Central Blocks Flashcards
label these guys
- epidural space
- ligamentum flavum
- cauda equina
- cona medullaris
- dura mater
- arachnoid mater
- pia mater
- spinal cord
what connects the transverse process of a vertebra to the vertebral body?
pedicles
what connects the transverse process of a vertebrae to the spinous process?
lamina
where does the spinal cord terminate in most adults?
what is this called?
L1/L2 (depends on who you ask)
conus medullaris
what does the spinal cord transition into once it ends?
collection of nerves called the cauda equina
what is the importance of the cauda equina?
lessened risk of direct cord injury when a needle is placed into this space
where is the epidural space located?
posterior to the dura and anterior to the ligamentum flavum
contraindications to a central block (5)
- infection at the site of injection or near CNS
- coagulopathy or use of anticoagulants
- neuromuscular disease
- cardiac frailty
- patient consent & ability to tolerate procedure
when placing an epidural, how do you know that the needle is passing through the ligamentum flavum and enters the epidural space?
a sudden loss of resistance to injection of air or saline
how do you know that your spinal is in the correct place (subarachnoid space)?
freely flowing CSF
what is the principal site of action for neuraxial blockade?
(M&M)
believed to be the nerve root, at least during initial onset of block
what is the 1st ligament encountered when inserting the needle for a central block?
supraspinous ligament
what is the most internal ligament that is immediately posterior to the epidural space?
ligamentum flavum
2 approaches to place a central block
midline
paramedian
why is the epidural considered a “potential space”?
it’s a collapsed structure like an uninflated balloon or esophagus
what is contained in the epidural space?
nerves, vessels, and fat where roots pass outwardly
if using the midline approach, how deep to the skin is the epidural space generally?
5 cm
what borders the epidural space?
epidural veins
why are central blocks contraindicated in a pt with MS?
effects of LA on cord
if necessary, epidural would be better than a spinal
cardiac diseases that are absolute contraindications for central blocks
why?
outflow obstructions: aortic stenosis, HOCM, IHSS
SVR specific BP regulation, sympathectomy can result in cardiac arrest with difficulty resuscitating (TC said when they die they die 4real)
what lab might you want to get in a pt on aspirin needing a central block?
TEG - tests platelet function
ASRA recommendations for INR level prior to neuraxial block
(article)
“normal”
< 1.5
s/s that warrant immediate evaluation after central block
- altered pain, temp, or motor function
- changes in bowel or bladder function
- severe back pain
what is a “total” spinal?
injected meds block nerves high into the thoracic or even cervical levels
results in SNS blockade → bradycardia, hypotension, vascular collapse, apnea, LOC
interventions you should expect to do after you realized you just gave your pt a total spinal (oopsies)
manage airway
manage CV collapse (pressors, fluids)
adverse or exaggerated physiological responses assoc. with central blocks
(Table 45-6)
- urinary retention
- high block
- total spinal
- cardiac arrest
- anterior spinal artery syndrome
- Horner syndrome
what is Horner syndrome?
- unilateral sympathetic chain blockade
- more assoc. with peripheral blocks
- clinically looks like a stroke
- resolves when block wears off
complications of central blockade related to needle/catheter placement
(Table 45-6)
- backache
- dural puncture/leak - PDPH, diplopia, tinnitus
- neural injury
- bleeding
- misplacement (vascular injection, spinal, inadequate anesthesia)
- catheter shearing/retention
- inflammation
- infection
complications of central blocks r/t drug toxicity
(Table 45-6)
- systemic LA toxicity
- TNS
- cauda equina syndrome
what causes a PDPH (“spinal headache”)?
what techniques can cause it?
dural puncture occurs and dural closure is inadequate, resulting in CSF leakage
large needle, multiple attempts
classic symptoms of a spinal headache (PDPH)
headache that’s worse in upright position and relieved when supine
conservative treatment of spinal headache
rest, supine position, caffeine, hydration
management of a spinal headache if conservative measures fail
blood patch (20 mL blood used to “patch” dura)
should relieve within an hour or 2
why is a stylet used in a spinal block?
reduces likelihood of coring tissue during insertion
what is the purpose of non-cutting needles for spinal block?
cone-shaped tip designed to separate without cutting tissues
what is baricity?
- LA density relative to the density of CSF
- reflects the response of the injected LA to native CSF
isobaric solution
tends to stay in the same location
what is a hyperbaric solution?
- denser, heavier than CSF
- “sinks”
- tend to move to the most dependent area of the spine (T4-T8 in supine position)
what happens when a hyperbaric LA solution is injected and the pt is in a head-down position?
(book)
solution spreads cephalad
what happens when a hyperbaric solution is given and the patient is put in a lateral position?
(book)
greater effect on dependent (down) side
common additive to make a solution hyperbaric
7.5% dextrose
(typically pre-mixed as hyperbaric bupivacaine)
of note, premixed hyperbaric bupivacaine has 8.25% dextrose in it
what is a hypobaric solution?
- less dense (lighter) than CSF
- “floats”
if you give a hypobaric LA solution and put the pt in a head-down position, where is the solution going to go?
(book)
caudad
effect of a hypobaric solution move when pt is in a lateral position
(book)
greater effect on nondependent (up) side
when might you use a hypobaric spinal?
to affect the left hip while lying on the right
most important factors affecting the spread of spinal anesthesia
(table 45.2)
- baricity of solution
- position of patient during and immediately after injection
- drug dosage
- site of injection
“other” factors affecting dermatomal spread of spinal anesthesia
(table 45.2)
- age
- CSF
- curvature of spine/spinal stenosis
- drug volume
- intraabdominal pressure
- needle direction
- patient height
- pregnancy
advantages of using the midline approach over the paramedian approach
- fewer angles
- approach structures directly
- offers widest portion of epidural space
adverse effect of sympathetic blockade with central block
loss of vascular tone/SVR → hypotension
how quickly will you see “sympathectomy” with spinal block?
how can you prevent this?
within minutes of injection
small doses of pressors, volume challenge (in eligible pts)
what dermatome levels block cardioaccelerator nerves?
