Considerations for epidural anesthesia Flashcards
What is an epidural anesthetic?
reversible chemical blockade of neuronal transmission produced by the injection of a local anesthetic into the epidural space to the region of the dural cuffs
An epidural anesthetic results in
temporary interruption of autonomic, sensory, and motor nerve fiber transmission related to drug concentration & volume
The danger with using hypobaric solution in a sitting position:
it can spread up & if it reaches cardioaccelerator fibers (T4, T5) then it can have hypotension & bradycardia
Describe the difference in volume administration for an epidural versus a spinal.
Need higher volume for an epidural because we are counting on diffusion
The onset for an epidural is
longer
The medication spread for an epidural is
diffusion dependent
The epidural anesthetic leaks into the
intravertebral foramen & paravertebral spaces
The advantages to epidural includes it reduces
surgical stress (thus opioid consumption)
possibly it decreases overall blood loss
risk of DVT
Advantages to epidurals include
it provides anesthesia and/or analgesia (can be titrated)- ability to re-dose with catheter) or convert from pain management to primary anesthetic (labor epidural)
-versatile- control extent of sensory & motor blockade, used wit or without adjunct medications
Every time you dose your epidural you must
always aspirate first & inject 5 cc max at a time
Disadvantages to epidural anesthesia include:
post dural puncture headache- large CSF leaks
sympathetic blockade occurs 100% of the time–> hypotension or bradycardia
block may last much longer than the procedure
urinary retention–> most common with spinal
regional takes “too much time”- more difficult than a spinal
Epidural selection is based upon:
surgeon expertise/preference- discuss case with surgeon, part of multimodal management in ERAS protocols
management of labor pain
procedures involving- abdomen & lower extremities
certain comorbidities- pulmonary disease
Absolute contraindications to epidurals include:
patient refusal
increased ICP
severe aortic or mitral valve stenosis (now more of a relative)
coagulopathy or bleeding diathesis
severe hypovolemia-> leads to hypotension
infection at the injection site
Relative contraindications to epidurals include:
local anesthetic allergy (more likely w/ esters)
patient on anticoagulant or thrombolytic therapy
preexisting neurologic deficit
chronic headache or backache
severe spinal deformity
valvular stenosis
uncooperative patient–> inability to communicate/obtain informed consent; unable to assist
Patients with these comorbidities may be a relative contraindication due to anticoagulant therapy:
atrial fibrillation
previous DVT
postsurgical administration- initiation of DVT prophylaxis
The preoperative patient assessment for the patient getting an epidural includes:
does patient understand proposed surgical technique
explain the spinal anesthetic and rational for preference
age considerations
never force or coerce a patient into any procedure
address any patient concerns–> some patients fear loss of control, reassure patient all appropriate medications will be administered
Documentation of informed consent includes:
advantages & disadvantages
block appropriate for procedure but not guaranteed
risks & benefits
ensure patient understands
allow patient to ask questions
do not attempt to dissuade from a general if already agreed to
Documentation does not exonerate you from
negligence!
When considering pre-procedure medication, considerations include:
reduce anxiety & provide some amnesia & analgesia- but do not over sedate
follow NPO standards for elective cases
consider bolus administration of IV solution
At a minimum prior to beginning epidural placement, have
peripheral IV, suction, airway supplies, ECG, blood pressure cuff, pulse oximeter–> possibly oxygen, supportive medications (induction agent, paralytic, atropine, vasoactive medication), support person
Describe the difference between spinal & epidural.
