Chapter 73 - Diagnostic and Regional anesthesia Flashcards
Mechanism of action of pain stimuli caused by an injury is transmitted to the CNS by peripheralnerves which ones?
myelinated A-δ- responsible for conduction of fast,sharp pain.
unonmyelinated C-fibers fordull, diffuse pain.
The majority of fibers concerned with nociceptive transmission are
C fibers
There are ≠ types of C-fibers mediate only:
pain
temperature
touch mediate only pain
and others mediate temperature + touch+ pain
How do LA work?
Local anesthetics (LA) block nerve conduction by preventing the increase in membrane permeability to sodium ions that occurs when nerves are stimulated.
The order and degree of neural blockade correlate with 3 factors name them
diameter
type of nerve fiber
degree of myelination
What are the first nerve fibers to block?
the 1st nerve fibers blocked are:
the B-fibers –> next the A-δ- and C-fibers -> last nerve fibers blocked are A-γ-, A-β-, and A-α3-fibers.
According to Weir and Strichartz development of blockade is:
sympathetic function 1st –> pin-pricksensation (touch Tº) –> motorfunction
Where does LA first diffuse when finds the nerve ?
As a LA diffuses into a nerve, it affects the fibers at its periphery 1st and those at its core last.
Name the different drugs for local anesthesia and time of action
Lidocaine 30 minutes to 3 hours
Mepivacaine from 90 minutes to 3 hours Bupivacaine from 3 to 8 hours
Ropivacaine reliably ameliorated lameness for 3hours
Liposomal bupivacaine approved in the USA for woundinfiltration in humans produced an anesthetic effect greater than 24 hours when used for a peripheral nerve block à good for standing surgery?
refregeration is contra-indicated why?
Inactivates methylparaben = prevention of bacterial growth
What can be added to LA to increase duration? what dose?
Epinephrine can be added o LA to increase the duration of LA +intensityDose epine 5 µg/mL0,1 mL of 1:1000 epine is added to 20 mL of LA = 1:200000 []Commercialy available LA with epine are less potent than the ones preparedin the hour.
What are the risks of adding epinephrine to lido?
Risks: necrosis of skin at injection site + white hair +tissue swelling
Describe palmar digital nerve block
volume of** 1.5 mL** (2 mL for very large horses) local anesthetic solution is deposited subcutaneously at the proximal border of the collateral cartilages
what does the block a branch of the palmar digital nerve, the ramus tori digitalis (ramus pulvinus) does?
result in selective desensitization of the navicular apparatus without loss of skin sensation in the heel region of the foot.
HOW? a needle is inserted immediately proximal and axial to the proximal margin of the collateral cartilage, **midway **between the palmar border of the DDFT and the palmar extent of the collateral cartilage, and is directed **parallel to the slope of the dorsal hoof wall **and the long axis of the digit.
Local anesthetic solution (2–2.5 mL) is injected on the axial side of each collateral cartilage
Low 4-Point Nerve Block
palmar metacarpal nerves are blocked by depositing 1 mL local anesthetic solution at the palmar surface of MCIII by inserting a needle distal to the button at the distal aspect of the second and fourth metacarpal (MCII and MCIV) (splint) bones
The palmar nerves are blocked by inserting the needle in a proximodistal direction, not too deeply so as to avoid entering the digital flexor tendon sheath inadvertently, and advancing the needle parallel with the skin in the** groove separating the SL and the DDFT total of 2 mL** of local anesthetic solution is deposited
Describe abaxial sesamoid nerve block
needle is inserted over each palpable nerve at the abaxial border of the proximal sesamoid bones and directed distally until the tip of the needle is level with the base of the proximal sesamoid bone
2 mL
High 4-Point Nerve Block
medial and lateral palmar nerves are generally blocked subfascially with the limb weight bearing, by inserting the needle perpendicular to the skin to the hub beneath the heavy layer of palmar metacarpal fascia (distal extent of the carpal flexor retinaculum) and dorsal to the DDFT, slightly distal to the level of the carpometacarpal (CMC) joint. Nerves are not palpable at this level because of the presence of the palmar metacarpal fascia (carpal retinaculum flexorum), but the position of the dorsal surface of the DDFT can be estimated from extrapolating the vertical groove between the suspensory ligament and the DDFT proximally. 2 to 3 mL of local anesthetic solution is injected at each site.
