UNIT 8 Regional Flashcards
What are the 5 divisions of the spinal column, and how many vertebrae are present in each?
cervical: 7
thoracic: 12
lumbar: 5
sacral: 5 fused
coccygeal: 4 fused
know the anatomy of the vertebrae
spinous process connected via lamina to transverse processes
pedicles connect to the vertebral body
all surround the vertebral foramen
what are the anatomical borders of the facet joint?
formed by the superior articular process of one vertebrae and the inferior articular process of the one directly above it.
injury to the facet can compress the spinal nerve that exits the respective intervertebral foramina, causing pain & muscle spasm along the associated dermatome
order the 5 ligaments of the spinal column from posterior to anterior
supraspinous ligament interspinous ligament ligamentum flavum posterior longitudinal ligament anterior longitudinal ligamnet
what ligaments are penetrated during midline approach to the epidural space? How about the paramedian approach?
midline:
- supraspinous
- interspinous
- ligamentum flavum
paramedian
- ligamentum flavum
list all of the structures & spaces b/n the skin and the SC as they would be encountered during a subarachnoid block
skin subcutaneous tissue muscle supraspinous ligament interspinous ligament ligamentum flavum dura mater arachnoid mater pia mater
what are the boundaries of the epidural space?
cranial border = foramen magnum
caudal border = sacrococcygeal ligament
anterior border = posterior longitudinal ligament
lateral border = vertebral pedicles
posterior border = ligamentum flavum, vertebral lamina
What happens when you accidentally inject LA into the subdural space during a SAB? How about during an epidural?
subdural space is a potential space b/n the dura and arachnoid mater
epidural dose injected into the subdural space –> high spinal w/ delayed onset (15-20mins)
spinal dose injected into the subdural space –> failed block
What is Batson’s plexus, and what is it’s significance?
the epidural veins
they drain venous blood from the SC. valveless. pass through the anterior and lateral regions of the epidural space.
obesity & pregnancy increase intraabdominal pressure = plexus engorgement. This is associated w/ an increased risk of needle injury or cannulation
What is the plica mediana dorsalis, and what is its significance?
while its existence remains controversial, many speculate that a band of connective tissue courses b/n the ligamentum flavum & dura mater
if it does exist, it could create a barrier that would impact the spread of medications w/in the epidural space.
it has long been considered the culprit for difficult epidrual catheter insertion as well as unilateral epidural blocks
what ligament covers the sacral hiatus? What is the significance of this?
sacrococcygeal ligament
this ligament is punctured during the caudal approach to the epidural space.
What is a dermatome, and which ones are important to know as you assess a neuraxial anesthetic?
dermatome = area of skin that is innervated by a spinal nerve
C6 = thumb C7 = 2nd & 3rd digits C8 = 4th & 5th digits T4 = nipple T6 = xiphoid T10 = umbilicus T12 = pubic symphysis L4 = anterior knee
compare and contrast the site of action for spinal vs. epidural anesthesia.
spinal
- primary LA action is on the myelinated preganglionic fibers of the spinal nerve roots
- LA also inhibit neuronal transmission in the superficial layers of the SC
epidural
- LA must diffuse through the dural cuff before than can block the nerve roots
- LA also leaks through the intervertebral foramen to enter the paraverterbral area, where they cause multiple paravertebral blocks
what factors do and do not contribute to the spread of LA in the subarachnoid space?
DO
- baricity
- patient position
- dose
- site of injection
- volume & density of CSF
DONT
- barbotage
- increased intraabdominal pressure
- speed of injectin
- bevel orientation
- vasoconstrictor addition
- weight
- gender
what is the primary determinant of spread for epidural anesthesia?
volume
discuss the differential blockade of spinal anesthesia
different types of nerves have different sensitivites to LA blockade
- autonomic first
- sensory second
- motor last
why is this important? autonomic blockade is 2-6 dermatomes higher than sensory block & sensory blockade is 2 dermatomes higher than motor block
How is differential blockade different w/ epidural anesthesia?
there is no autonomic differential blockade w/ epidural anesthesia
sensory blockade is 2-4 dermatomes higher than motor
compare and contrast nerve fibers in terms of subtype, myelination, function, size, conduction velocity, and block onset.
