MM Ch 45 Flashcards
Placement to avoid potential needle trauma to the spinal cord
lumbar (subarachnoid) spinal puncture
adult: below L1
child: below L3
The principal site of action for neuraxial blockade is
nerve root
at least during initial onset
produces the sympathetic blockade seen in a neuraxial block
Interruption of efferent autonomic transmission at the spinal nerve roots
Neuraxial blocks
expected V/S fx
↓ BP
↓ in heart rate
Deleterious CV effects should be anticipated
T/F
In a normotensive pt, preloading with a fluid bolus does not prevent hypoTN
True
volume loading IVF 10 to 20 mL/kg in a healthy patient before of the block repeatedly fails to prevent hypotension (in the absence of preexisting hypovolemia).
Excessive or symptomatic bradycardia should be treated with
atropine
⭐️
Major contraindications to neuraxial anesthesia
lack of consent
coagulation issues
severe hypovolemia
elevated ICP
infection injxn site
Epidural vs Spinal
Needle insertion
epidural:
sudden loss of resistance (to injection of air or saline) as the needle passes through the ligamentum flavum and enters the epidural space
spinal:
advanced thru epidural space & penetrate the dura–subarachnoid membranes, as signaled by freely flowing cerebrospinal fluid
Where can an epidural block can be performed?
at the lumbar, thoracic, or cervical level
Epidural technique uses
surgical anesthesia
OB analgesia
Postop pain
chronic pain
Epidural vs spinal
onset
Epidural anesthesia is slower (10–20 min)
Intrathecal
injection into the spinal canal, or into the subarachnoid space
Spinal aneshesia
AKA….
spinal block
subarachnoid block
intradural block
intrathecal block
More volume of LA is needed for (epidural/spinal) block.
epidural
Neuraxial anesthesia
collective term for spinal, caudal, and
epidural anesthesia
Cesarean delivery is most commonly performed under spinal or epidural anesthesia d/t..
Both blocks allow a mother
to remain awake and experience the birth of her child
vertebral bones
7 cervical (C)
12 thoracic (T)
5 lumbar (L)
sacrum: fusion of 5 sacral (S) vertebrae,
small rudimentary coccygeal vertebrae
Cauda Equina location
All 12 thoracic vertebrae articulate with
their corresponding ribs
location in which the spinal cord and its coverings sit
spinal canal
vertebral bodies & intervertebral disks
anterior and posterior support
anteriorly:
anterior & posterior longitudinal ligaments
posteriorly:
ligamentum flavum
interspinous ligament
supraspinous ligament
midline approach
a needle passes through:
1) these three dorsal ligaments:
ligamentum flavum
interspinous ligament
supraspinous ligament
2) through an oval space between the bony lamina and spinous processes of adjacent vertebrae
spinal canal contains
Spinal cord & its coverings (the meninges)
fatty tissue
a venous plexus
The ___ mater is adherent to the spinal cord.
The arachnoid mater is usually adherent to the thicker and denser __ mater.
pia
dura
Cerebrospinal fluid (CSF) is contained…
between the pia and arachnoid maters in the subarachnoid space.
subdural space
generally a poorly demarcated, potential space that exists between the dura and arachnoid membranes
epidural space
better-defined potential space bounded by the dura and the ligamentum flavum
spinal cord normally extends from ___ to the ___ in adults ( ___ in children)
the foramen magnum
level of L1
L3
Damage to the cauda equina
unlikely
nerve roots float in the dural sac below L1
tend to be pushed away (rather than pierced) by an advancing needle.
Nerve blocks close to the ___ carry a risk of subdural or subarachnoid injection
intervertebral foramen
Spinal block inject LA into ___.
Epidural block injects LA into ___.
spinal = CSF, subarachnoid space
epidural = epidural space
Injxn Site
epidural
midpoint of the dermatomes that must be anesthetized
Blockade of neural transmission in
posterior nerve root fibers
vs
anterior nerve root fibers
posterior: interrupts somatic and visceral sensation
anterior: prevents efferent motor and autonomic outflow
Neuraxial blocks provide excellent operating conditions by (2)
interrupting afferent transmission of painful stimuli
abolishing efferent impulses for skeletal muscle tone
Sensory blockade interrupts (2)
somatic and visceral painful stimuli
somatic stimuli: light touch, vibration, pressure, cutaneous tension
What characteristics make a fiber easier to block
Smaller
myelinated
Differential blockade
LA [ ] decreases further from the level of injection
sympathetic blockade (judged by temperature sensitivity) may be 2+ segments more cephalad than the sensory block (pain, light touch)
sensory block ~several segments more cephalad than the motor blockade.
