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
- leaks into intravertebral foramen and prarvertebral spaces
- medication spread is diffusion dependent
- onset longer
what does an epidural anesthetic block?
-temporary interruption of autonomic, sensory and motor nerve fiber transmission that is dependent on the drug concentration and volume of drug instilled into the space
advantages of epidural anesthesia
- reduces surgical stress
- reduces overall blood loss (debated in literature)
- decreases risk of DVT (MOA unknown, but maybe stops stress response and interrupts coagulation cascade)
- provides anesthesia and/or analgesia –> can re dose with catheter or convert from pain management to primary anesthetic
- it is versatile –> you can control the extent of the sensory and motor blockade; can be used with adjuncts
disadvantages of epidural anesthesia
- PDPH due to larger needle
- sympathetic blockade occurs 100% of the time (hypotension, bradycardia)
- block may last much longer than the procedure
- urinary retention
- regional takes “too much time”
- more difficult than spinal
why would you pick an epidural?
- discuss case with the surgeon, could be part of a multimodal pain management in ERAS
- management of labor pain
- procedures involving the abdomen or lower extremities
- certain comorbidities - pulmonary disease
absolute contraindications to epidural
- patient refusal
- increased ICP (can cause brainstem herniation)
- severe aortic or mitral valve stenosis
- coagulopathy or bleeding diathesis
- severe hypovolemia
- infection at the injection site
relative contraindications to epidural
- uncooperative patient (unable to sit still = dangerous)
- local anesthetic allergy (esters PABA)
- patient on anticoagulant or thrombolytic therapy (patients with comorbidities like atrial fib or DVT)
- preexisting neurologic defect
- chronic HA or backache
- severe spinal deformity
- valvular stenosis
patient assessment for epidural anesthesia
- preop does the patient understand the surgical technique
- explain spinal anesthetic and rational for preference
- address any patient concerns - fear of being awake or loss of control
- reassure patient
- NEVER force or coerce patient into any procedures
- age considerations
what is involved in informed consent
- 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 a general if already agreed to
pre-procedure monitoring
- PIV large bore
- have suction
- have airway supplies
- ECG, BP, Pulse ox, oxygen if needed
- supportive meds - induction agent, paralytic, atropine, vasoactive meds
- support person ready to stand with the patient the WHOLE time
positions used for epidural
- sitting
- lateral decubitus
- prone
neelde approaches for epidural
- midline
- paramedian
placement of epidural
- thoracic - spinous processes form a shield, need steep cephalad angle or paramedian approach
- lumbar - short, small spinous processes, midline OK
- caudal - in sacral hiatus; lateral or prone, needle almost parallel to spinal column
patient positioning
- have assistant stand in front of the patient; assistant does NOT leave patients side
- have patient hold pillow or blanket or lean over a table; drop their head down; roll their back
- angry cat or shrimp position
- flexion of the spine will create larger intraspinous spaces and make your procedure more successful
lateral approach patient psition
- maintain midline positioning
- limit spine rotation
what things do you need prior to the start of the procedure?
- patient IV
- monitoring devices
- oxygen attached and functioning
- resuscitation equipment available
- walk patient through procedure
prepping patient epidural procedure
- ensure proper positioning
- ensure comfortable for you too
- palpate landmarks with ungloved hand - iliac crests, spinous processes of lumbar vertebrae
- use most identifiable interspace (usually L2-3)
- examine one level above and one level below and if you can’t feel use ultrasound
- STERILE
- open tray and inspect integrity of components
- 3cc - local skin wheal
- 5cc - local injection
what must you wear for the procedure?