spinal- single shot (usually), dosage is less than epidural, baricity, patient position
epidural- catheter, volume block (isobaric medications because using volume to help with spread)
Describe the positions that can be used:
sitting, lateral decubitus, prone
Describe the needle approaches that can be used:
midline
paramedian–> ligamentum flavum will b the first you encounter (miss the other ligaments)
Placement options for the epidural include:
thoracic, lumbar, & caudal
In terms of positioning and landmarks, an assistant must
stand in front of the patient and not leave the patient
To position the patient correctly in the sitting position
hold a pillow or blanket or lean over table, drop their head down
roll their back- “angry cat” or “shrimp” position
When performing the lateral approach, it is important to
maintain midline positioning & limit spine rotation
Flexing the spine will create
larger interspinous space
need to optimize your positioning
Prior to starting the procedure, it is important to verify
patent IV
monitoring devices/oxygen attached & functioning
resuscitation equipment available
“walk” patient through the procedure
The procedure itself is
sterile
at a minimum, you must wear: a surgical hat, surgical mask, and sterile gloves
Prior to starting the sterile portion of the procedure, you should
palpate major landmarks- iliac crests & spinous processes of lumbar vertebrae
When deciding where to insert your epidural, you should
use the most identifiable interspace
L2-3 is the most common
examine one level above & below target
If processes are not palpable consider US
The site should be cleansed with
chlorhexidine gluconate & a sterile drape should be applied
Epidural needles are marked in
1 cm increments
standard needle is 9 cm
Describe the Tuohy needle.
pronounced curve, easier for novices, directional placement of catheter
Describe the Crawford needle
is not curved, easier to insert, higher rate of dural punctures
The hand position prior to needle insertion involves
straddling the selected interspace with the middle and index fingers of your non-dominant hand
raise a small intradermal skin wheal of local anesthetic with a 25-27 gauge needle
The distance to ligamentum flavum varies with
body habitus
level of placement- standard depth at lumbar level is 5 cm- depth within epidural space also varies
needle angle changes with level
Epidural needles are
larger and more rigid; do not require an introducer & provide better directional control
Describe the “bromage” grip.
hand firm support to stabilize needle
attach and secure syringe
passing catheter through needle
- the needle is placed with bevel cephalad
-advanced through supraspinous ligament & interspinous ligament
The alternative to the “Bromage” grip is to
attach and secure syringe
needle placed with bevel cephalad
hands stabilize needle on both sides
advanced through supraspinous ligament & interspinous ligament
Describe the loss of resistance method.
most common method
involves glass or plastic syringe filled with 2-3 mL of saline with air bubble
attach to epidural needle- resistance noted while needle is in ligament until epidural space is entered
tap on plunger with every movement
Describe the hanging drop method.
hub of epidural needle filled with saline until a small drop is visible
negative pressure created as needle passes into epidural space “sucks” drop in- more pronounced at thoracic levels
Once needle passes through the epidural space, an
immediate loss of resistance is noted
After loss of resistance is felt, the contents of the syringe are
injected into the epidural space
air (could give someone a pneumocephalus) vs. fluid (allows for dilation)
Epidural catheters are typically
two gauges smaller than needle
open-ended
multiport- lower incidence of inadequate analgesia & higher incidence of accidental vein cannulation
Markings help identify the depth of catheter placement described what the following indicate:
dashed lines
two-dashed lines
thick line
dashed lines- 1 cm
two-dashed lines= 10 cm
thick line= 12 cm
If paresthesia occurs
stop, withdraw slightly and redirect your needle
Describe how far the catheter should be advanced.
3-5 cm past the needle hub
Shallow placement of an epidural catheter will result in
dislodgement from the epidural space
Too deep of a placement of an epidural catheter will result in
puncture of dura
passage into epidural vein
migration through intervertebral foramen
Once you remove your needle, it is important to note the depth of the catheter at the skin. If the depth is
less than 1 cm to the epidural space, it needs to be replaced
You should NEVER attempt to
withdraw the catheter through the needle
it could result in catheter shear
Once the needle is safely removed:
attach adaptor to free end
look for presence of blood or CSF
“gently” aspirate
The test dose is
1.5% lidocaine with epinephrine 1:200,000
inject 3 mL- 45 mg lidocaine & 15 mcg of epinephrine
If you inject your needle and the test dose is administered in the subarachnoid space it becomes
a spinal
If you inject your needle and the test dose is administered in the intravascular space you will see
> 20% increase in HR & BP
To secure the catheter it should be
looped and taped away from midline- minimizes the chance of dislodgement & keeps off spinous processes
placed over shoulder
secure label to the end of the catheter
Describe the paramedian approach.
