Neuraxial Anesthesia: A Review Flashcards
which interspace is tuffiers line
L4-L5
where does the spinal cord end
L1/L2
what is the target for the spinal and the epidural
nerve roots
anatomical considerations for the parturient
engorged epidural veins, makes dura small and creates exaggerated spread during spinal administration
what is the solution mixed with an epidural always
normal saline
spinal: what does it depend on (4 most important factors)
dosage, baricity, patient positioning, site of injection
what kind of block is an epidural/what does it depend on?
the volume of LA which determines the dermatome level
absolute contraindications to neuraxial anesthesia
patient refusal increased ICP severe aortic or mitral valve stenosis * coagulopathy or bleeding diathesis severe hypovolemia infection at injection site
aortic valve stenosis: mild. jet velocity (m/sec), mean gradient (mmHg), valve area (cm^2)
jet velocity (m/sec) <3 mean gradient (mmHg) <25 valve area (cm^2) >1.5
aortic valve stenosis: moderate. jet velocity (m/sec), mean gradient (mmHg), valve area (cm^2)
jet velocity (m/sec) 3-4 mean gradient (mmHg) 25-50 valve area (cm^2) 1-1.5
aortic valve stenosis: severe. jet velocity (m/sec), mean gradient (mmHg), valve area (cm^2)
jet velocity (m/sec) >4 mean gradient (mmHg) >50 valve area (cm^2) <1
aortic valve stenosis: critical. jet velocity (m/sec), mean gradient (mmHg), valve area (cm^2)
jet velocity (m/sec) >5 mean gradient (mmHg) >80 valve area (cm^2) < .7
relative contraindications to neuraxial anesthesia (7)
uncooperative patient LA allergy (esters >amide) patient on anticoagulant or thrombolytic therapy preexisting neurologic deficit chronic headache or backache severe spinal deformity valvular stenosis
informed consent: document the following
advantages and disadvantages
block appropriate for procedure but not guaranteed
risks and benefits
ensure patient understands
allow patient to ask questions
do not attempt to dissuade from general if already agreed to
consider having these two things started before spinal administration
bolus and phenylephrine infusion
at minimum, monitor these things during neuraxial administration
peripheral IV patency suction airway sypplies EKG, BP, pulse ox, possibly O2 supportive meds (induction agent, paralytic, atropine, vasoactive medication)
how to create larger interspinous spaces
aside from angry cat or shrimp position, have them push against your thumb
prior to starting procedure, verify
patent IV
monitoring devices, oxygen attached and functioning
resuscitation equipment available
what is the most commonly used interspace for a spinal
L3-L4
describe a touhy needle used for epidurals
pronounced curve
blunt tip
easier for novices
directional placement of catheter
describe a crawford needle used for epidurals
not curved
easier to insert
higher rate of dural punctures
for an epidural, distance to ligamentum flavum varies with
body habitus
level of plcement
standard depth of ligamentum flavum
4-6cm
does an epidural needle require an introducer
no, theyre larger more rigid needles
describe the bromage grip for epidural placement
hand firm support to stabilize needle
attach and secure syringe
passing catheter through needle
name ligaments in order to dura
supraspinous interspinous ligamentum flavum epidural space dura
what happens if you see a small amount of clear fluid during epidural placement
CSF would be a copious amount, so a small amount is ok
how many gauges smaller than the epidural needle is the epidural catheter
typically two gauges smaller than a needle
what happens if paresthesias occur during catheter placement
stop. if it isn’t persistent, its ok to keep going. theyre not uncommon
how far do you advance the epidural catheter
3-5cm past the needle hub
shallow placement of epidural catheter may result in
dislodgment of epidural space
too deep placement of epidural catheter may result in
puncture of dura
passage into epidural vein
migration through intervertebral foamen
test dose for epidural?
