Neuraxial Anesthesia and Local Anesthetic Flashcards
Where does the spinal cord end in adults?
L1-L2
Where does the dural sac end in adults?
S2
Where does the spinal cord end in children?
L2-L3
Where does the dural sac end in children?
S3
Name the 7 layers of the spine from skin to CSF
- Skin
- Supraspinous ligament
- Interspinous ligament
- Ligamentum flavum
- Epidural space
- Dura mater
- Subarachnoid space (contains CSF)
the epidural space extends superiorly to the _____ and inferiorly to the _____
foramen magnum
sacral hiatus
\_\_\_\_ cervical vertebrae \_\_\_\_ thoracic vertebrae \_\_\_\_ lumbar vertebrae \_\_\_\_sacral vertebrae \_\_\_\_ coccyx vertebrae \_\_\_ total vertebrae
7 12 5 5 4 33
\_\_pair of cervical nerve roots \_\_ pair of thoracic nerve roots \_\_ pair of lumbar nerve roots \_\_ pair of sacral nerve roots \_\_ pair of coccygeal nerve roots \_\_total spinal nerve roots
8 12 5 5 1 31
As nerve roots exit the spinal canal they are covered by dural sheath.
- . Roots close to the spinal cord tend to float in the dural sac, and are thus usually (pushed away/ pierced) by an advancing needle
- Nerve blocks close to the intervertebral foramen carry a risk of ____
- pushed away
2. subdural injection
For adults, what interspace is the most common starting insertion site for a spinal or a lumbar epidural?
L3-L4
If an L3-L4 spinal/epidural fails, what interspace should be the next option?
L4-L5
If an L3-L4 AND L4-L5 spinal/ epidural fails, what interspace should be the next option?
L2-L3
an imaginary line that is drawn between the superior aspects of the iliac crests
Tuffier’s line
What interspace does Tuffier’s line estimate?
L4-L5 interspace
-In order to find L3-4, the anesthetist simply palpates the superior aspects of the iliac crests, and moves up one interspace above Tuffier’s line
What does the T10 dermatome represent?
umbilicus
What 3 surgeries is a T10 level of analgesia needed for?
- Spontaneous vaginal delivery
- T10-L1 is the goal dermatome level of a block for laboring patients planning on regular vaginal delivery - Inguinal surgery
- Testicular surgery
What does the T4 dermatome represent?
Nipple
What dermatome level is needed for a C-section
T4
What dermatome level is the most dependent area of the spine when the patient is supine?
T4
Why is having the T4 dermatome as the most dependent area of the spine conveneint?
- if we lay patients supine after a spinal block it will USUALLY go to the perfect height necessary for analgesia for a C-section (T4)
- It helps prevent the spread of local anesthetic above T4, which helps prevent high spinal or total spinal anesthesia
What dermatomes represent vasomotor tone?
T5-L1
When ___ nerves are blocked with a spinal or epidural, it causes a sympathectomy
T5-L1
Because spinal blocks will typically settle at T4 in supine patients, virtually all patients laid in the supine position after a spinal block will have some degree of sympathectomy
What is the earliest sign of an intense sympathectomy?
nausea and vomiting
-profound hypotension causes nausea
how is nausea in a sympathectomy best treated?
by raising the patient’s blood pressure
sympathectomies are more severe with (spinal/ epidural)
spinal
-Epidural boluses can still produce a sympathectomy (if they happen to rise above T1
What dermatomes represent the cardiac accelerator fibers?
T1-T4
What happens if the neuraxial block rises above the T4 dermatome?
the patient can have significant bradycardia
What dermatome represents the phrenic nerve?
C3-C5
What happens if the neuraxial block gets to C3-C5 dermatome level?
the phrenic nerve will be knocked out and the patient will go apneic
What dermatomes represent the hands/fingers?
C6-C8
How do we know if the neuraxial block is getting to C6-C8 dermatome?
patient will experience tingling, numbness, and/or weakness in their fingers
What are we concerned about if the neuraxial block gets to C6-C8?
we are in danger of knocking out the patient’s respiratory drive, because if we get any higher we’d be knocking out C3-C5 (the phrenic nerve)
If a patient starts to experience tingling/ numbness in their fingers after a neuraxial block, what should the anesthetist do?