Useful when patient cannot flex spine-hx of previous spine surgery, RA or hip or upper leg trauma
skin wheal 1 cm lateral and 1 cm caudal to spinous process
Advance needle toward midline- needle passes through paraspinous muscles to ligamentum
The biggest difference with the paramedian approach includes:
it does NOT pass through supraspinous or interspinous ligaments
Trouble shooting can include
contacting bone, paresthesia, & blood in catheter
If you are contacting bone, you should
withdraw the needle and stylet to the subcutaneous fat. reposition the introducer and reinsert the needle
If the needle is touching the superior crest of spinous process below the interspace,
redirect cephalad
If the needles is touching the inferior surface of the spinous process above the interspace,
redirect caudal
If you repeatedly encounter bone,
remove the needle and reassess landmarks
If you see blood in the catheter,
withdrawal the catheter and replace it
If the patient experiences paresthesia during catheter insertion,
stop. if it resolves then can continue
if it is persistent- withdrawal and reposition
Caudal anesthesia is a
distal approach to the epidural space
Indications for a caudal approach includes
hemorrhoidectomy, chronic pain patients, & pediatric analgesia- inguinal herniorrhaphy, circumcision, perineal procedures
Describe the anatomy for the caudal approach.
technically difficult approach (especially in adults)- overall failure rate is 5%
more reliable in pediatrics
more difficult in adults due to variation in size, shape, and orientation of the sacral anatomy
The positioning for the caudal approach is
prone on a flexed table or with a pillow under the pelvis
legs spread and externally rotated
pediatrics- laterally positioned
For the caudal approach, care must be taken to ensure
not in subcutaneous
not in bone
Dosing for the caudal approach is
0.5-1 mL/kg body weight
varying LA concentrations
2.5 mg/kg body weight
When performing the caudal approach, you should
puncture the sacral hiatus
-adjust needle angle and advance 1-2 cm
Complications of the caudal approach include
high failure rate (false passages)
inadvertent IV injection or catheter placement
dural puncture
Adult considerations for performing the caudal approach include
test dose
incremental injections following negative aspiration
sacral anesthesia: 12-15 mL
lower extremity procedures: 20-30 mL
A combined spinal epidural offers
advantages of both while reducing disadvantages
Describe a two-level combined spinal-epidural.
spinal placed first
epidural catheter placed 1-2 levels above
Describe a one-level combined spinal epidural
placement of epidural needle
spinal needle passed through
small intrathecal dose injected
epidural catheter placed
Additional concerns for the combine spinal epidural include
intrathecal opioid effects on fetus
inability to ambulate after receiving narcotics
maternal hypotension & itching
Potential complications of combined spinal epidural are
failure to obtain either intrathecal or epidural block catheter migration increased spinal level metallic particles PDPH neurologic injury
For the obese patient it is more difficult to
palpate spinous processes as adipose tissue distorts anatomic landmarks
sitting position may provide more flexion- feet resting on a stool or “Indian” style
consider ultrasound
Neuraxial imaging facilitates
successful blocks in both normal and abnormal spinal anatomy because you can identify interspaces& determine depth to epidural space
Ultrasound has been shown to improve
patient safety and comfort
The ultrasound assisted neuraxial imaging is the most
common approach in adults
two scanning planes are required to determine level and midline
The real-time approach is
feasible in the pediatric population
Describe the two planes that must be scanned for neuraxial imaging.
