Disadvantages: cost and size of patient, takes a long time, often have to be anesthetized, need to know where lameness is and if animal has implants
What are the main uses for MRI in horses?
Imaging from carpus and tarsus distally as well as head and cranial neck