first, aspirate
1.5% lidocaine and 1:200,000 epinephrine
inject 3mL which is 45mg lidocaine and 15mcg epinephrine
if needle is in intravascular space during epidural test dose, what do you anticipate seeing
increase in HR and BP
what is in hyperbaric solution for a spinal
dextrose
what is in hypobaric solution for a spinal
sterile water
other factors related to spinal level (not the most important 4) include
patient height pregnancy age CSF volume curvature of the spine volume intra abdominal pressure needle direction
what is the most dependent area of the spine that hyperbaric solutions mitigate to
T4-T8
spinal needles that are not cutting needles (3)
whitacre, sprotte, pencan
how to utilize a cutting needle to minimize frequency of PDPH
rotate it 90 degrees, separates dura a little more and cuts a little less
what are the two pops felt during a spinal
ligamentum flavum
dura
how to do a continuous spinal (and why)
provides prolonged surgical anesthesia and postoperative pain management
dura punctured 17 gauge epidural needle
epidural catheter passed through dura than subarachnoid space
when to consider a continuous spinal
consider when a wet tap occurs during epidural placement
describe a two level CSE
spinal placed first
epidural catheter placed 1-2 levels above
describe a one level CSE
placement of epidural needle
spinal needle passed through
small intrathecal dose injected (opioid or smaller dose of LA)
epidural catheter placed
goal of CSE
relieve pain so mom can deliver
additional concerns of CSE include (3)
intrathecal opioid effects on fetus
inability to ambulate after receiving narcotics
maternal hypotension and itching
potential complications of CSE include (6)
failure to obtain either intrathecal or epidural block catheter migration increased spinal level metallic particles PDPH neurologic injury
if you use the paramedian approach for a spinal, which ligaments do you not go through
the supraspinous and interspinous ligament
if youre hitting bone early during insertion of spinal,
you are touching the superior crest of spinous process below the interspace. redirect cephalad
if youre hitting bone late during insertion of a spinal,
needle is touching the inferior surface of the spinous process above the interspace. redirect caudal
if paresthesia does not resolve during insertion of spinal
remove and reposition
if you get frank blood during insertion of a spinal, you are likely in
an epidural vein. withdrawal and reposition
if you get blood tinged CSF during placement of a spinal,
allow CSF to flow for several seconds. when clear, inject medication
does LA metabolize in CSF
no, this is based on rate of absorption into systemic vasculature.
what will addition of vasoconstrictors to neuraxial anesthesia do
slow absorption and prolong block
esters include (3)
procaine, chlorprocaine, tetracaine
amides include (4)
lidocaine, mepivicaine, ropivicaine, bupivicaine
procaine: pKa, percent ionized, percent protein binding, onset, DOA
pKa 8.9 percent ionized 97 percent protein binding 6 onset slow DOA 60-90 minutes
chlorprocaine onset, DOA
onset fast
DOA 30-60 minutes
tetracaine pKa, percent ionized, percent protein binding, onset, DOA
pKa 8.5 percent ionized 93 percent protein binding 94 onset slow DOA 180-600
lidocaine pKa, percent ionized, percent protein binding, onset, DOA
pKa 7.9 percent ionized 76 percent protein binding 64 onset fast DOA 90-120
mepivicaine onset, DOA
fast, 120-240
ropivicaine onset, DOA
slow, 180-600
bupivicaine pKa, percent ionized, percent protein binding, onset, DOA
pKa 8.1 percent ionized 83 percent protein binding 95 onset slow DOA 180-600
neuraxial additives: epinephrine
MOA
dose
greater effect with
alpha 1 agonist
.1-.2mL of 1:1000 solution can be added to LA’s
greater effect with tetracaine
neuraxial additives: phenylephrine MOA, dose, greatest effect with?