Place the patient in reverse trendelenburg to cause the medicine to sink in the spinal cord
T4-T5 dermatome landmark
carina
T6 dermatome landmark
xyphoid process
T6-T11 dermatome landmark
liver
T7 dermatome landmark
inferior border of the scapula
T8-L1 dermatome landmark
kidney
T10 dermatome landmark
orchiectomy
S2-S4 dermatome landmark
bladder
What type of blockade has the potential to produce hypotension and bradycardia?
sympathetic blockade
What type of blockade produces an absence of pain?
Sensory blockade
What type of blockade will block the patient’s ability to move those limbs?
motor blockade
Sympathetic blockade is typically___levels higher than sensory blockade, and sensory blockade is typically ___ levels higher than motor blockade
2
2
If a patient has a sensory block at T4, where will the motor and sympathetic block be?
motor: T6
sympathetic: T2
nerves are more easily blocked if they are (smaller/bigger) and (myelinated/ unmyelinated)
smaller
myelinated
What size Tuohy needle is used for an epidural?
17 ga
4 advantages to an epidural compared to a spinal
- we can give analgesia as long as necessary
- we have more control over the analgesic level
- can alter the dose - patients experience a less profound sympathectomy
- the block is less dense than the spinal - better preservation of motor block
- The better preservation of motor function with epidurals allows more effective “pushing” during a spontaneous vaginal delivery
4 disadvantages to an epidural compared to a spinal
- epidural block is not as dense as a spinal block
- patients undergoing C-sections under epidural anesthesia are not as likely to be as comfortable as if they had had a spinal block - There is a very high probability for post dural puncture headache (PDPH) if the dura is accidentally punctured
- The larger the needle used for the block, the larger the hole in the dura, which leads to a larger CSF leak, and a higher chance for post dural puncture headache - the onset of action for local anesthetics is longer for epidurals than it is for spinals
- Spinal onset is immediate, whereas epidurals are several minutes - There is more potential for local anesthetic toxicity with epidurals than there is with spinals
- the overall local anesthetic dose with epidurals is higher than it is with spinals
What is a “walking epidural” and what 2 things is the epidural usually dosed with?
preserves motor function and allows the patient to walk
can be dosed with narcotics only OR Lower doses/infusion rates of local anesthetic
is the dura punctured in an epidural? where is the local anesthetic injected in an epidural?
no
injected in the epidural space before the dura via a catheter infusion
is the dura punctured with a spinal? where is the local anesthetic injected in a spinal?
yes
in the subarachnoid/ intrathecal space via a single shot
What are the 4 different sizes used for a spinal needle?
27 ga, 25 ga, 22ga, 20 ga
smaller than an epidural needle
Why are smaller needles used in a spinal?
because the dura will be punctured and a smaller hole in the dura reduces the chance of a post dural puncture headache
pencil point spinal needle with the smallest opening
Whitacre
-opening (CSF aspiration will be the hardest/slowest)
pencil point spinal needle with a bigger opening
Sprotte
-Has a longer opening (easier to aspirate CSF, but a higher chance of injecting epidurally)
spinal needle with a cutting tip
quincke
-Cuts through ligaments better, but makes a larger hole in the dura
What size is the spinal introducer needle?
18 ga
What is the purpose of the introducer needle in a spinal?
allows much less bending of the spinal needle as the spinal needle passes through the spinal ligaments
When do you usually use an introducer needle in a spinal?
When the spinal needle is smaller than 22 ga
What is the advantage of a 22 ga spinal needle?
an introducer needle is not needed
What is the disadvantage of a 22 ga spinal needle?
there is a higher risk of spinal headache due to the larger hole in the dura
What are the 2 common uses for a 22 ga spinal needle?
- Elderly patients
- carry a lower risk of post dural puncture headache
- larger needles can pass through calcified ligaments more easily - obese patients
- A larger needle is less likely to bend/break when passing through the excess tissue
What is the most common size spinal needle in adults?
25 ga
what is the advantage of using a 25 ga spinal needle?
it’s way less likely for the patient to get a spinal headache (due to a smaller hole in the dura)
What is the disadvantage of using a 25 ga spinal needle?
it’s more likely to bend when passing through the spinal ligaments, and especially if the spinal ligaments are calcified (like in elderly patients). Because of this, a 25ga spinal needle is commonly used with an 18ga introducer
What is the advantage to the 27 ga spinal needle?
it creates the smallest hole in dura= least chance for PDPH
what is the disadvantage of the 27 ga spinal needle?
it has the highest chance of bending through the spinal ligaments
When is the 27 ga spinal needle typically used?
