Epidural Anesthesia Flashcards
Does epidural or spinal anesthesia offer better control of the extent of motor and sensory blockade?
epidural
Distinct difference between epidural and spinal anesthesia?
epidural allows for continuous administration of anesthesia secondary to placement of a catheter
How do LA or analgesics injected in to the epidural space spread horizontally?
spread to the regions of the dural cuff, where it is able to diffuse in to the CSF and leak in to the intravertebral foramen and paravertebral spaces to achieve analgesia/anesthesia
How does epidural medication spread longitudinally?
cephalaud
Why do you have to use larger volumes of medication with epidurals than with spinals, and how much is the usual volume?
because the medication is diffusion dependent; 20 mL, spinals 1-2 mL
For an epidural where is the LA injected?
epidural space
How is the onset of an epidural in comparison to a spinal?
slower and not as dense
What do the arachnoid villi and granulations on the dural cuffs of the sleeves do?
reduce the thickness of the dura mater, which permits rapid diffusion of anesthetics from the epidural space thru the dura and into the CSF
What property of the anesthetics may account for differences in diffusion rates across the dura?
lipid solubility
Why/how does epidural anesthesia take longer to act?
medication be delivered to the subarachnoid space by the process of diffusion and spread
This type of anesthesia is useful for procedures of unpredictable duration, prolonged post op analgesia, and chronic pain control?
epidural
Only anesthesia available to relieve labor pain and minimally effect baby/maternal physiology?
epidural
What type of block is an epidural (ie sensory or motor)?
sensory w out motor block
What can you dilute the LA with in epidural?
opioid
5 indications for epidural?
longer lower dermatome surgery, postop analgesia, labor analgesia, pain treatment, combo techniques
Where does needle go in spinal versus epidural?
spinal: practitioner seeks CSF by piercing the dura; epidural: tip of epidural needle seeks fat filled space deep to ligamentum flavum and shallow to the dura
Typically, an epidural catheter is what size in comparison to the needle?
2 gauges smaller than the needle
What are the uniport and multiport epidural catheters?
uniport: single holed, open ended; multiport: lateral holed, closed tip
Studies show a significantly lower incidence of inadequate analgesia and higher incidence of inadvertent IV cannulation with what epidural catheters?
multiport
Manufacturers recommend that epidural catheter should be threaded how many cm into the epidural space?
3-5
Not threading catheter far enough in to the epidural space can cause? And threading it too far can cause?
inadequate analgesia; IV cannulation
The standard epidural needle is what size and how long?
16-18 g and 3 inches long
The blunted bevel and gentle curve of the epidural needle allow for what?
allow passage thru the skin and ligamentum flavum and abut against the dura, rather than penetrate thru the dura
Two most common epidural needles?
Tuohy and Hustead
Difference between Tuohy and Hustead needle?
Tuohy is easiest for novel practitioners and its blunt, curved tip is less likely to penetrate the subarachnoid space. Hustead has a less pronounced 15 degree curvature which can more easily pass thru the skin and ligamentum flavum
This is a third epidural needle and it is preferred when catheter placement in to the epidural space is difficult, the angle is steep?
Crawford
This type of epidural catheter has been implicated in a higher ratio of accidental dura punctures?
Crawford
Any procedure below the diaphragm would get what type of epidural?
lumbar
2 approaches to lumbar epidural?
midline or paramedian
This epidural is most commonly used for postop analgesia?
thoracic epidural
This approach with a thoracic epidural is usually easier?
paramedian
Thoracic epidural can be used as a single shot for?
chronic pain management
Big risk with thoracic epidural?
spinal cord injury
How is the ligamentum flavum in the cervical region?
very thin
Position for cervical epidural?
sitting position, neck flexed
What type of approach do you do for cervical epidural?
midline
What type of approach do you do for thoracic epidural?
midline or paramedian
Single shot cervical epidural used for?
chronic pain management
Standard of care for cervical epidural is evolving to be?