parasagittal- paramedian, longitudinal view
axial- transverse, midline view
These factors regarding local anesthetic varies according to level and duration of block desired
type, volume and total dose
tailored to each patient & the surgeon’s needs
Little to no metabolism of local anesthetic in the
CSF
absorbed into plasma and metabolized based on its physiochemical properties
Adding vasoconstrictors will
slow absorption and prolong block
Considerations of the local anesthetics include:
density of block- concentration
spread of block- volume
think cephalad & caudal spread, positioning, elderly & pregnant
no more than 3-5 mL per injection & only after negative aspiration
The quickest onset of the esters is
chloroprocaine
The quickest onset of the amides is
lidocaine: DOA is 90-120 minutes
mepivacaine DOA is 120-240 minutes
Describe how the dosing differs between caudal, lumbar, & thoracic.
caudal: 2 mL/segment
lumbar: 1 mL/segment
thoracic: 0.7 mL/segment
Describe why epinephrine would be added.
alpha 1 agonist
concentration: 1:200,000 (15 mcg/mL)
prolong effect of short-acting local anesthetics
Describe why clonidine would be added.
it is NOT a vasoconstrictor
-selective alpha 2 agonist
when mixed with lidocaine or bupivacaine it has synergistic effects for labor analgesia
Describe the most commonly used epidural opiods.
fentanyl & morphine
a combination of preservative free opioids and local anesthetics provides better analgesia than if either drug is used alone
Describe the dose, onset, & duration of fentanyl.
dose: 50-100 mcg
onset: 3-5 minutes
duration: 1-2 hours
Describe the dose, onset, and duration of morphine
dose: 2-4 mg
onset is 10-15 minutes
duration: 8-10 hours
The adverse effects of morphine include:
itching & urinary retention
highly polarized, not very lipid soluble
The goal of epidurals is to block
A delta & C fibers
drug concentration typically exceeds requirements for all nerve types
A patient controlled epidural is a
low concentration infusion with additive
it augments effects of local anesthetic
patient has the ability to inject additional LA if needed
Describe the conservative treatment for PDPH.
first 12-24 hours
recumbent position, analgesics, fluid administration, caffeine, stool softeners and soft diet
An epidural blood patch can be used to
treat PDPH
injecting 15-20 mL of autologous blood
below initial puncture site (1-2 levels)
90% will respond to initial therapy
Signs and symptoms of PDPH include
bilateral frontal or retroorbital or occipital, extends into next, photophobia, nausea, positional
Risk factors for the PDPH include
needle size & type patient population (younger, female & pregnancy)
A postdural puncture headache results from
compromise in the dura
may be obvious or may follow uncomplicated procedure
List the complications associated with epidurals:
hypotension, intercostal muscle paralysis, apnea/phrenic nerve paralysis, paresthesia, SAH or epidural hematoma, meningitis/epidural abscess, chemical meningitis, cauda equina syndrome, transient neurologic symptoms, new nervous system lesion, exacerbation of preexisting neurologic disease, N/V, urinary retention, and post dural puncture HA
Documentation should include.
informed consent
oxygen/monitors applied; baseline VS
patient properly positioned
prepping and draping accomplished in sterile fashion
desired interspace identified
skin wheal of subcutaneous local anesthetic
introducer placed with spinal needle passed through introducer
positive clear CSF noted
dose of LA & any adjuncts
patient placed in desired surgical position
final dermatome level achieved
The autonomic blockade is usually
two dermatome levels higher than level of sensory block
The upper limit of motor block is generally
two levels below sensory block
Evaluation of your block should be assessed
every 2-3 minutes
Post block, it is important to assess
blood pressure & vital signs frequently
Physiologic changes closely resemble
block level
level is determined easiest by assessing sensory changes
-distribution of spread can be manipulated by adjusting level of OR table
B fiber block
is rapid -hypotension related to level T4= cardiac accelerator fibers drop in BP first sign N/V may follow
A delta & C pain fibers and temperature follow
B fibers
- unable to discriminate light touch or temperature
- temperature discrimination mirrors sensory loss
A alpha, A beta, & A gamma are last and include
touch & proprioception, surgical muscle relaxation, may feel pressure