if we are performing a combined spinal epidural (CSE) block, where a Tuohy needle is used as the introducer needle
-Tuohy needle completely bypasses the spinal ligaments (which means that the 27ga spinal needle will only need to pass through the Dura and won’t really have any risk of bending/breaking)
______is currently a rare technique that provides repeated doses of local anesthetic into the intrathecal space through a catheter
continuous spinal anesthesia
what is the difference between an epidural and continuous spinal anesthesia?
continuous spinal anesthesia is dosed through a catheter in the intrathecal space and the dose is significantly lower and usually dosed in boluses instead of an infusion
Why are small micro catheters NOT used for continuous spinal anesthesia?
problem with these smaller microcatheters (24-32ga) is that their use is associated with neurotoxicity and cauda equina syndrome, possibly due to pooling of local anesthetics in a localized certain area
When is the only time continuous spinal anesthesia is acceptable?
when its through a large epidural catheter
-the only real practical use for continuous spinal anesthesia is if an anesthetist unintentionally punctures the dura with a Tuohy needle during epidural placement, and then decides to just thread the catheter into the intrathecal space and provide analgesia with a much lower dose of local anesthetic rather than attempt another epidural
How far should the catheter be threaded into the intrathecal space for continuous spinal anesthesia?
2-3 cm
How is analgesia maintained in continuous spinal anesthesia? (bolus/infusion)
bolus
what should the continuous spinal catheter be flushed with after each injection of local anesthetic?
previous aspirated CSF fluid after each
How long should you wait between dosing a continuous spinal?
45-90 minutes
if you bolus a continuous spinal too frequently, what can happen?
sacral pooling of the anesthetic and caudal equine syndrome
The dose of local anesthetic via continuous spinal infusion is approximately ____ the epidural infusion rate and titrated to effect
one-tenth
side effects associated with opioids (pruritus) are more common when the agent is delivered into the ______
subarachnoid space
When the two techniques (placement at a second lumbar epidural space versus continuous spinal infusion with an epidural catheter) are compared, a lower incidence of postdural puncture headache is noted with a ____
continuous spinal infusion
_____refers to how dense (heavy) the drug is compared to CSF, and the density of drug determines whether the drug will sink or rise when injected into the CSF
baricity
(hyperbaric/ hypobaric/ isobaric) spinal drug means that the spinal drug is denser (heavier) than CSF, so the drug will sink (follow gravity)
hyperbaric
Drugs are made hyperbaric by adding an equal VOLUME of ______ to the local anesthetic
10% dextrose/glucose
hyperbaric solutions have a:
- (shorter/longer) time to peak concentration
- (Shorter/longer) duration of action than plain local anesthetics
- shorter
2. shorter
A ______is performed by allowing the patient to remain sitting for several minutes after injecting hyperbaric spinal medication
saddle block
-This causes the medication to sink to the pelvis, anesthetizing the sacral nerves, buttocks, perineal area, and inner thighs
When anesthetizing this area with an epidural bolus, the term______ is used interchangeably with the term “saddle block”
perineal dose
what 2 common things are “saddle blocks” used for?
- genitourinary procedures
2. relieves 2nd stage labor pain
A (hyperbaric/ hypobaric/ isobaric) spinal drug means that the spinal drug is lighter than CSF, so the drug will rise (travel opposite to gravity)
hypobaric
Drugs are made hypobaric by adding ______
sterile water
- 3mL sterile water per 1mL local anesthetic
- 1mL sterile water per 1mg local anesthetic
what is the most common use for a hypobaric spinal?
hip surgery
-The spinal is performed with the patient in lateral position with the operative hip up
An (hyperbaric/ hypobaric/ isobaric) spinal drug means that the spinal drug has the same specific gravity as CSF, so it remains at the level of injection
isobaric
Drugs are made isobaric by adding an equal VOLUME of ____ or ______ to the local anesthetic
CSF or normal saline
Baricity applies to (spinals/epidurals/ both) and the baricity settles after ______ depending on the onset of the local anesthetic
spinals
10-15 minutes
after 15 minutes, the drug shouldn’t rise or sink as much based on the patient’s position
How is the combined spinal epidural (CSE) performed?
- Advances a CSE Tuohy needle into the epidural space
- Threads a spinal needle THROUGH a small hole in the CSE Tuohy needle and performs a spinal block, and removes the spinal needle while keeping the epidural needle in place
- Threads an epidural catheter after the patient has been dosed with spinal drugs
in a CSE, the spinal is used for _____ anesthesia and the epidural is used for _____ anesthesia
operative
postoperative
What is the most common CSE needle set and what does it contain?
