Locoregional Flashcards
Peripheral Nerve Stimulation
Monophasic square wave electric current: nerves selectively stimulated depending on size
Large diameter axons (>0.15mA) more easily excited than small (>0.3mA), motor nerves stimulated at lower currents than sensory
Closer needle is to target nerve, lower electrical current required to elicit muscle response
At 0.2-0.6mA
if stimulating needle able to elicit contractions of effector muscle or groups, assumed that needle to nerve distance small enough that when LA injected sensory blockade will occur
PNS MOA
Negative electrode (black) serves as searching electrode, connected to the insulated needle
Positive (red) electrode connected to patient’s skin
When used with configuration, current will induce depolarization of target nerve, resulting in obvious muscle twitches
Minimal Intensity Required to Depolarize a Specific Nerve…
depends on distance between the tip of the needle, the nerve
Settings on the Nerve Stimulator
2Hz, initially set at 1-1.5mA then decrease current to 0 and confirm twitches decrease in intensity before twitch elicited at 0.5 – frequency 0.1-0.3ms
USG for LRA
high frequency linear array transducers: 10-15mHz
Higher frequency transducers achieve lower penetration, better resolution
Function of Gain?
amplification of signal that returns to transducer, optimizes image obtained so structures that are identified
Regulates brightness, contrast of received signal to modify black and white balance
Horner’s Syndrome DT LRA
Blockade of the sympathetic trunk at cervical dermatomes
Respiratory Depression DT LTA
Excessive migration of injectate
Intercostal nerve blockade
Phrenic nerve blockade - C5, C6, C7
Circulatory insufficiency at resp center
MOA - epidural
nerve roots as leave SC, travel out from intervertebral foramina
o Drug access to site of action depends on drug’s physical, chemical properties, volume, gravity, permeability, etc
What is contained within the epidural space?
potential space of nerves, blood vessels, fat
MOA - intrathecal
non-selectively affect roots of spinal nerves located in dural sac
o Distribution, extension affected by baricity of drug and patient positioning
Layers for Epidural or Intrathecal Injection
o Skin
o Subcutaneous Tissue
o Supraspinous ligament
o Interspinous Ligament
o Interacuate ligament, yellow ligament or ligamentum flavum
o Epidural Space
o (Dura Mater)
o (Arachnoid membrane)
o Subarachnoid space = intrathecal, CSF, intricate trabecular network
Will you reliably see CSF with intrathecal injections?
Will not always see CSF with dural puncture
Hydrostatic pressure within dural sac 4-5mm Hg, cannot overcome height of needle when in sternal recumbency
Do not aspirate - negative pressure will suck nerve roots into needle, false negative
Techniques to Confirm Correct Placement in Epidural Space
hanging drop
LOR
US
ENS
Running Drip
Length of block distribution: occipital-coccygeal length
o Measure OCL (cm) in dogs
o Define desired block extension in cm
o Calculate % of column to be blocked (cm to be blocked/OCL)*100%
o Obtain dose from nomogram
Bier Block
–Admin of LA into peripheral vein, surgical anesthesia for up to 90’
–Distal limb wrapped tightly to exsanguinate, tourniquet then applied proximal to injection site
o Tourniquet in place 20-25’ minutes
–Tissue distal will be desensitized
–Early release of tourniquet may result in transient increases in LA plasma concentration CNS, myocardial system toxicities
Suprascapular N
C6
Supra, infraspinatus
Extension of Shoulder
Advances Limb
Lateral Surface of Shoulder
Subscapular N
C6, C7
Subscapularis
Adduction, extension of shoulder
Musculocutaneous N
C7 > C6
Biceps brachii, Brachialis, Coracobrachialis
Flexion of elbow
Craniomedial surface of forearm, distal to elbow
Axillary N
LJ: C8, T1; C7, C8
Deltoid, Teres major/minor, Subscapularis
Shoulder flexion
Caudal surface of shoulder joint capsule, Cranial arm
Radial N
C8, T1
Triceps, extensor carpi radialis, Ulnaris lateralis, Digital extensors
Extension of elbows, carpal joint, digits
Lateral surface of elbow, dorsal surface of forearm, dorsal surface of digits
Median Nerve
C8 > T1
Flexor carpi radialis, SDF, DDF
Flexion of carpal joints, digits
Medial elbow
Medial, palmar surface of forearm
Palmar surface of digits
Ulnar N
T1, C8
Flexor carpi ulnaris, DDF
Flexion of carpal joints, digits
Somatic Innervation to the Abdomen
T10-T12 Intercostal Nerves
Costoabdominal N (T13)
Cranial iliohypogastric N (L1)
Caudal iliohypogastric N (L2)
Visceral Innervation to the Abdomen
T8-L3 segments
Sympathetic Chain
Splanchnic n
TAP Block
Ventral branches of spinal nerves T9-L2
Abdominal wall and underlying parietal peritoneum only = NO CONSISTENT VISCERAL ANALGESIA
Quadratus Lumborum (QL)
Ventral br spinal nerves (T13-L3)
splaninc nerves/sympathetic trunk (T11-L3)
abdominal wall
underlying parietal peritoneum/visceral content
Femoral N
L4, L5, L6
PNS: Stifle flexion (+hip extension)
Iliopsoas, Sartorius
Quadriceps
Sciatic N
L6, L7, S1
PNS: dorsiflexion or plantar extension of foot
Common Fibular/Peroneal
LST
Digital extensors, biceps Femoris
Flexion of tarsus, extension of digits
Tibial N
LST
Caudal tibial
Digital flexors
Extension of tarsus
Digital flexion
Horn Blocks: Cattle
THREE SITES (or one per HD)
Cornual br zygomaticotemporal (br of lacrimal, ophthalmic br of V) + supraorbital (lacrimal) + infratrochlear (nasociliary, ophthalmic)
Locations for Needle Placement for Horn Blocks in Cattle
Cornual br: dorsal to dorsal aspect of ocular rim
Supraorbital: supraorbital foramen
Infratrocholar: 2-3cm media from dorsal aspect
SE of horn blocks in cattle
Proximity of rostral auricular, zygomatic br of auriculopalpebral nerves to injection sites often results in blockade = relaxation of ear, inability to close eyelids
Horn Blocks in Large Adult cattle
Require ring blockade with the subcutaneous branches of the second cervical nerves around caudal aspect/at point level with ear base
Horn Blocks in Goats
TWO SITES
Cornual br of lacrimal N
Cornual br of infratrochlear N
Site for Blockade of Cornual br of lacrimal n (goats)
Halfway btw lateral canthus, lateral edge of horn base
Site for Blockade of Cornual br of infratrochlear n
halfway btw medial canthus, medial edge of horn base
Intervened L/7 Block
Caudal aspect of last rib - ventral aspect of lumbar vertebrate TPs - blocks transmission of pain from periphery to SC
Proximal Paravertebral
AKA Farquharson, Hall, Cambridge Block
Perineural injection of LA in proximity to SN as emerge from vertebral canal
LTP1-4 to block T13-L3
Distal Paravertebral
AKA Cornell, Magda, Cakala technique
Block dorsal, ventral br as cross over, under TP - Injury start at distal end of TP; LA deposited along process as needle advances toward spine
Bier Block
–Dosing: 0.5-0.15mL/kg; NO EPI
–Tourniquet should not be released <10’ after injection to minimize changes of AEs from systemic LA
–Tourniquet duration: 20-30 or 60-90’
Bier Block MOA
Injection of LA into superficial vein: once LA passes of out vasculature/into small veins surrounding nerves, diffuses into capillary plexiglass of endoneurium and vas nervoruum capillary plexi that extend intraneurally