(AUTONOMIC BLOCKADE)
what produces sympathetic blockade?
interruption of efferent autonomic transmission at the spinal nerve roots during neuraxial blocks
Sympathetic outflow
vs
parasympathetic outflow
SNS = thoracolumbar
PNS = craniosacral
Neuraxial anesthesia does not block the _____. This means…
vagus nerve (tenth cranial nerve)
response to block result from:
↓ sympathetic tone
and/or
unopposed parasympathetic tone
Cardiovascular Manifestations
varying ↓BP
possible ↓HR
(more cephalad dermatomal levels & extensive sympathectomy)
T5 to L1 block:
viscera and lower extremity blood pooling
Arterial vasodilation
arterial vasodilation may be minimized by…
compensatory vasoconstriction above the level of the block
ex: lower thoracic dermatome block
high sympathetic block
CV fx
prevents compensatory vasoconstriction
block sympathetic 🩷 accelerator fibers (T1 to T4)
Unopposed vagal tone a/w spinal anesthesia
(occasional)
sudden bradycardia
complete heart block
cardiac arrest
How can we position OB in 3rd trimester to minimize obstruction of venous return?
Left uterine displacement
Autotransfusion
placing the patient in a head-down position
hypoTN measure
HypoTN d/t block
interventions
Autotransfusion: head-down position
IVF bolus 5–10 mL/kg
Phenylephrine preferred for OB
GI fx
decrease hepatic flow (d/t decreased MAP)
faster return of GI fxn after open abd Sx
(use minimal opioid with the block)
GU fx
little renal effect if BP normal
urinary retention until block wears off
no foley = use shortest acting possible
hx of retention = assess bladder distention
Metabolic & Endocrine fx
Surgery = neuroendocrine stress response
HTN
tachy <3
hyperglycemia
protein catabolism
↓ immune response
altered renal function
LA can suppress/block this
admin before incision and continue postop
Indications
used alone or in conjunction with general anesthesia for many procedures below the neck
lower abdominal, inguinal, urogenital, rectal, and lower extremity surgery
Relative c/a
Upper abd Sx with neuroaxial (NA) block
difficult to safely achieve a sensory level adequate for patient comfort
less commonly used
preexisting neurological deficits or demyelinating diseases
may report worsening symptoms following a neuraxial block
may not be able to tell if it was the block or Dz
document existing deficits
warfarin use
normal PT & INR documented prior to the block, unless the drug has been discontinued for weeks
Rivaroxaban (Xarelto) use
discontinued 72 hours before block
if earlier, can order anti-factor Xa but no values have been established
remove catheter 6 H before postop dose
if dosed before removal, wait ~24 H
Apixaban (Eliquis) use
same as Xarelto but wait 26-30 H to remove cath if dosed before removal
Stop Plavix use how long before NA block
5 to 7 days
By themselves, ….. do not increase the risk of spinal hematoma from neuraxial anesthesia procedures or epidural catheter removal
aspirin and other (NSAIDs)
Heparin use
Avoid NA block: if on therap dose + ↑PTT
Low-dose SQ prophylaxis not a contraindication to block or removal
block/removal 4 to 6 h after dosing with 5000 units
Intra op Heparin:
block 1 H before dose
d/c 1 h before or 2 to 4h after subsequent heparin dosing
No set guidelines, but ___ & ___ blocks are best done while the patient is awake to warn us of toxicity SEs.
thoracic and cervical
In this position, CSF
will not freely flow through the needle, so subarachnoid placement must be confirmed by CSF aspiration.