Aalpha
- heavy myelination
- skeletal m motor + proprioception
- largest
- fastest
- last for block onset
Abeta
- heavy myelination
- touch, pressure
- second largest
- second fastest
- last for block onset
Agamma
- medium myelination
- skeletal m tone
- medium size
- medium velocity
- second to last for block onset
Adelta
- medium myelination
- fast pain, temp, touch
- medium size
- medium velocity
- second to last for block onset
B
- light myelination
- preganglionic ANS
- medium size
- medium velocity
- first for block onset
C
- no myelination
- postganglionic ANS, slow pain, temp, touch
- small size
- slowest velocity
- second for block onset
discuss the CV effects of neuraxial anesthesia
sympathectomy –> vasodilation in arterial & venous circulations, although predominantly affects venous capacitance vessels
- -> decreased preload, CO, and BP
- volume loading w/ approx 15mL/kg and vasopressors will minimize hypotension
bradycardia is caused by
- T1-T4 preganglionic cardiac accelerator fiber blockade
- bezold-jarisch reflex
- unloading of stretch receptors in the SA node
discuss the respiratory effects of neuraxial anesthesia
in healthy patients, there is negligible effects on MV, Tv, rr, dead space, and ABG
accessory muscle function is reduced + abdominal muscles (cough function impairment)
- particularly important w/ COPD
how does neuraxial anesthesia affect the neuroendocrine response to stress?
by inhibiting afferent traffic originating from the surgical site, it diminishes the surgical stress response.
this reduces circulating levels of catechols, RAAS, glucose, TSH, and GH
how does neuraxial affect GI function?
the gut receives PSNS innervation from CN V and SNS innervation from the sympathetic chain b/n T5-L2
- inhibition of the sympathetic chain allows PSNS function unopposed
- -> sphincter relaxation & increased peristalsis
how does neuraxial anesthesia affect renal & hepatic blood flow?
as long as systemic BP is maintained, HBF & RBF are unchanged
what is the risk of neuraxial anesthesia in the patient w/ coagulopathy? What lab values are considered contraindications to a neuraxial technique?
risk of spinal or epidural hematoma
platelet <100K
PT, aPTT, and/or bleeding time twice the normal value
What cardiac pathologies present a risk of hemodynamic collapse w/ neuraxial anesthesia?
valve lesions w/ fixed SV:
- severe AS
- severe MS
- hypertrophic cardiomyopathy
what is the risk of a neuraxial technique in the patient w/ intracranial hypertension?
there is an increased chance of brain herniation w/ sudden changes in CSF pressure
what is the relationship b/n neuraxial anesthesia & MS?
classic teaching suggests that epidural is ok, but intrathecal may exacerbate symptoms - no good supporting data however.
what is the specific gravity of CSF? What factors increase and decrease the spec gravity of CSF?
1.002-1.009
increase:
- hyperglycemia
- uremia
- high protein content
- advanced age
- colder temperature
decrease:
- liver disease
- jaundice
- warmer temperature
what is baricity, and how does it influence your selection of LA?
baricity describes the density of a LA solution relative to the CSF.
- isobaric: LA similar to CSF
- hyperbaric: LA higher density
- hypobaric: LA lower density
hyperbaric will sink, hypobaric will rise, isobaric will remain in place.
as a general rule, solutions in dextrose are hyperbaric, saline are isobaric, water are hypobaric.
how does a hyperbaric solution distribute in the sitting patient? How about the supine patient?
sitting = sacral nerve roots (i.e. saddle block)
supine = sacrum & thoracic -T4 (since these are the areas of kyphosis
How does an hypobaric solution distribute in the sitting patient? How about the supine patient?
sitting = will rise toward the brain (i.e. avoid this)
supine = lower lumbar region (area of lordosis).