- hat
- mask
- sterile gloves
3 cc syringe
local skin wheal
5 cc syringe
local injection
steps of epidural procedure
- position patient
- find spot
- open tray using sterile technique
- prep patient with CHG or betadine - allow to dry
- set up tray and draw up medications (be consistent)
- cleanse site
- apply sterile drape with your site at the center of the circle
- straddle selected interspace with middle and index fingers of non-dominant hand
- raise a small intradermal skin wheal of LA with 25-27G needle (can advance as a guide to feel where you want to go)
- epidural needle placed with bevel cephalad
- advanced through - supraspinous, interspinous; advanced mm by mm; SLOW
- once through ligamentum flavum will feel loss of resistance
epidural needles
- marked in 1 cm increments
- large needles
standard epidural needle size
9 cm
touhy needle
- pronounced curve
- easier for novices
- directional placement of catheter
- want bevel up and curve facing caudad so the catheter threads up
crawford needle
- not curve
- easier to insert
- BUT higher rate of dural punctures
standard depth to ligamentum flavum at lumbar level
5 cm
varies with level and body habitus
bromage grip
- hand firm support to stabilize the needle
- attach and secure the syringe
- passing catheter through needles
- non-dominant hand stabilizes patient’s back
alternate grip
- attach and secure syringe
- needle placed with bevel cephalad
- hands to stabilize needle on both sides
loss of resistance method
- most common method
- glass or plastic syringe
- fill with 2-3 mL saline with air bubble
- attach to epidural needle
- resistance noted while needle is in the various ligaments until epidural space is entered
- pressure on back of needle; when feel loss of resistance, in the epidural space
hanging drop method
- hub of epidural needle filled with saline until small drop visible
- negative pressure created as needle passes into epidural spaces SUCKS drop in
- more pronounced at thoracic levels
dilation of epidural space
- once needle passes through the epidural space, immediate loss of resistance is noted
- contents of syringe injected into space
- when syringe is removed, common to see a small amount of clear fluid
- puncture of dura will result in LARGE amt of CSF
epidural catheters
- typically 2 gauges smaller than needle
- open-ended
- multiport - lower incidence of inadequate analgesia; higher incidence of accidental vein cannulation
- markings help to identify depth of catheter placement
dashed lines
1 cm
two dashed lines
10 cm
thick line
12 cm
catheter placement
- when thick black mark is flush with hub, catheter is flush with needle tip
- slight resistance noted when catheter is advanced
- if catheter has a stylet, retract prior to advancing
- inform patient of possible paresthesia (if one occurs STOP)
how far do you advance the epidural catheter?
3-5 cm past the needle hub
shallow placement
can get dislodged from epidural space
deep placement
- puncture of dura
- passage into epidural vein
- migration through intervertebral foramen
remove needle
- slowly withdraw needle over catheter
- once needle is removed, note the depth of the catheter at the skin
- if depth is less than 1 cm to the epidural space REPLACE
- never attempt to withdraw the catheter through the needle
test dose
- 1.5% lidocaine with epinephrine 1:200,000
- 15 mg/mL lidocaine and 5 mcg/mL epi
- inject 3 mL –> 45 mg lidocaine and 15 mcg epi
subarachnoid placement
spinal - hypotension brady
intravascular placement
greater than 20% increase in HR and BP
secure catheter
- looped and taped away from midline
- minimizes chance of dislodgement
- keep OFF spinous processes
- placed over shoulder
- secure label to end of catheter!!
paramedian approach
- useful when patient cannot flex spine (history of previous spine surgery, RA, or hip/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
- does NOT pass through supraspinous or intraspinous ligaments
contacting bone - troubleshooting
-withdraw needle and stylet to subQ fat, reposition the introducer and reinsert the needle
needle touching the superior crest of spinous processes below the intererspace
redirect cephalad
needle touching the inferior surface of spinous processes above the intererspace
redirect caudal
repeatedly encounter bone
remove and reassess landmarks
if patient experiences paresthesia during placement what do you do?