placement under fluro
This type of epidural is placed in the sacral epidural space found at the sacral hiatus?
caudal
3 positions to do caudal epidural in?
lateral, prone, jackknife
2 types of surgeries which would use caudal epidural?
perineal and sacral
3 techniques to find epidural space?
fluoro, loss of resistance, hanging drop
How do you do the hanging drop technique?
hub of needle is filled w fluid so drop hangs from it, negative pressure in epidural space sucks fluid into the needle
How do you do the loss of resistance technique?
attach fluid or air filled syringe to needle after entering interspinous ligament, advance needle mm by mm while tapping on plunger, sudden loss of resistance is felt when entering space
Most common method used to enter the epidural space?
loss of resistance
Stylet of epidural needle is removed once entering?
when needle is placed thru intraspinous ligament, or ligamentum flavum
What type of solution do you put in syringe for loss of resistance technique?
NS or air
As the needle passes thru the ligamentum flavum what happens to resistance?
it increases
Profuse return of CSF results when penetration of epidural needle is where?
dura
3 types of tests which can confirm CSF vs NS or LA?
CSF is warm, NS or LA is room temp, glucose test paper detects glucose in CSF, LA mixed with similar amt of thiopental immediately forms a precipitate
What frequency is the US probe used for spinals and epidurals?
low frequency (2-5 Hz)
Ultrasound transverse and midline approach allows for what?
midline: identify midline and assess distance; transverse approach assessment of interspace
2 positions for US epidural placement?
lateral with knees flexed and hips or sitting position with back curved out to present spines
Where do you start with placement of US for epidural?
sacral region, 3 cm lateral to left of midline and slightly angled toward center of spine
First anatomy to identify using US for epidural?
identify sacrum, which is the white hyperechoic bone
When using US, after you identify the sacrum, what do you do?
move US cephalaud until hypchoic sawlike images (articular processes) are seen
Once the articular processes are seen, what do you do when using US?
mark exact level of spinous processes
When using US, what is between the sawlike images?
vertebral interspaces
When using the US, after you identify the exact level of spinous processes and and each interspace, what do you do?
Place the probe horizontal along the midline of the spine at the marked levels of the interspace and spinous processes
How do you identify the hyperchoic spinous process?
use long triangular hypochoic shadow
Once a clear image is captured of the interspace, ligamentum flavum, an dorsal dura mater on the US what do you do?
freeze screen, mark the midline along the right lateral surface of the probe
How do you determine the insertion point of an epidural?
it is determined by the intersection of the extensions of the 2 markings on the skin in the horizontal and vertical planes. one mark identifies the midline and the other identifies the interspace
Using the US how do you mark the distance to the ligamentum flavum?
freeze the screen on the transverse view; place one prong of calibers at skin and other at inner side of ligamentum flavum
As the catheter is passed in to the epidural space, what might the pt feel?
funny bone sensation down leg
If that funny bone paresthesia is present prior to or after needle removal what needs to be done?
withdraw catheter and replace it bc it may be lodged in to nerve root
What can injection of medicine in to pt complaining of paresthesia do?
nerve root damage, nerve root death and cause long term morbidities
If the catheter is being replaced secondary to a persistent paresthesia, it is best to?
move to a new interspace to avoid oversensitized nerve roots
You don’t want to puncture what space?
subarachnoid
Why should you never withdraw the catheter thru the needle?
that can shear the catheter and embed foreign material in the patient’s back
Distance from skin to epidural space in adults is?
4-6 cm
Typical size of epidural catheter?