- it will not float toward the cervical region bc this would first require it to sink into the thoracic kyphosis
what are the 2 classifications of spinal needles?
cutting tip & non cutting tip (pencil point & rounded bevel)
cutting point = Quincke
pencil point = Whitacre, Sprotte
rounded bevel = Greene
List 6 examples of spinal needles, and list the pros and cons of each.
cutting tip (Quincke, Pitkin)
- pros = requires less force
- cons = higher risk of PDPH, less tactile feel, needle more easily deflected, more likely to injure cauda equina
pencil point (Sprotte, Whitacre, Pencan) AND rounded bevel tip (Greene) - pros = lower risk of PDPH, more tactile feel, needle less likely to deflect, less likely to injure the cauda equina - cons = requires more force
what are the 3 different types of epidural needles & how are they different from each other
differ in the angle of the needle tip (notice that the needle angle increases in alphabetical order):
crawford = 0 degrees
hustead = 15 degrees
tuohy = 30 degrees
- this curvature + it’s blunt tip helps prevent dural puncture
How do you dose a caudal anesthetic in a child? an adult?
peds
- sacral block: 0.5mL/kg
- T10: 1mL/kg
- mid-thoracic: 1.25mL/kg
adult
- sacral: 12-15mL
- T10: 20-30mL
avoid midthoracic
what are the absolute and relative contraindications to caudal anesthesia?
absolute:
- spina bifida
- meningomyelocele of the sacrum
- meningitis
relative
- pilonidal cyst
- abnormal superficial landmarks
- hydrocephalus
- intracranial tumor
- progressive degenerative neuropathy
discuss the mechanism of action of neuraxial opioids.
inhibit afferent pain transmission in the substantia gelatinosa (lamina II) of the dorsal horn
neurotransmission is reduced by:
- decreased cAMP
- decreased Ca++ conductance (pre-synaptic neuron)
- increased K+ conductance (post-synaptic neuron)
epidural opioids diffuse systemically as well
do neuraxial opioids cause sympathectomy, skeletal m weakness, and/or changes in proprioception?
NO
discuss the commonly used intrathecal and epidural opioids
sufentanil
- intrathecal 5-10mcg
- epidural 25-50mcg
- epidural gtt 10-20mcg/hr
fentanyl
- intrathecal 10-20mcg
- epidural 50-100mcg
- epidural gtt 25-100mcg/hr
dilaudid
- epidural 0.5-1mg
- epidural gtt 0.1-0.2mg/hr
meperidine
- intrathecal 10mg
- epidural 25-50mg
- epidural gtt 10-60mg/hr
morphine
- intrathecal 0.25-0.3mg
- epidural 2-5mg
- epidural gtt 0.1-1mg/hr
rank the opioids from most lipophilic to most hydrophilic. How does lipophilicity affect rostral spread in the subarachnoid space?
most lipophilic: - sufentanil - fentanyl - meperidine - dilaudid - morphine most hydrophilic
more hydrophilic drug = less diffusion into systemic circulation, more rostral spread
more lipophilic drug = more diffusion into systemic circulation
compare and contrast PK/PD profiles of hydrophilic and lipophilic opioids used for spinal anesthesia.
hydrophilic
- stays in CSF longer
- extensive CSF spread w/ wide band of analgesia + more rostral spread
- acts only in substantia gelatinosa
- delayed onset 30-60min
- DOA longer 6-24hrs
- less systemic absorption
- early & late resp depression
- higher incidence of N/V, pruritis
lipophilic
- stays in CSF shorter
- minimal CSF spread w/ narrow band of analgesia + less rostral spread
- acts in substantia gelatinosa and systemically
- fast onset 5-10mins
- shorter DOA 2-4hrs
- more systemic absorption
- only risk of early resp depression
- lower incidence of N/V, prutritis
What are the 4 most important side effects of neuraxial opioids? Which is the most common?