- STOP
- resolve ZINGER then proceed
- if persistent - withdraw and reposition (bc prob hit nerve root yikes)
what do you do if you get blood in your catheter
withdraw and replace!!!
caudal anesthesia
distal approach to the epidural space through the sacral hiatus
indications for caudal anesthesia
- hemorrhoidectomy
- chronic pain patients
- peds analgesia -inguinal herniorrhaphy, circumcision, perineal procedures
anatomy for caudal anesthesia
- technically difficult approach especially in adults, overall failure rate is about 5%
- sacral anatomy adults = variation in size, shape and orientation of hiatus
- sacral anatomy peds = more reliable
caudal anesthesia positioning
- prone on flexed table or with pillow under the pelvis
- legs spread and externally rotated
- laterally positioned for peds
caudal approach procedure
- puncture sacral hiatus
- adjust needle angle
- advance 1-2 cm
dosing for caudal
- 0.5-1 mL/kg of body weight
- varying LA concentrations
- 2.5 mg/kg body weight
caudal in adults
- test dose
- incremental injections following negative aspiration
- sacral anesthesia 12-15 mL
- lower extremity procedures 20-30 mL
caudal complications
- high failure rate (false passages like bone/subQ)
- inadvertent IV injection or catheter placement
- dural puncture
combined spinal epidural (CSE)
- initial subarachnoid injection followed by epidural catheter placement and subsequent administration of epidural medications
- allows for rapid relief of pain or induction of regional anesthesia by the rapid onset of the spinal drugs and subsequent administration of medications for prolonged anesthesia
- benefits of both spinal and epidural anesthesia
CSE two level
- spinal placed first
- epidural catheter placed 1-2 levels above
CSE one-level
- placement of epidural needle
- spinal needle passes through
- small intrathecal dose injected
- epidural catheter placed
CSE additional concerns
- intrathecal opioid effects on fetus
- inability to ambulate after receiving narcotics
- maternal hypotension and itching
CSE potential complications
- failure to obtain intrathecal or epidural
- catheter migration
- increased spinal level
- metallic particles
- PDPH
- neurologic injury
Obese patient and epidural anesthesia
- spinous processes more difficult to palpate, adipose tissue distorts landmarks
- sitting position may provide more flexion
- feet on stool or criss cross applesauce
- assistant at bedside throughout procedure
- consider ultrasound
neuraxial imaging
- US can identify epidural space more accurately than physical exam (71% vs 30%)
- two scanning planes offer acoustic windows for the assessment of spinal anatomy
- use low frequency curvalinear transducer
ultrasound assisted
- most common approach in adults
- two scanning planes to determine level and midline
- identify space, mark it, then stick it
real time
- feasible in peds population; caudal depth to space more shallow and angle flat
- limited studies on adults
what are the two scanning windows of neuraxial imaging
- parasagittal
- axial
parasagittal
- paramedian, longitudinal view
- off to sides and angle in toward midline
- find level - start at sacrum, next see ligament (L5), notch level with marker
axial
- transverse, midline view
- find spinous processes, know where to NOT go
- spinous process = unicorn or traffic cone
- space = bat sign
metabolism of LA in CSF
- little to none
- absorbed into plasma and metabolized based on physiochemical properties
- adding vasoconstrictors will slow absorption and prolong block
esters
- procaine
- chloroprocaine
- tetracaine
amides
- lidocaine
- mepivacaine
- ropivacaine
- bupivacaine
procaine
- pKa - 8.9
- % ionized - 97%
- % protein bound - 6%
- onset - slow
- DOA - 60-90 min
cholorprocaine
- onset - fast
- DOA - 30-60 min
tetracaine
- pKa - 8.5
- % ionized - 93%
- % protein bound - 94%
- onset - slow
- DOA - 180-600 min
lidocaine
- pKa - 7.9
- % ionized - 76%
- % protein bound - 64%
- onset - fast
- DOA - 90-120
mepivacaine