T1-T4
adverse effect of cardioaccelarator nerve blockade
- prominent, unopposed PNS stimulation (bradycardia)
- may have profound hypotension, LOC
adverse effect of neosynephrine for hypotension assoc. with sympathetic blockade
reflex bradycardia may result in asystole with a high-level spinal
most prominent cervical spinous process
C7
mL per dermatome initial dosing for lumbar epidural
(worksheet)
1-2 mL per segment (depending on pt height)
dermatome that corresponds with the base of the scapula
T7
dermatome that corresponds to the umbilicus
T10
dermatome level that corresponds with the superior aspect of the iliac crests
L4
how can blockade height be manipulated
by adjusting height and position at insertion
bupivacaine dosing to block perineum & lower limbs (via spinal)
(table 45-4)
4-10 mg
bupivacaine dose to block lower abdomen (via spinal)
(table 45-4)
is that what this means? sos
12-14 mg
bupivacaine dose to block upper abdomen (via spinal)
(table 45-4)
12-18 mg
how long does 0.75% bupivacaine in 8.25% dextrose last via spinal?
90-120 min
how long does 0.75% bupivacaine in 8.25% dextrose + epi last via spinal?
100-150 min
(1.5-2.5 hrs)
advantages of epidural vs spinal?
- ability to create sensory blockade without motor blockade
- can titrate dosage to change spread and clinical effect
- can provide prolonged effect
- less dense motor block
disadvantages of epidural vs. spinal
larger needle placement =
- increased risk of bleeding from inadvertent vessel injury
- increased risk spinal headache if inadvertent subarachnoid puncture
disadvantages of epidural vs. spinal
larger needle placement =
- increased risk of bleeding from inadvertent vessel injury
- increased risk spinal headache if inadvertent subarachnoid puncture
how is clinical effect of an epidural acheived?
through both action on spinal roots as they pass through the epidural space and diffusion into CSF (where action is on spinal cord)
tell me about the needle used for an epidural catheter placement
special needle that’s both blunted and curved
what is the purpose of a blunted curved needle for access to epidural space for catheter placement?
- blunting decreases likelihood of dural puncture
- curvature protects dura by avoiding a piercing tip on the distal end
2 techniques used to identify the epidural space
- loss of resistance
- hanging drop (using saline)
what should you do if attempting to place an epidural catheter and you realize you’ve punctured the dura?
remove the needle and the catheter (if placed already)
do not withdraw the catheter from the needle - if the catheter must be withdrawn, remove the needle then the catheter
test dose used for an epidural
3ml 1.5% lidocaine with 1:200,000 epi
(45 mg lidocaine, 15 mcg epi)
effect of a higher concentration agent with less volume
greater density with less spread
effect of a lower concentration agent with more volume
more diffuse but less intense blockade
mL needed to block T10 to S5
12 mL
does redosing of an epidural catheter require an additional test dose?
no, but should always be aspirated first
if you’re trying to place an epidural but you lose resistance and see CSF when you remove the stylet, what should you do?
remove the needle, move up a level, try again :(
2% chloroprocaine:
onset?
sensory block?
motor block?
- onset - fast
- sensory - analgesic
- motor - mild to moderate
3% chloroprocaine:
onset?
sensory block?
motor block?
- onset: fast
- sensory: dense
- motor: dense
≤ 1% lidocaine:
onset?
sensory block?
motor block?
- onset: intermediate
- sensory: analgesic
- motor: minimal
1.5% lidocaine:
onset?
sensory block?
motor block?
onset: intermediate
sensory: dense
motor: mild to moderate
2% lidocaine:
onset?
sensory block?
motor block?
- onset: intermediate
- sensory: dense
- motor: dense
1% mepivacaine:
onset?
sensory block?
motor block?
onset: intermediate
sensory: analgesic
motor: minimal
2-3% mepivacaine:
onset?
sensory block?
motor block?
- onset: intermediate
- sensory: dense
- motor: dense
≤ 0.25% bupivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: analgesic
- motor: minimal
0.5% bupivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: dense
- motor: mild to moderate
0.75% bupivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: dense
- motor: moderate to dense
0.2% ropivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: analgesic
- motor: minimal
0.5% ropivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: dense
- motor: mild to moderate
0.75% - 1% ropivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: dense
- motor: moderate to dense
if you’re trying to remove an epidural catheter and it won’t come out (yikes) what should you do?
put pt in placement position - may open spaces sufficiently to withdraw the catheter
concentration of epidural lidocaine for sensory block
motor/surgical block?
- sensory: ≤ 1%
- motor: 2%
concentration of epidural bupivacaine for a sensory vs. motor/surgical block
- sensory: ≤ 0.25%
- motor: 0.5%
*if he tries to get tricky, 0.75% best for motor but apparently unavailable
concentration of epidural ropivacaine for a sensory block
0.2%
concentration of chloroprocaine for a motor/surgical block
3%
- C5
- T10
- L2
- L3
- L5
A. C6
B. C7
C. C8
D. T1
E. T2
A. C5
B. C6
C. S2
D. S1
0.5% ropivacaine:
onset?
sensory block?
motor block?
- onset: slow
- sensory: dense
- motor: mild to moderate
Which neuraxial dose of opioids is similar to IV dosing?
Epidural
Subarachnoid dosing of opoids is about ______% of IV dosing
10-20%