- pruritis (most common)
- respiratory depression
- urinary retention
- N/V
Which LA can reduce the efficacy of epidural opioids?
chloroprocaine
Which neuraxial opioid can reactivate herpes simplex labialis?
epidural morphine
- best explained by cephalad spread of morphine to the trigeminal nucleus
- usually presents 2-5 days after epidural morphine administration
describe the patho & presentation of PDPH
puncturing the dura causes CSF to leak from the subarachnoid space. As CSF pressure is lost, the cerebral vessels dilate + the brainstem sags into the foramen magnum, stretching the meninges & pulling on the tentorium
–> PDPH
classic presentation: fronto-occipital HA +/- N/V, photophobia, diplopia, tinnitus. Supine brings relief.
Discuss the risk factors for PDPH
younger age pregnancy female cutting point needle larger diameter needle multiple dural punctures using air for LOR w/ epidural needle perpendicular to long axis of meninges
how do you treat PDPH?
bed rest hydration NSAIDs caffeine (cerebral vasoconstriction) epidural blood patchy
not opioids
how do you perform an epidural blood patch? What is the success rate?
90% success rate/patch
- if HA doesn’t resolve after 2 blood patches, other etiologies should be sought
technique:
sterile withdrawal of 10-20mL of autologous venous blood is injected into the epidural space (stop injecting when pressure is felt in legs, buttocks, or back)
what are the most common side effects of an epidural blood patch?
backache
radicular pain
what is the primary risk of neuraxial anesthesia in the anticoagulated patient? How does this complication present?
risk of epidural hematoma is similar during block placement and catheter removal.
epidural hematoma can cause paralysis. presenting symptoms = LE weakness, numbness, low back pain, bowel/bladder dysfunction.
- surgical decompression w/in 8hrs = best chance of recovery
know how long to hold off neuraxial anesthesia after various drugs:
- NSAIDs
- aspirin
- abciximab
- clopidogrel
- ticlopridine
- heparin
- enoxaparin
- warfarin
- tPA, other thrombolytics
- herbal therapies
NSAIDs & aspirin, herbals (garlic, ginkgo, ginseng)
- ok to proceed if pt has normal clotting mechanism & is not on any other blood thinners
abciximab: 1-2 days
clopidogrel: 7 days
ticlopidine: 14 days
SQ heparin: ok to proceed if all else WNL IV heparin: - hold 2-4hrs pre-blcok - hold 1hr post-block - hold 2-4hrs after removal
enoxaparin: 12-24hrs depending on dosing
warfarin: 5 days (ok to remove cath if INR<1.5)
thrombolytics: absolute contraindication
compare and contrast the level of the conus medullaris and dural sac in the adult vs. the infant
SC ends in a taper at the conus medullaris
- adult L1-L2
- infant L3
subarachnoid space terminates at the dural sac
- adult S2
- infant S3
what is the cause of cauda equina syndrome? What factors increase the risk?
cause = neurotoxicity is the result of exposure to high concentrations of LA
factors that increase risk:
- 5% lido
- spinal microcatheters (since they focus LA on a small area of the cord)
how does cauda equina syndrome present? What is the treatment?
s/s: bladder & bowel dysfunction, sensory deficits, weakness, and/or paralysis
tx: supportive
what is the cause of transient neurologic symptoms? What factors increase the risk?
cause: patient positioning, stretching of the sciatic nerve, myofascial strain, muscle spasm
- highly unlikely that neurotoxicity causes TNS
factors that increase risk:
- lidocaine
- lithotomy position
- ambulatory surgery
- knee arthroscopy
How do transient neurologic symptoms present? What is the treatment?
s/s:
- severe back & buttock pain that radiates to both legs
- generally develops w/in 6-36hrs & persists for 1-7 days
tx: NSAIDs, opioids, trigger point injections
what is the most common organism responsible for post-spinal bacterial meningitis?
ways organism can infect the CSF:
- failure of aseptic technique
- bacteremia at time of SAB
streptococcus viridans is one of the most common culprits. it is commonly found in the mouth, and this is why it’s critical to wear a mask when performing neuraxial
What is the best way to prepare the skin prior to neuraxial anesthesia?
chlorhexidine, isopropyl alcohol, or iodine solutions
- chlorhex is neurotoxic, so let it dry completely
what are the 5 main components of the brachial plexus?
roots (5) trunks (3) divisions (6) cords (3) branches (5)
how many trunks are in the brachial plexus? Which nerve roots give rise to each trunk?