Espocan
27 ga spinal needle and a Touhy needle with hole in the end for passage of the spinal needle
3 advantages of a CSE
- provides a denser block for a procedure than an epidural alone would
- allows a spinal to be performed with a 27 ga which leads to the smallest chance of a PDPH
- It allows postop analgesia with an epidural in case the anesthetist doesn’t want to use Duramorph in the spinal
What is the main disadvantage of a CSE?
an anesthetist can’t perform a test dose through the epidural catheter to make sure that it’s in the right place (to make sure that it’s not intrathecal or intravascular), because the patient is already numb from the spinal block by the time the epidural catheter gets threaded
How is a Dural Puncture Epidural technique performed?
- an epidural needle is placed
- spinal needle is inserted through the Touhy needle and punctures the dura
- the spinal needle is removed WITHOUT injecting any medication into the intrathecal space (leaves a small hole in the dura)
- epidural catheter is placed and hooked up to an infusion pump
- the local anesthetic primarily goes into the epidural space but a small portion LEAKS into the intrathecal space through the small hole
3 advantages to a Dural Puncture Epidural technique
- faster sacral onset
- greater sacral spread of local anesthetic
- lower incidence of unilateral block
What is the primary disadvantage of a dural puncture epidural technique?
small chance of PDPH
This is the site of needle insertion, and it is covered by the sacrococcygeal ligament
sacral hiatus
These are bony prominences just to the sides of the sacral hiatus
The anesthetist palpates these landmarks to find the sacral hiatus
sacral cornu
how is a caudal block performed?
inserting a needle through the sacrococcygeal ligament and into the sacral hiatus, the medication is injected into the epidural space
What are 2 ways in which a caudal block differs from an epidural block?
- Performed at the sacral level
2. Dosed with a single shot of drug (instead of a catheter infusion)
in a caudal block, how is the needle inserted into the sacral hiatus
at a 45 degree angle cephalad until a pop is felt
What is a common anesthetic dose for a caudal block?
1-1.25mL/kg of 0.125% marcaine with epi
Why are caudal blocks performed mostly in children and epidurals performed mostly in adults?
when epidurals are performed in the lumbar or thoracic region, it is vital that the patient be awake (so that they can alert the anesthetist of any parasthesias) to reduce the chance of nerve injury- closer to the spinal cord
kids will not tolerate holding still so caudal blocks can be safely performed in asleep patients, because the patient doesn’t need to be awake to alert the anesthetist of any parasthesias- farther away from the spinal cord
3 advantages of caudal anesthesia
- They can be performed in asleep patients, which makes it a popular epidural block for children
- They provide more reliable perineal anesthesia than lumbar epidurals do
- There is a less likely chance of dural puncture and nerve damage when compared with a lumbar epidural
5 disadvantages of caudal anesthesia
- The dura can still be theoretically punctured if the needle is advanced too far
- The rectum can be punctured if the needle is advanced at too steep of an angle
- The block is technically more difficult in adults
- It requires approximately twice as much local anesthetic drug as a lumbar epidural
- “However, if the catheter is threaded to the S1 level, the dosage can be decreased by one-third” - There is a relatively higher risk of urinary retention with this block
why aren’t caudal blocks performed in adults?
- anatomy can be difficult to find
2. larger doses are needed leading to greater chance of drug toxicity
How does epi affect the strength and spread of a neuraxial block?
prolongs the block but does not increase the spread
Does volume or dose play a bigger role in the spread or strength of local anesthetics?
volume and dose both affect the spread of local anesthetic but dose has a stronger effect than volume
higher doses of local anesthetic spread (more/ less) than lower doses
more
what do the addition of narcotics do to local anesthetics?
increases the density or “strength” of the block
shorter patients should recieve a (lower/higher) dose of local anesthetic
lower
-The shorter you are, the more likely the block will travel “too high”
The more obese the patient:
- the (higher/ lower) the anesthetic will spread
- the (higher/lower) the local anesthetic dose requirement
- higher
- these patients have increased intraabdominal pressure and compression of the inferior vena cava, which causes engorgement of the epidural veins, and engorgement of the epidural veins decreases CSF volume (which causes the higher spread of local anesthetic) - lower
Geriatric patient have:
- (higher/lower) dosing requirement for spinal anesthetics
- (longer/shorter) onset of epidural and spinal anesthesia
- lower
2. shorter
What happens to the duration of local anesthetics in geriatric patients?