Jackknife
Midline approach
Skin wheal using 25G
increase in tissue resistance
(supraspinous & interspinous ligaments)
an obvious increase in resistance (ligamentum flavum)
not deep & hit bone:
lower spinous process
deep & hit bone:
a) superior spinous process
b) lamina (too lateral)
Paramedian Approach
for those difficult to position (arthritis, spine issues)
skin wheal:
2 cm lateral to the inferior aspect of the superior spinous process of
the desired level
approach is lateral to most of the interspinous ligaments & penetrates the paraspinous muscles
deep & hit bone:
(lat lower lamina)
adjust slightly toward midline
Spinal Needles
tightly fitting, removable stylet completely occludes lumen to avoid tracking epithelial cells → subA space
blunt tip = less PDPH
sproutte: more vigorous CSF flow; ↑PDPH
(Spinals)
What are the two “pops” that are felt?
first: penetrate ligamentum flavum
second: penetration dura–arachnoid membrane
If free flow occurs initially but CSF cannot be aspirated after attaching the syringe…
the needle likely will have moved
Signs you need to adjust your spinal needle position
Persistent paresthesia or pain with injection of drugs
withdraw and redirect the needle
Factors Influencing Level of Spinal Block
most important:
-agent’s baricity
-pt position (during & immediately after injection)
-dosage
others:
level of injection
ptheight
vertebral column anatomy
age
spine curvature
IAbd pressure
pregnancy
drug volume
migration of the local anesthetic
cephalad in CSF depends on its
density relative to CSF (baricity)
CSF specific gravity: 1.003 - 1.008 at 37°C
CSF specific gravity
1.003 - 1.008 at 37°C
hyperbaric vs hypobaric
hyper = heavier/denser than CSF
hypo = lighter ‘ ‘
Positioning to manipulate LA migration using hyper/hypobaricity
head-up position:
hypobaric ↑ to head
hyperbaric settle ↓ to feet
lateral position:
hyperbaric affects dependent (down) side more
hypobaric to nondependent (up) side
How to make LA solution hyper/hypobaric
hyperbaric: add glucose
hypobaric: add sterile water or fentanyl
agents lacking glucose may be
mixed with CSF (at least 1:1) to make their solutions isobaric
this type of solution tends to
remain at the level of injection
isobaric
higher levels of anesthesia are
achieved if the injection is directed __ than if the point of injection is
oriented…
cephalad
laterally or caudad
Agents specific gravities
note: CSF is 1.003 - 1.008 at 37°C
T/F
↑ CSF volume = greater spread
False
decreased CSF volume = greater dermatomal spread
Only use these types of solutions for spinals
preservative-free local
anesthetic solutions
can add pressors, opioids, clonidine
“saddle block”
sitting position
keeping the patient sitting for 3 to 5 min following injection so
that only the lower lumbar nerves and sacral nerves are blocked
We would make the LA solutio (hyper/iso/hypo)baric for a fracture surgery.
Hypo & iso
so the pt doesn’t have to lay on the fractured side
The epidural space
anatomy
surrounds the dura mater posteriorly, laterally,
and anteriorly
Nerve roots travel here as they exit laterally via foramen and become P nerves
fatty connective tissue, lymphatics, & a rich venous (Batson) plexus
Epidural is (more/less) dense than Spinal.
What are the benefits?
less
relatively dilute LA [ ] + opioid
can provide analgesia w/o motor block
segmental block possible b/c can be confined close to level of injection
segmental block
epidural anesthesia
well-defined band of anesthesia at certain nerve roots, leaving nerve roots
above and below unblocked.
ie: thoracic epidural providing upper abdominal anesthesia while sparing cervical and lumbar nerve roots
Thoracic vs lumbar epidural
ease & risks
Thoracic:
can be harder d/t more overlap of spinous processes
higher risk accidental dural puncture
How do epidural catheters affect postop ventilation requirements?