3: superior, middle, inferior
C5-6: superior
C7: middle
C8-T1: inferior
How many divisions are in the brachial plexus? Which nerve roots give rise to each division?
6 divisions - 3 posterior, 3 anterior
C5-C7: anterior divisions of superior and middle trunks
C8-T1: anterior division of inferior trunk
C5-T1: all 3 posterior divisions
How many cords are in the brachial plexus? Which nerve roots give rise to each cord?
3 cords: posterior, lateral, medial
C5-C7: lateral cord
C8-T1: medial cord
C5-T1: posterior cord
how many terminal branches are in the brachial plexus? Which roots give rise to each branch?
MSCN C5-7 axillary C5-6 median C5-T1 radial C5-T1 ulnar C8-T1
where do the roots turn into trunks?
just beyond the lateral border of the scalene muscles
where do the trunks turn into divisions?
underneath the clavicle and over the first rib
where do divisions turn into cords?
where the brachial plexus goes under the pectoralis minor muscle
where do the cords turn into terminal branches?
in the axilla
describe the sensory innervation of the upper extremity
review picture
how do you assess each branch of the brachial plexus (sensory & motor)?
axillary
- pinch lateral aspect of shoulder
- arm abduction
musculocutaneous
- pinch lateral aspect of forearm
- elbow flextion
median
- pinch index finger
- thumb opposition
radial
- pinch web space b/n thumb & index finger
- elbow extension, wrist & finger extension
ulnar
- pinch pinky finger
- pinky finger abduction
in addition to a brachial plexus block, which nerve must also be anesthetized to foster the tolerance of an upper extremity tourniquet?
intercostobrachial block
- it arises from T2
- field block is required to block this nerve
- w/ arm abducted & externally rotated, begin at deltoid prominence and move inferiorly (5mL)
what types of surgical procedures are well suited for an interscalene block? Which are not?
shoulder & proximal upper extremity procedures
not best for those below the level of the elbow since it often spares C8-T1 (which innervates portions of the forearm and hand)
be able to identify brachial plexus anatomy on ultrasound for an interscalene block.
(scalene muscles, “stop sign”)
which approach to the brachial plexus is most likely to cause phrenic nerve paralysis? What are the clinical implications of this?
nearly always blocked when performing an interscalene block, resulting in ipsilateral hemiparesis of the diaphragm
- in healthy pts, this rarely results in respiratory compromise
- in those w/ respiratory disease (COPD), this may result in severe dypsnea, hypercapnia, and hypoxemia.
which approach to the brachial plexus is most likely to cause Horner’s syndrome? What are the clinical implications of this?
stellate ganglion (cervicothoracic ganglion) is located at C7
- this structure is often blocked during the interscalene approach –> Horner’s syndrome (ptosis, miosis, anhidrosis)
- Horner’s syndrome indicates a successful block
discuss the relationship b/n shoulder arthroscopy, interscalene blocks, and hypotensive bradycardic episodes.
Bezold-Jarisch reflex is the proposed mechanism for hypotensive, bradycardic episodes during shoulder arthroscopy w/ interscalene blocks
s/s = bradycardia, hypotension, syncope
theory: venous pooling in LE reduces venous return
combination of unloaded ventricle, SNS stimulation, an epi uptake from the block results in a profoundly underfilled ventricle that slows it’s rate to increase diastolic filling time
which types of surgical procedures are well suited for a supraclavicular block? Which are not?
provides a dense block for surgeries at or below the level of the elbow
not ideal for shoulder procedures since it doesn’t reliably anesthetize the suprascapular nerve (arising from the proximal upper trunk)
be able to identify brachial plexus anatomy on ultrasound for a supraclavicular block
(pleura, first rib, subclavian artery, nerves)
what is the greatest risk of a supraclavicular block? Why?