Medial and lateral palmar metacarpal nerves is at the same level relative to the CMC joint, but the limb is held with the carpus flexed.
The needle (21- to 23-gauge, 3.8-cm needle) is inserted axial to the head of MCII and MCIV perpendicular to the palmar cortex of MCIII, until it contacts bone.
A total of 2 mL of local anesthetic solution is injected on both sides of the limb.
variation of the subcarpal, high 4-point block
performing the medial palmar nerve block by using a** longer needle (38–50 mm)** and advancing it from the** lateral injection site towards the medial palmar nerv**e, dorsal to the DDFT.
A variation on the medial palmar metacarpal nerve block is to redirect the needle in a dorsomedial direction from a subcutaneous position, after having performed the lateral palmar metacarpal nerve block, towards the interface between MCII and MCIII until the needle contacts bone.
Lateral Palmar Nerve Block
2 tecniques, WB or flexed:
**
1) Lateral approach to the lateral palmar nerve (Wheat block)**
the lateral palmar nerve is blocked as it runs along the distopalmar border of the accessoriometacarpal ligament. A 25-gauge, 16-mm needle is inserted to its hub in a palmarolateral to dorsomedial direction at the distal aspect of the accessory carpal bone. A total of 5 mL local anesthetic
2) Medial approach can be blocked as it courses medial to the accessory carpal bone. 25-gauge, 16-mm needle is inserted perpendicular to the longitudinal vertical groove on the medial aspect of the distal third of the accessory carpal bone and advanced in a mediolateral direction until the needle contacts the bone. The needle is slightly withdrawn and 1.5 to 2 mL of local anesthetic is injected
Median and Ulnar Nerve Blocks
site for blocking the ulnar nerve is about **10 cm proximal to the accessory carpal bone in the groove that separates the ulnaris lateralis** and flexor carpi ulnaris muscles - total of **10 mL **of local anesthetic is injected through a 25- to 20-gauge needle inserted to a depth 1 to 2.5 cm (the nerve lies just under the antebrachial fascia).
Distal Interphalangeal (DIP) Joint mention how many approach
1) dorsal parallel approach
2) dorsal inclined approach
3) lateral approach
Describe Dorsal parallel approach
the needle is inserted parallel to the bearing surface of the foot through or immediately proximal to the** coronary band** through the digital extensor tendon
Describe Dorsal inclined approach
needle is inserted perpendicular to the skin surface immediately proximal to the coronary band - avoidance of needle placement through the highly innervated coronary band and accommodation of diverse foot shapes and positions.
Describe Lateral approach
site for needle insertion for the lateral approach is a depression in the proximal border of the lateral collateral cartilage that is palpable near the palmar border of the middle phalanx. The needle is inserted through the skin,** 2 cm above the palpable depression in the proximal edge of the lateral collateral cartilage. The needle is directed in a lateromedial direction, angled 45 degrees distally medially** and 20 degrees dorsally to penetrate the palmar pouch of the DIP joint, which is entered at a depth of penetration less than 2.54 cm.
Can the navicular bursa and DDFT sheath be inadvertently entered by the needle?
YEs if a needle longer than** 2.54 c**m is used, or if the procedure is performed with the limb held in a flexed position.
Podotrochlear (Navicular) Bursa has how many techniques?
distal palmar approach to the “navicular position”
lateral approach
distal palmar approach describe to navicular
Hickman foot block
20-gauge, 8.9-cm spinal needle is inserted** between the bulbs of the heel just proximal to the coronary band**, and the needle is advanced along a sagittal plane aiming for a point 1 cm below the coronary band, midway between the dorsal and palmar limits of the coronary band.
The spinal needle is advanced until the needle contacts bone (4–5 cm for most horses)
Take radiograph LM to check the position prior injecting 3 mL of anesthesia
lateral approach describe to navicular
foot in a Hickman foot block
microconvex ultrasound transducer placed longitudinally in the distal pastern region - tipped 45 degrees laterally, thereby coming to lie obliquely, axial to the lateral ungular cartilage, with the center beam pointing dorsally.
a 20-gauge, 75-mm spinal needle is inserted just proximal to the lateral collateral cartilage of the distal phalanx, between the palmarolateral border of the middle phalanx and the lateral border of the DDFT, and proximal to the navicular position.