prolonged durations of analgesia
may obviate or shorten postop ventilation in pts w underlying lung Dz and following chest surgery
Epidural needles
17 to 18 gauge, 3 or 3.5 inches
Tuohy:
blunt, curved tip pushes dura away after passing through the ligamentum flavum w/o penetrating it
straight = ↑ risk dural puncture
Epidural catheter
needles
19- or 20-G catheter
introduced thru 17- or 18-G epidural needle
advance catheter 2 to 6 cm into the epidural space
too little: risk dislodgement
too far: unilateral block or penetrate epidural vein
T/F
Test doses can only detect accidental
intravascular injection
False
Can detect both subarachnoid and
intravascular injection
Test Dose
LA + epi
typically 3 mL of 1.5% lido + 1:200,000 epi
(0.005 mg/mL)
45 mg lido if injected intrathecally, will
produce spinal anesthesia that should be rapidly apparent
T/F
aspirating prior to injection rules out/confirms accidental intravenous injection
False
Simply aspirating prior to injection is insufficient to avoid accidental intravenous injection
false-negative aspirations
possible w/ both a needle and a catheter
Using epi as test dose
not ideal
False positives
(uterine contraction: pain or ↑ HR coincident to test dosing)
false negatives
(brady🩷 & exaggerated ↑TN in response to epi in patients taking β-blockers)
⭐️
LA intravascular injection S/S
tinnitus
metallic taste
slurred speech
altered mentation
Incremental dosing
(“each dose is a test dose”)
very effective to r/o accidental IV injxn
avoids serious complications
- aspiration negative
- inject a fraction of the dose (5 ml)
large enough to produce mild symptoms/signs
small enough to avoid seizures or CV compromise
Epidurals
Ways to prevent systemic toxic SEs & accidental intrathecal injection
use an initial test dose
aspirate prior to each injection
always use incremental dosing
(“each dose is a test dose”)
⭐️
You did an epidural block & local anesthetic systemic toxicity is now occurring. What do you do?
Rescue lipid emulsion
(20% Intralipid 1.5 mL/kg)
followed by a 0.25-mL/kg infusion
What pt factors affect epidrual dose requirement?
decreases with age (↓ epidural sapce size/compliance)
height affects extent of cephalad spread
taller = more mL per segment
❌ weight
Chloroprocaine
considerations
ester
rapid onset
short duration
extremely low systemic toxicity
may interfere w/ analgesic fx of epidural opioids
bupivacaine vs ropivacaine
which produces less motor block w/ satisfactory sensory block?
ropivacaine
Local anesthetic solutions have a ___ pH for chemical stability and bacteriostasis.
acidic
w/ epi = even more acidic
LAs are ____ & exist primarily in the ionic form in commercial preparation.
weak bases
preparation = acidic
How do we get a faster onset of commercially prepared LA?
When do we not want to do this?
Increase the pH
add sodium bicarb (1 mEq/10 mL of local anesthetic) immediately before use
typically not added to bupivacaine, which precipitates above a pH of 6.8.
Spinal vs Epidural
onset
ease
predicatability
spinal:
-endpoint more clear (free-flowing CSF)
-onset is very fast
-technique has a very high success rate
epidural:
-dependent on the detection of a more
subjective loss of resistance (or hanging drop)
-onset slower
-more variable anatomy (epidural space)
-less predictable spread
Epidural Issues:
unilateral block
catheter either exited epidural space or went laterally
esp if threading catheter longer
withdrawing catheter 1 to 2 cm
reinject with pt placed unblocked side down
NA complications
Adverse/exaggerated phys responses:
Urinary retention
High block
Total spinal anesthesia
Cardiac arrest
Anterior spinal artery syndrome
Horner syndrome
d/t needle/catheter placement:
Backache
Dural puncture/leak
Postdural puncture headache
Diplopia
Tinnitus
Neural injury
Nerve root damage
Spinal cord damage
Cauda equina syndrome
Bleeding
Intraspinal/epidural hematoma
Misplacement
No effect/inadequate anesthesia
Subdural block
Inadvertent subarachnoid block
Inadvertent intravascular injection
Catheter shearing/retention
Inflammation
Arachnoiditis
Infection
Meningitis
Epidural abscess
Drug toxicity:
Systemic local anesthetic toxicity
Transient neurological symptoms
Cauda equina syndrome
Spinal anesthesia ascending into the cervical levels causes
severe hypotension, bradycardia, and respiratory insufficiency
“total spinal”
block extends to cranial nerves
accidental intrathecal injection
T/F
LAST is more of a concern with epidurals.
True
LAST is seen after epidural and caudal (but not spinal) blocks.
dose for spinal anesthesia is relatively small
Lipid emulsion for LAST rescue
MoA
reservoir in the blood to collect and transfer LA away from the heart and brain
Epi dosing in LAST
Incremental 1-mcg/kg doses rather than larger 10-mcg/kg doses
cardiac fxn not restored:
additional lipid emulsion up to
10 mL/kg.