unknown
-some sources say shorter, or longer, or no effect
8 contraindications for neuraxial anesthesia
- patient refusal
- infection at the injection site
- a block could lead to possible meningitis or an epidural abscess - severe hypovolemia
- patient wouldn’t tolerate sympathectomy - coagulopathy
- could lead to a possible epidural hematoma - severe aortic stenosis
- Sympathectomy drops preload & afterload, and preload/afterload should be maintained with aortic stenosis - severe mitral stenosis
- sepsis
- Block placement could lead to possible meningitis and/or epidural abscess - elevated ICP
-Patients with increased ICP can’t tolerate the sympathectomy because a high MAP is required to perfuse the head in patients with intracranial hypertension
(Cerebral perfusion pressure = MAP – ICP
4 relative contraindications to neuraxial anesthesia
- neurologic deficiencies
- (MS) - Sepsis
- previous back surgery
- may affect the spread of local anesthetics - severe COPD
- COPD patients rely on accessory muscles to breathe
there is roughly a _____ % incidence of back pain after spinal anesthesia
25%
What are 5 possible etiologies of back pain following a spinal anesthesia?
- common backache from the needle or lying flat too long
- epidural abscess
- epidural/ spinal hematoma
- transient neurologic symptoms
- cauda equina syndrome
_____ is caused by an infection, potentially after back surgery or a neuraxial block
epidural abscess
3 symptoms of an epidural abscess
- back pain intensified by spine percussion
- signs of infection (fever, elevated WBC count
- sensory AND motor deficits
how is an epidural abscess diagnosed and treated?
diagnosed with a CT scan and may require surgical decompression via a lamenectomy
What are the 2 different symptoms that an epidural hematoma produces when compared to an epidural abcess
- shorter onset of symptoms
2. WBC count should be normal
What is the treatment for epidural hematoma?
immediate surgical evacuation
What does a patient experience with Transient neurologic symptoms (TNS)?
back pain WITHOUT motor deficits
- back pain in first 24 hours that resolves on its own
- usually does not require a neuro consult
What does a patient experience in Cauda Equina Syndrome (CES)?
back pain AND motor deficits
- (paresis of the legs) and/or bladder and bowel dysfunction
- The etiology has been linked to nerve root and/or spinal cord trauma, highly concentrated spinal local anesthetics, and continuous spinal anesthesia through a microcatheter
- needs a stat neuro consult
What 2 options does an anesthetist have if they accidentally give the patient a wet tap?
- Thread the catheter ≈2cm intrathecally for continuous spinal anesthesia
- Remove the needle and start another epidural at higher dermatome level
What are the symptoms of a PDPH and what aggravates the pain?
Symptoms include bilateral, frontal, occipital, and extends into the neck
Pain is aggravated by sitting or standing and may last for a few weeks
-The reason is that the pain is aggravated by sitting and standing is that venous return decreases in those positions, and decreased venous return engorges the epidural veins and drives more CSF out (which worsens the symptoms of the headache)
the incidence of PDPH (increases/decreases) with age
decreases
What is the gold standard for PDPH?
blood patch
If a blood patch is attempted before the local spinal anesthetic has worn off, what will happen?
total spinal anesthesia
What 4 other strategies can also treat PDPH?
- caffeine
- analgesics
- steroids
- generous fluid administration
What combo of 2 drugs can treat PDPH and what are the doses?
- Neostigmine (0.02 mg/kg)
2. Atropine (0.01 mg/kg)
What are the 4 benefits of neuraxial anesthesia over general anesthesia?
- decreased anesthetic requirements
- (decreased post op N/V) - decreased respiratory complications
- decreased surgical blood loss
- Decreased incidence of thrombosis (due to decreased platelet aggregation)
Esters:
Have (one/two) “I” in the name
Are metabolized by ______, and produce _____ as a byproduct
Are (more/less) likely to cause allergic reactions than amides
one
-Tetracaine, chloroprocaine, cocaine, Novocaine, etc
plasma esterases
p-aminobenzoic acid (PABA)
more
Amides:
Have (one/two) “i” in the name
Are metabolized by the ____
two
-Bupivacaine, ropivacaine, lidocaine, etc
liver
Local anesthetics (without epi) are slightly (acidic/basic) in the vial they come in
why?
acidic (pH 6-7)
The acidity prolongs the shelf life of the local anesthetic
Local anesthetics are even more (acidic/basic) when epi is added
why?
acidic (pH 4-5)
They have to be more acidic with epi because epi is unstable in basic environments
is tetracaine primarily used in spinals or epidurals?
spinals
What is the longest acting spinal anesthetic?
tetracaine
What does epinephrine do to the duration of tetracaine?
prolongs its duration the longest out of all the local anesthetics
What is the most common local anesthetic we use for spinal anesthesia?