pneumothorax
- cupola of the lung is just medial to the first rib, it is higher on the R side
- tall thin pts have a higher risk
- consider PTX if pt coughs or complains of CP during needle insertion or manipulation
what types of surgical procedures are well suited for an infraclavicular block? Which are not?
upper extremity below the elbow
shoulder & upper arm aren’t anesthetized
be able to identify brachial plexus anatomy on ultrasound for an infraclavicular block
(pectoralis major & minor, subclavian artery w/ cords surrounding it, & subclavian vein)
describe the relationship of the terminal branches relative to the axillary artery.
musculocutaneous is anterior & lateral
median is anterior & medial
radial is posterior & lateral
ulnar is posterior & medial
be able to identify brachial plexus anatomy on ultrasound for an axillary block
(axillary artery w/ terminal branches surrounding, coracobrachialis muscle, humerus)
which nerve is most likely to be missed during an axillary block? Which terminal branch is not included in an axillary block?
musculocutaneous resides in the coracobrachialis muscle; it’s not part of the neurovascular sheath that surrounds the axillary artery
- it must be blocked separately
axillary nerve is not included in the axillary block
what types of surgical procedures are well suited for an axillary block? Which are not?
upper extremity distal to the elbow
not recommended for procedures below the elbow
how do you block the radial nerve in the forearm?
3-5mL LA injected b/n teh biceps tendon and the brachioradialis
how do you block the ulnar nerve at the elbow?
elbow is flexed and 3-5mL LA is injected b/n the olecranon & medial epicondyle of the humerus
- using too high a volume can compress the ulnar nerve, resulting in ischemic injury
how do you block the median nerve at the forearm?
in the antecubital fossa, 3-5mL LA is injected medial to the brachial artery
- avoid this block in those w/ carpal tunnel syndrome
how do you block the radial nerve at the wrist?
subQ injection (field block) of 10mL proximal to the radial styloid - a field block is used because there are several branches of the radial nerve at this point in the wrist
how do you block the ulnar nerve at the wrist?
inject 3-5mL medial to and below the flexor carpi ulnaris tendon
- confirm negative aspiration d/t proximity to the ulnar artery
how do you block the median nerve at the wrist?
inject 5mL between the flexor carpi radialis tendon & the flexor palmaris longus tendon
How do you perform a Bier block?
- place a double cuff tourniquet on the pt; do not inflate it
- place 22g PIV distally
- elevate extremity x1-2mins for passive exsanguination
- wrap Esmarch bandage to further exsanguinate the extremity
- inflate the distal cuff
- inflate the proximal cuff
- deflate the distal cuff
- remove escmarch bandage
- inject LA (large volume of dilute; ex 50mL of 0.5% lido)
tourniquet pressure should be approx 250 (or 100 greater than SBP)
- can inflate the distal cuff & deflate the proximal cuff if pt is experiencing tourniquet pain
A patient complains of tourniquet pain when using a double cuff tourniquet under Bier block. List the sequences of deflating one of the cuffs and inflating the other cuff.
tourniquet pain typically begins at 45-60mins after inflation, and this is the most common reason why a patient would be unable to tolerate a procedure lasting >1hr
- inflate distal cuff
- deflate proximal cuff
For the patient who received a Bier block, when can you deflate the tourniquet?
toxicity is the most significant risk of IVRA; tourniquet must be inflated for a minimum of 20mins post LA injection.
<20 mins = don’t deflate
20-40mins = deflate, immediately reinflate, then deflate again at 1min
>40mins = ok to deflate
Name the 6 terminal branches of the lumbar plexus.
lumbar plexus arises from the anterior rami of L1-L4, w/ an occasional contribution from T12. It gives rise to 6 nerves
"I Invariably Get Lazy On Fridays" Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Obdurator Femoral
What nerve roots give rise to each nerve of the lumbar plexus?
iliohypogastric L1 ilioinguinal L1 genitofemoral L1-L2 lateral femoral cutaneous L2-L3 obdurator L2-L4 femoral L2-L4
know the LE innervation
see picture
describe the anatomy of the psoas compartment.