The needle is advanced in a proximolateral to distomedial oblique trajectory in the frontal plane of the limb at an angle of approximately 45 degrees to the solar plane of the foot
Do not penetrate DDFT or lateral collateral sesamoidean ligament
Proximal Interphalangeal (PIP) Joint how many approach?
dorsal approach
dorsolateral approach
palmaroproximal approach
palmarolateral approach
dorsal approach to PIP
horse bearing weight on the limb
The needle is inserted on the dorsal midline anywhere from 1 cm distal to 1 cm proximal to an imaginary horizontal line drawn between the medial and lateral eminences on the distal end of the proximal phalanx and is directed slightly distally and medially
dorsolateral approach to PIP
needle is inserted anywhere between 1 cm distal to 1 cm proximal to the level of the lateral eminence on the distal end of the proximal phalanx at the edge of the common digital flexor tendon.
The needle is directed medially, parallel to the bearing surface to enter the dorsal pouch.
palmaroproximal approach to PIP
limb is held in flexion and the needle is inserted into a V-shaped depression formed by the palmar aspect of the proximal phalanx dorsally, and the lateral branch of the superficial flexor tendon as it inserts on the middle phalanx palmarly. The needle is directed distomedially at an angle of 30 to 45 degrees from the transverse plane
palmarolateral approach to PIP
the limb is held with the DIP and PIP joints in flexion. The needle is inserted immediately proximal to the lateral bony prominence on the proximopalmar border of the middle phalanx. The needle is inserted** perpendicular to the sagittal plane** close to the palmar border of the proximal phalanx and is directed medially, perpendicular to the long axis of the middle phalanx.
Digital Flexor Tendon Sheath (DFTS) how many approach?
can be entered at any of the lateral pouches evident along its length palmar/plantar axial
- sesamoid approach,
- basilar sesamoidean approach
- distal approach on the palmar/plantar aspect of the pastern between the proximal and distal digital annular ligaments where the deep digital flexor tendon lies subcutaneously.
How to access the distal pouch DFTS
access the pouch at this location, the tip of the needle must remain superficial to the deep digital flexor tendon
palmar/plantar axial sesamoidean approach DFTS
needle is placed at the level of the midbody of the lateral proximal sesamoid bone, 3 mm axial to its palpable palmar/plantar border and palmar/plantar to the palmar/plantar neurovascular bundle. The needle is advanced through the skin and palmar/plantar annular ligament of the MCP/MTP joint at an angle of 45 degrees to the sagittal plane, aiming toward the central intersesamoidean region, to a depth of 1.5 to 2.0 cm.
basilar sesamoidean approach DFTS
he MCP/MTP region is held in slight flexion, needle is inserted distal to the lateral proximal sesamoid bone into a palpable depression created by the base of this bone and the lateral border of the superficial flexor tendon. The needle is advanced in a lateromedial direction, approximately 45 degrees to the transverse plane, and in a distoproximal direction, approximately 45 degrees to the dorsal plane, to a depth of 1 cm or less.
Metacarpo-/Metatarsophalangeal (Fetlock) Joint how many approach?
collateral sesamoidean ligament approach
dorsal approach to the MCP/MTP
MCP joint basilar sesamoid
collateral sesamoidean ligament approach
the limb is held with the joint slightly flexed.
Landmarks for needle insertion are the lateral palmar/plantar aspect of the lateral condyle of MCIII/MTIII and the lateral articular margin of the lateral proximal sesamoid bone.
needle is inserted into this V-shaped gap and advanced in a direction perpendicular to the long axis of the limb
Figure 73-2. Needle positions for a palmar digital nerve block (a), abaxial sesamoid nerve block (b), palmar/plantar nerve block (c) and palmar/plantar metacarpal/metatarsal nerve block (d), and lateral palmar nerve block (e) are shown. The ramus communicans (f) connects the palmar nerves
Figure 73-3. Needle positions for a median nerve block (a), an ulnar nerve block (b), and a nerve block of the medial cutaneous antebrachii (c) are shown.
Figure 73-5. The limb is held with the foot in flexion in a Hickman foot block, for navicular bursocentesis with the needle directed to the navicular position (Verschooten approach).
Figure 73-6. A needle is placed in the proximal interphalangeal joint using a lateral palmar approach (a). A spinal needle is placed in the navicular bursa using the distal, palmar approach to the “navicular position” (Verschooten approach) (b) or an ultrasound-guided lateral approach (c)