- onset - fast
- DOA - 120-240 min
ropivacaine
- onset - slow
- DOA - 180-600 min
bupivacaine
- pKa - 8.1
- % ionized - 83%
- % protein bound - 95%
- onset - slow
- DOA - 180-600 min
density of block
has to do with the concentration of the LA
spread of block
has to do with the volume
cephalad to caudal spread
positioning
elderly, preggo
how much LA do you inject into epidural space at a time
no more than 3-5 mL and ONLY after negative aspiration
caudal dosing
2 mL/segment
lumbar dosing
1 mL/segment
thoracic dosing
0.7 mL/segment
epinephrine additive
- alpha 1 agonist
- concentration added 1:200,000 or 5 mcg/mL
- will prolong the effect of short-acting LAs by keeping it in the space
clonidine additive
- not a vasoconstrictor
- selective alpha2 agonist
- when mixed with lido or bupivacaine has synergistic effects for labor analgesia
- potentially some direct action on the nerves
epidural opioid additive
combination of preservative free opioids and LAs provides better analgesia then if either drug is used alone
-most commonly used = fentanyl and morphine (ITCHY)
fentanyl additive
- HIGH lipid solubility
- PK and PD similar to systemic admin
- provides profound analgesia
- dose = 50-100 mcg
- onset = 3-5 min
- DOA = 1-2 hours
morphine additive
- HIGHLY polarized, not very lipid soluble
- PK/PD similar to systemic admin
- provides profound analgesia
- dose 2-4 mg
- onset 10-15 min
- DOA 8-10 hrs
- AEs = itching and urinary retention
patient controlled epidural
- low concentration of infusion with additive
- augment effect of LA
- patient has ability to inject additional LA if needed
GOAL
block A delta and C fibers
drug concentration typically exceeds requirement for all nerve types
a alpha
proprioception, motor
last block onset
a beta
touch, pressure
intermediate block onset
a gamma
muscle tone
intermediate block onset
a delta
pain, cold temperature touch
- 1-5 micrometers in diameter
- heavy myelination
- intermediate block onset
b fibers
preganglionic autonomic vasomotor
- <3 micrometers in diameter
- light myelination
- early block onset
C sympathetic fibers
postganglionic vasomotor
early block onset
C dorsal root fibers
- pain, warm and cold temperature, touch
- 0.4-1.2 micrometers in diameter
- no myelination
- early block onset
B fiber block
- rapid
- hypotension r/t level
- T 4 = cardiac accelerator fibers
- drop in BP first sign
- N/V may follow
A delta and C pain fibers
- these fibers along with temperature follow b fibers
- unable to discriminate light touch or temperature
- temperature discrimination mirrors sensory loss
a alpha, a beta, a gamma
LAST
- touch a proprioception
- surgical muscle relaxation
- may feel pressure
nerve block onset fibers from earliest to last
- B
- C and A delta
- A gamma
- A beta
- A alpha
evaluation of onset
- asses every 2-3 min
- frequent assessments - BP/VS
- physiologic changes closely resemble block level
- level determined easiest by assessing sensory changes
- distribution of spread can be manipulated by adjusting level of OR table
autonomic blockade
usually 2 levels higher than level of sensory block
motor block
upper limit generally two levels below sensory block
complications of epidural anesthesia
- hypotension
- intercostal muscle paralysis
- apnea/phrenic nerve paralysis
- paresthesias
- subarachnoid 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
- PDPH
Post dural puncture headache (PDPH)
- results from compromise in dura
- risk factors include - needle size and type, patient population (young, female, preggo)
S/S PDPH
- bilateral frontal or retroorbital or occipital
- extends into neck
- photophobia
- nausea
- positional
PDPH treatment
- conservative for first 12-24 hours (recumbent position, analgesics, fluids, caffeine, stool softeners and soft diet)
- epidural blood patch
- if that doesn’t work consider other sources
epidural blood patch
- injecting 15-20 mL of autologous blood
- below initial puncture site (1-2 levels)
- 90% will respond to initial therapy