19 or 20 gauge
Problem with shorter distance catheter placement?
disloged easily
Problem with longer distance catheter placement?
can exit epidural space via foramen
After catheter placement and needle removal, does gravity alone produce CSF?
no so may need to attach a syringe and gently aspirate
Does a negative aspiration test guarantee that the catheter tip is in the epidural space? why?
no bc tissue at the catheter tip may create a ball-valve effect
Only if ____________ does aspiration test confirm that the catheter tip is placed either into an epidural vein or the subarachnoid space?
fluids return
The return of CSF or blood for aspiration test indicates that the catheter should be ?
removed and replaced at a different interspace
To avoid this ball-valve effect or to dislodge any skin or tissue that may have lodged at the catheter tip, some practitioners advocate?
injection of 1 to 2 mL of normal saline solution through the catheter to confirm catheter patency before injection of medications
After needle removal, the catheter should be taped where?
away from the midline of the back to avoid spinous processes and minimize the risks of catheter displacement from the epidural space or pressure injuries over bony prominences
Prior to injection of a large amount of medication into an epidural space, what is done?
a test dose of a small amount of medication is administered to determine whether the catheter or needle has inadvertently entered the subarachnoid space or possibly threaded into an epidural vein
4 s/s of intravenous lido?
tinnitus, a metallic taste, circumoral numbness, or a rushing sound in the ears
Duration of test dose effects?
____ mcg of undiluted fentanyl can be injected as a test dose to avoid potential complications caused by even low doses of epinephrine? If the needle or catheter is intravascular, the patient will experience?
100; immediate dizziness and sleepiness from the opioid
If the needle or catheter tip is in the subarachnoid space, this dose will result in; If the same test dose is injected into a blood vessel, the 15 mcg of epinephrine will result in?
spinal anesthesia within 3 minutes; a 20% rise in heart rate and systolic blood pressure within 30 seconds
What is meant by a wet tap?
dural puncture
6 technical probs when inserting epidural catheter?
missing midline (epidural space); wet tap (dural puncture); shearing of catheter; pt paresthesia; inability to advance catheter; aspiration of blood or CSF
What types of solutions are better for surgical epidurals?
more concentrated
More concentrated epidural solutions have what type of onset and what type of block and what type of duration?
faster onset; motor and sensory/more complete block; longer duration
Example of less concentrated solution for pain management?
marcaine 0.0625%
An addition of opioid improves what for an epidural block?
quality, not duration
Test dose for epidural should be?
3 mL of LA with epi
Intrathecal epidural admin produces what?
spinal anesthesia
Intravascular epidural admin produces what?
tachycardia
What should you do before each epidural injection?
aspirate
An epidural block relative to SAB requires what amt of LA?
larger volume and concentration
Type of onset for chloroprocaine, lido, bupivacaine, and ropivacaine?
fast; intermediate; slow; slow
Chloroprocaine is more likely to be what kind of toxic?
neuro
Bupivacaine is more likely to be toxic to what?
cardio
2 seg regression for chloro, lido, bupiva, ropiva?
30-90 min; 60-120 lido; 120-140 bupiva; 120-140 ropiva
Lumbar, cervical, and thoracic dosing?
lumbar: 1-2 mL per segment to be blocked; cervical and thoracic: 0.7-1 mL per segment to be blocked
What’s the process in aspirating and injecting LA for epidural?
aspirate, then inject 3-5 mL q3 min and titrate to desired level
What type of dose would you use for an epidural redose?
1/3-1/2 of initial dose in an appropriate time frame based upon pharmacokinetics
7 factors affecting spread of LA?
dose (vol x concen), concentration of LA, volume of LA, site of injection, size of epidural space increases down the cord, age, body stature (height, weight, pregnancy)
Drug concentration affects what?
density of block
Drug volume affects what?
spread of block
What happens in cervical area for LA drug distribution?
less drug spreads across more area in cervical than lumbar regions
Amt of LA needed does what with age?
decrease
This is the process by which an AP is conducted from the periphery to the CNS?
transmission
This system carries the pain signals from the trunk and lower extremities?
spinothalmic/anterolateral
The primary afferent neurons are?
a delta and c fibers
Where are the primary afferent neurons located?
in dorsal root ganglia of spinal cord
Upon entering the dorsal cord, these fibers/ a delta and c fibers segregate and ascend or descend several spinal segments where?