LA toxicity comparison
(potency matches ability to cause toxic SEs)
Chloroprocaine: low potency; rapid metab
lidocaine & mepivacaine: intermediate in
potency and toxicity
most potent & toxic:
levobupivacaine, ropivacaine, bupivacaine,
tetracaine
Why is accidental intrathecal admin bad?
epidural & caudal anesthesia dose
is 5 to 10 times that required for spinal anesthesia
Subdural Injection
if epidural dose:
worse outcome
looks like “high spinal” (extends intracranially)
but
onset delayed ~15-30 min & “patchy” block
spinal subdural space
potential space between dura &
arachnoid
extends intracranially, so LA injected here can ascend to higher levels than when injected into the epidural space
Backache
usually benign
but can be part of serious complications, such as epidural hematoma and abscess
Postdural Puncture Headache (PDPH)
if needle enters subarach space
may be the result of just the tip of the needle scratching through the dura
bilateral, frontal, retroorbital, or occipital and extends into the neck
photophobia and nausea
Traction on CNs = possible diplopia
hallmark of PDPH
its association with body position
aggravated by sitting or standing
decreased by lying flat
PDPH is believed to result from
leakage of CSF from a dural defect and
subsequent intracranial hypotension
PDPH greatest risk scenario
accidental dural puncture with a large
epidural needle in a young pregnant woman
PDPH Tx
recumbent positioning
analgesics
hydration (IV, PO)
caffeine
hydration and caffeine stimulate CSF prodxn
epidural blood patch
epidural blood patch
15 to 20 mL autologous blood into the
epidural space at, or one interspace below puncture
stop further leakage of CSF by either mass effect or coagulation
Headache resolution is usually immediate and complete
PDPH diff dx
migraine
caffeine withdrawal
meningeal infection
subarachnoid hemorrhage
Neurological Injury
epidural hematoma or abscess
peripheral neuropathies
(some permanent)
sustained paresthesia during neuraxial
anesthesia/analgesia
redirect the needle
if the injection is associated with pain
immediately stop and withdraw needle
Direct injection into the spinal cord can
cause
paraplegia
Spinal or Epidural Hematoma
S/S
more sudden than epidural abscess
sharp back & leg pain with motor weakness &/or sphincter dysfunction
STAT MRI/CT
Epidural Abscess (EA)
Back pain & fever after epidural
Radicular pain or neurological deficit
4 stages
-back pain intensified by spine percussion
-nerve root or radicular pain
-motor/sensory deficits; sphincter dysfxn
-Paraplegia or paralysis
Epidural Abscess (EA)
interventions
remove catheter & culture tip
culture any site pus
blood Cx (staph aureus & epidermis)
MRI/CT
antiBX
decompression (laminectomy)
Epidural Abscess (EA)
prevention
-minimize catheter manipulation
-maintain closed system when possible
-micropore (0.22-μm) bacterial filter
-removing/exchange catheter, filter, & solution @ certain time intervals
Sheering of an Epidural Catheter
always withdraw catheter & needle together
Local Anesthetic Systemic Toxicity
Absorption of excessive amounts of LAs can produce toxic blood levels (“Intravascular Injection”)
rare if appropriate dose
transient neurological symptoms (TNS)
“transient radicular irritation (TRI)”
back pain radiating to the legs w/o sensory or motor deficits
after the resolution of spinal anesthesia & resolving spontaneously within several days
esp w/ hyperbaric lidocaine
Lidocaine & Mepivacaine
max doses
4.5 mg/kg
w/epi: 7 mg/kg
Lidocaine vs. Mepivacaine
uses
Both: infiltration, epidural, spinal, PN
Lido: IV regional, topical
Prilocaine max dose
8 mg/kg
Medium DoA agents
Prilo
Mepiv
Lido
short DoA agents
chloro + procaine
long DoA agents
Bupiv
Ropiv
Tetra
“BuRT”
Max dose of 3mg/kg
Cocaine
Tetracaine
Bupivacaine
Ropivacaine
CocTBuR
Chloroprocaine and Procaine
max dose
12 mg/kg
both short DoA
Procaine: S, I
Chloro: S, I, E, P
(S=spinal, I=infiltr8, E=epidurl, P=perip nerve)