The lumbar plexus is contained within a sheath inside the psoas compartment
at this point, the plexus is:
- lateral to the vertebral column
- anterior to the quadratus lumborum muscle
- posterior to the psoas muscle
What nerves are anesthetized by the psoas compartment block? What is another name for this block?
The psoas compartment block (lumbar plexus block) targets three major nerves of the lumbar plexus:
- lateral femoral cutaneous nerve
- femoral nerve
- obdurator nerve
this block is useful when neuraxial anesthesia is contraindicated and/or anesthesia to one LE is preferred
Discuss the anatomy of the femoral triangle
the femoral nerve arises from L2-L4, it remains in the groove b/n the psoas major and iliac muscles before entering the femoral triangle
inside the femoral triangle, the femoral nerve runs:
- deep to the inguinal ligament
- anterior to the iliopsoas muscle
- inferior to the fascia lata and fascia iliaca
The triangle is shaped like the “SAIL” of a ship:
- S = sartorius m
- A = adductor longus m
- IL = inguinal ligament
use “VAN” for the structures inside the triangle, medial to lateral
- V = vein
- A = artery
- N = nerve
Discuss the anatomy & innervation of the anterior and posterior branches of the femoral nerve.
the division occurs either just before or just after the nerve passes under the inguinal ligamnet
anterior branch innervates the ventral surface of the thigh & the sartorius muscle
posterior branch innervates the quadriceps m, knee joint, and its medial ligament before giving rise to the saphenous nerve.
be able to identify the key anatomy for a femoral nerve block on ultrasound
(femoral vein, femoral artery, femoral nerve, IPSM)
describe the innervation of the saphenous nerve. What are the implications of this in the context of surgery on the lower extremity?
saphenous nerve is the terminal branch of the posterior division of the femoral nerve
- it provides sensory innervation from the medial aspect of the knee to the medial malleolus
- there is no motor component
this block is useful when combined w/ a popliteal or ankle block
Describe the anatomy of the sciatic nerve
arises from L4-5 & S1-3
- it is actually two nerves (tibial & peroneal) contained w/in a sheath
- it exits the pelvis inferior to the piriformis m via the great sacrosciatic foramen
- it continues caudally, passing b/n the major trochanter & the tuberosity of the ischium into the lower 1/3 of the thigh. This is where it divides into tibial and common peroneal nerves.
Describe the relevant anatomy for a popliteal block
targets the sciatic nerve in the proximal popliteal fossa.
at this location, the sciatic n is posterior & lateral to the popliteal artery & vein, and is bordered medially by the semitendinosus & semimembranosus muscles, and laterally by the biceps fermoris muscle.
A “triangle” is formed in the posterior knee w/ the base being by the popliteal crease at the knee & the apex formed by the muscles converging.
be able to identify the key anatomy for a popliteal nerve block on ultrasound
(popliteal artery & vein, common peroneal & tibial)
name the 5 terminal nerves at the level of the ankle. What is the origin for each nerve?
each one is a branch of either the femoral or sciatic nerves.
- the 3 sensory nerves begin w/ an “S”
- the 2 mixed sensory and motor nerves don’t begin w/ an “S”
femoral: saphenous
sciatic: deep peroneal, superfiicial peroneal, sural, posterior tibial
describe the sensory innervation of the foot and ankle
see picture
where is the posterior tibial nerve blocked?
posterior to the medial malleolus
where is the sural nerve blocked?
posterior to the lateral malleolus
where is the deep peroneal nerve blocked?
between the tendons of teh anterior tibial and extensor digitorum longus muscles
where is the superifical peroneal nerve blocked?
anterior to the lateral malleolus
where is the saphenous nerve blocked?
anterior to the medial malleolus
at the level of the ankle, which nerve is not immediately adjacent to a vascular structure?
superficial peroneal nerve
all of the others are very close to an artery and/or vein, therefore blockade of the superficial peroneal is the least likely to result in an intravascular injection