in the tract of Lissauer
After leaving the tract of Lissauer, the axons of the primary afferents (a delta and c fibers) enter the gray matter of the dorsal horn where they?
synapse with second-order neurons
Where do afferent a delta and c fibers terminate?
primarily in Rexed’s laminae I, II, and V
What types of second order neurons are there?
nociceptive neurons, wide dynamic range neurons
These neurons receive input solely from primary afferent Aδ and C fibers?
nociceptive
These neurons receive input from both nociceptive (Aδ and C fibers) and non-nociceptive (A-β) primary afferents?
wide dynamic range neurons
Wide-dynamic-range neurons are therefore activated by?
variety of stimulants: inoccuous and noxious
Opioids can be added as adjunct to epidural because there are opioid receptors where?
dorsal horn of spinal cord
The analgesic response of opioids in epidural is the resultofactivity atspinalopiate receptors, especially _____ receptors in the ___________?
kappa; substantia gelatinosa, lamina IIofthedorsalhorn
Opioids can be given with local anesthetics or other adjuncts when?
initiation of spinal or post op for pain control
Side effects with opioid spinal admin are the same as systemic effects except?
pruritis and urinary retention occur w much greater frequency
Why do you have to be careful with morphine and hydromorphone?
they’re less lipid soluble and produce delayed vent depression
In comparison to oral or parenteral admin of opioids how does the spinal dose change?
spinal dose is smaller
Combined epidural and light GA: epidural provides what 2 things and does what to adjunctive anesthesia requirements?
analgesia and muscle relaxation and decreases the requirements for adjunctive anesthetics
When would combined epidural and light GA be good?
RRP, thoracic, pts with significant pulmonary pathology
Why would you use combined spinal and epidural (CSE)?
fast onset of SAB and continous epidural
What are two classes of surgeries which CSE is good for?
OB, some ortho
How would you do a CSE?
insert tuohy needle into epidural space and insert long 27 g spinal needle thru tuohy needle, inject intrathecal narc, remove SAB needle and insert epidural catheter
How could you do a CSE for outpt surgery?
inject lido in to intrathecal and epidural space
2 signs of sympathetic blockade?
hypotension, bradycardia
What are the cardiac accelerator fibers?
T1-T4
To assess motor block, ask pt to do what?
lift leg, wiggle toes
What can you do if inadequate block?
convert to GA, reattempt block
Objective evidence of blockade w/in how many minutes?
5 minutes
Use of plain local anesthetic solutions in the epidural space to create a high level of blockade will decrease what 5 things?
the mean arterial pressure, cardiac output, stroke volume, heart rate, and peripheral vascular resistance
HD changes from spinal/epidural are attributed to sympathetic blockade and therefore?
arterial venous dilation
What concen of epi would you add to LA?
1:200,000 or 1:400,000
What does the addition of epi to LA do?
diminishes and slows systemic uptake, resulting in lower plasma levels of the local anesthetic and prolongation of its duration of action
Epinephrine is thought to be absorbed systemically in low levels, thereby causing __-adrenergic vasodilation
B2
5 meds to treat hemodynamic alterations from epidural analgesia?
ephedrine, phenyl, dopam, glyco, atropine
One complication that is more prevalent with epidural anesthesia than spinal anesthesia is _________?
backache
The incidence of back pain after epidural anesthesia is between ___ and ___, especially in the obstetric patient
30-45%
Signs and symptoms of neurologic compromise (4)?
spine ache, root pain, weakness, and bowel or bladder dysfunction
8 complications of epidural?
HD changes, LA toxicity, injection of LA in to CNS, dural puncture and subsequent HA, trauma on removal of catheter, backache, epidural hematoma, epidural abscess
For placement of epidural catheters, the PDPH rate is ?
1-2%
Epidural needles are ____ in diameter compared with spinal needles?
large
With such a rent in the dura, the incidence of PDPH can be as high as __% in young patients?
75
________ catheters are also more likely to place a patient at risk for neuraxial anesthesia complications
Epidural
