Peripheral Nerve Blocks Flashcards
hypoechoic background with hyperechoic lines. Compressible
Fat
Bright hyperechoic lines
Fascia
hypoechoic background with hyperechoic lines. Non-Compressible. Surrounded by hyperechoic lines
Muscle
Very bright hyperechoic line with anechoic region beneath.
Bone
Hyperechoic and hypoechoic. Honeycomb appearance. Above clavicle more hypoechoic and below clavicle more hyperechoic
Nerves
Postganlionic sympathetic and afferent sensory. Only unmyelinated nerve fiber. Autonomic, pain and sensation
C Fibers
Preganglionic sympathetic. Autonomic
B Fibers
Afferent sensory nerve. Pain and sensation
A(delta)
Afferents to muscles and joints. Proprioception
A(Beta)
Efferents to muscle spindles. Muscle Tone
A(gamma)
Efferents to motor and joints. Motor
A(alpha)
Nerve block onset
B >C & A(d) > A(g) > A(b) > A(a)
Nerve block recovery
A(a) > A(b) > A(g) > C & A(d) > B
LAST (LA Systemic Toxicity ) - Drugs not to use
B-Blockers, Ca Channel Blockers, or LAs
Dont give Propofol
Also, reduce ept to < 1mcg/kg
T or F. Heparin 5000 SQ BID and Aspirin/NSAIDs may be administered at any time with no restriction on regional.
True
In general must wait anywhere from __-__ half-lives after administration of anticoagulant before regional can be safely performed.
3-5 half lives
Kidney and Liver dysfunction means one should wait longer before regional can be safely performed
Current intensity = measured in __. You should start at ___ and dial down. When you get to < ___ it is ok to inject LA
mA, 1.5mA, 0.7mA
_____ is used foe sensory vs. motor differentiation and is especially useful in neuropathic patients
Pulse duration = duration of current.
Typical pulse duration is about ___microseconds - which will get motor without sensory involvement
100msec
may have to increase for neuropathic pts
___ = pulses per second.
Stimulation frequency (Hz) - 2 Hz is typically adequate
_____ = pulse duration at which threshold current amplitude is twice that of rheobase
Chronaxie
Important for nerve differentiation
_____ = lowest current amplitude with long or infinite pulse duration applied to depolarize (stimulate) a nerve.
Rheobase
Equation for current you need in order to stimulate a nerve
I = ______
I =Ir(1 + C/t)
I = Current Ir = Rheobase C = Chronaxie t = pulse duration
Block is done at the C5-C7 root/trunk level.
C8-T1 (ulnar nerve) spared.
Block acceptable for shoulder and top half of humerus)
Deltoid/Biceps twitch acceptable
Side effects (ipsilateral horner syndrome, SOB, and hoarseness)
Complications (epidural/subarachnoid spread, paralysis, respiratory failure)
Interscalene Block
Block is deeper than the other blocks of the brachial plexus. Thus technically more difficult to visualize with ultrasound
Acts at level of cords
The best block when performing and upper extremity catheter.
Sensory innervations from mid-humerus down.
Pneumothorax a major concern
Infraclavicular Block
Musculocutaneous nerve, ulnar nerve, median nerve, and radial nerve blocked
Technically more challenging because individual nerves have to be anesthetized
No risk of pneumothorax
Very difficult to place a catheter
Axillary Block
Spinal of the arm
Acts at the level of the divisions
Covers from the mid-humerus down.
Does not cover shoulder because the axillary nerve and dorsal scapular nerve are spared
Pneumothorax a real concern especially with the land-mark technique
Supraclavicular block
Median, Ulnar, and Radial nerves blocked
Easily done with nerve stimulation, landmarks, or ultrasound.
Great supplemental block if one of the brachial plexus blocks is incomplete
Wrist and Elbow blocks
Innervation to anterior thigh and medial aspect of lower leg.
Quadriceps contraction ideal (as opposed to sartorial twitch)
Anterior and Posterior division
Significant quadriceps weakness
Ideal for knee replacements and ACL reconstructions
Fascia iliaca block only blocks femoral, lateral femoral cutaneous, and obturator 50% of the time.
Femoral Nerve Block
In rare situations when there is considerable medial knee pain
Obturator nerve divides into anterior and posterior divisions which traverse through the adductor muscles.
Obturator Nerve Block
“Femoral nerve block from the back”
Reliably blocks femoral, lateral femoral cutaneous, and obturator nerves
Advanced block ( Complications include epidural and subarachnoid spread and retroperitoneal hematoma)
Lumbar Plexus Block (Psoas Compartment Block)
Difficult to see under u/s guidance
Sensory nerve to lateral aspect of thigh
Location is 2 cm medial and 2 cm inferior to anterior superior iliac spine
Lateral Femoral Cutaneous Nerve Block
The only unmylenated fibers we have
C Fibers
Visceral Pain
A-delta
Somatic Pain
C fibers
Smallest fibers
C fibers
___ fibers are stimulated at shorter pulse durations
motor (50-100 micro sec chronaxie)
___ fibers are stimulated at longer chronaxie
pain - A(d) - 170 micros sec and C fibers - 400 micro sec
Largest and most sensitive nerve in the body (anesthetized with the lowest concentration of local anesthetic and anesthetized for longest duration)
Easily injured (torturous course and low blood flow)
Posterior cutaneous nerve of the thigh can only be blocked with parasacral approach
Sciatic Nerve Block
Several different places nerve can be blocks (above knee, below knee and ankle)
Quadriceps sparing (purely sensory nerve)
Excellent for foot and ankle surgery
Saphenous Nerve Block
5 nerves blocked
- Saphenous (fem)
- Deep peroneal (sci)
- Superficial peroneal (sci)
- Posterior tibial (sci)
- Sural (sci)
Ankle Block
Excellent block for breast and thoracic surgery
u/s, landmark, or loss of resistance appropriate technique.
Pneumothorax, epidural or intrathecal spread real concerns
Paravertebral Nerve Block
If you are doing an interscalene block and your pt starts to hiccup, what should you do?
You hit the phrenic nerve - should aim more posteriorly and laterally
If you are doing an interscalene block and rather than getting a deltoid and bicep twitch, you get a shoulder raise, what does that mean?
stimulating accessory nerve - too posterior and need to aim more anteriorly
Excellent coverage T10 and below (subcostal tap if higher segmental coverage needed)
Umbilical surgeries will need a rectus sheath block
TAP Block