pure alpha agonist slightly more effective than epinephrine
.05-.2mL of 1% solution (.5-2mcg added to LA)
greatest effect with tetracaine
neuraxial additives: clonidine MOA contraindicated with? synergistic with helps with
selective alpha 2 agonist
used when epinephrine is contraindicated
when mixed with lidocaine or bupivicaine, has synergistic effects
the central action appears to help with tourniquet pain
most common neuraxial additives include
fentanyl
morphine
fentanyl as a spinal additive: solubility
high lipid solubility. binds directly to lipid elements of spinal cord. less drug available to diffuse systemically.
fentanyl as a spinal additive: dosage, onset, DOA
provides profound analgesia
12.5-25mcg mixed with LA
onset: 5-10 minutes
DOA: 2-4 hours
morphine as a neuraxial additive (spinal OR epidural): solubility
highly polarized, not very lipid soluble
drifts freely in CSF
in approx 6-8 hours, will rise to respiratory center
morphine as a neuraxial additive (spinal OR epidural): dosage, onset, DOA
provides profound analgesia
.1-.25mg mixed with LA
onset 60-90 minutes
DOA approx 24h
morphine as a neuraxial additive (spinal OR epidural): adverse effects (3)
itching
urinary retention
delayed respiratory depression
dexmedetomidine as a neuraxial additive: dosing
spinal: 5mcg
epidural: 20-50mcg
dexmedetomidine as a neuraxial additive: side effects
profound hypotension (when used in conjunction with an opioid ex: precedex and fentanyl) prolonged block
which fibers are blocked first for neuraxial anesthesia
sympathectomy: 1st, preganglionic B fibers. vasodilation=good block aka drop in BP first sign. n/v may follow
fiber type: A alpha
function, diameter, myelination, block onset
proprioception
6-22
heavy
last
fiber type: A beta
function, diameter, myelination, block onset
touch, pressure
6-22micrometers
heavy
intermediate
fiber type: A gamma
function, diameter, myelination, block onset
muscle tone
3-6
heavy
intermediate
fiber type: A delta
function, diameter, myelination, block onset
pain, cold, temperature, touch
1-5
heavy
intermediate
fiber type: B
function, diameter, myelination, block onset
preganglionic autonomic vasomotor
<3
light myelination
early block onset
fiber type: C sympathetic
function, diameter, myelination, block onset
postganglionic vasomotor
.3-1.3
no myelination
early onset
fiber type: C dorsal root
function, diameter, myelination, block onset
pain, warm and cold temperature, touch
.4-1.2
no myelination
early block onset
which fibers follow B fibers and what is the result
a delta and C pain fibers and temperature follow B fibers.
unable to discriminate light touch or temeprature
temperature discrimination mirrors sensory loss
which are the last fibers to be blocked and what is the result
A alpha beta and gamma
touch and proprioception, surgical muscle relaxation, may feel pressure
what are the goal nerve fibers for a labor epidural
a delta and C fibers so she can still feel contractions
evaluation of block
assess block q2-3 minutes
frequent assessment of BP and VS
physiologic changes closely resemble block level
which dermatome level do you need for labor analgesia
T10
which dermatome level do you need for a C section
T4-T6
autonomic blockade is where in relation to sensory block? motor blockade is where in relation to sensory block?
autonomic blockade is usually two dermatomes higher than the sensory block
motor blockade is usually two dermatomes lower than the sensory block
complications to neuraxial anesthesia
HoTN intercostal muscle paralysis apnea/phrenic nerve paralysis paresthesia subarachnoid or epidural hematoma meningitis/epidural abscess chemical meningitis n/v PDPH
what may a patient complain about when having a PDPH
if i lay down i feel fine, if i sit up I have a HA
risk factors for PDPH include
patient needle size and type patient population (young, female, pregnancy)
s/sx of PDPH
bilateral frontal or rtetroorbital or occipital extends into next photophobia nausea positional
PDPH treatment in first 12-24 hours (conservative)
recumbent position analgesics fluid administation caffeine stool softeners and soft diet
epidural blood patch for PDPH includes
injecting 15-20mL autologous blood
below initial puncture site by 1-2 levels
90% will respond to initial therapy