0.75% marcaine (bupivicaine)
What is the duration of 0.75% marcaine?
2 hours
What does epinephrine do to the duration of 0.75% marcaine?
prolonging its duration is the LEAST affected by epi
If a spinal block needs to last more than 2 hours, what local anesthetic should be used?
tetracaine
When would lidocaine be considered in spinal anesthesia?
if the procedure were very short and the anesthetist wanted the spinal to wear off as fast as possible
Why isn’t lidocaine commonly considered for spinal anesthesia?
because its intrathecal use has been associated with transient neurologic symptoms and cauda equina syndrome
What drug is contraindicated in spinal anesthesia?
Chloroprocaine
What are the 4 most common local anesthetics for epidural anesthesia?
- 0.1-0.25% marcaine
- ropivacaine
- lidocaine
- chloroprocaine
What is the most common local anesthetic for labor epidurals?
why?
0.1-0.25% Marcaine
Marcaine is “motor sparing,” meaning that it doesn’t block the motor nerves as well
This is great in OB, because it can provide a sensory block to relieve pain, without blocking the ability of the mother to “push” more effectively during delivery
Which local anesthetic is the LONGEST acting in labor epidurals?
0.1-0.25% marcaine
3 disadvantages to epidural marcaine
- has the lowest onset of all the epidural local anesthetics
- cardiotoxic
- less effective at blocking the larger sacral nerves
- marcaine epidurals have a higher chance of losing their effectiveness during stage two labor
What is the toxic dose of epidural marcaine with epi and without epi?
w/out epi: 2.5 mg/kg
w/epi: 3 mg/kg
What is the treatment for Marcaine/bupivicaine toxicity?
CPR
Intralipid 20%
What is the concentration of epidural ropivicaine (naropin)?
0.2%
What is the difference between marcaine and ropivacaine?
same pharmacology
but ropivacaine is less cardiotoxic and more expensive
What is the maximum dose of ropivacaine?
3 mg/kg
what is the concentration of epidural lidocaine?
2%
OR
1.5% with Epi
What are the 2 advantages of using epidural lidocaine?
- more effective at blocking the larger sacral nerves
- This makes it a great drug to bolus during stage II labor in situations where epidural Marcaine isn’t producing satisfactory analgesia - fast onset
What are the 2 disadvantages of epidural lidocaine?
- produces a more significant motor blockade than marcaine (more concentrated)
- It is therefore more likely to inhibit a parturient from “pushing” effectively during delivery - If the toxic dose is exceeded, the patient can exhibit neurologic symptoms (confusion, tinnitus, oral numbness, and even seizures)
What is the toxic dose of epidural lidocaine?
4mg/kg w/o epi, and 7mg/kg with epi
What is the concentration of epidural chloroprocaine?
2% or 3%
2 advantages of epidural chloroprocaine
- produces the fastest epidural onset (which makes it the perfect choice for bolusing an epidural for an emergency C-section)
- has minimal drug transfer across the placenta
Why does chloroprocaine have the fastest onset?
pseudocholinesterase metabolism
2 disadvantages of epidural chloroprocaine
- produces the highest degree of motor block
- Chloroprocaine is not used for labor analgesia due to its increased motor block - chloroprocaine has the shortest duration
- needs to be re-dosed more frequently
What are the 5 situations in which we would bolus an epidural?
- initial test dose
- loading dose
- dose to increase the blocks density
- raising the block to T4 gradually
- raising the block level to T4 immediately
What are 2 things the anesthetist should do prior to bolusing an epidural?
- verify the patient has stable vital signs in case of sympathectomy
- Aspirate (every time) to rule out intravascular or intrathecal injection
how long should a patient be monitored by anesthesia after an epidural bolus?
10 minutes
what are signs of intravascular injection from an epidural bolus?
fast heart rate (from the epi)
tinnitus (ringing in the ears from the lido)
oral/tongue numbness (from the lido)
What is a sign of intrathecal injection from an epidural bolus?
immediate leg numbness
the initial test dose of an epidural consists of what amount and concentration of mixed local anesthetic?
5mL dose of 1.5% lidocaine with 1:200,000 epi
What amount and local anesthetic is the loading dose?
5 mL of marcaine or ropivacaine
What is the advantage of the epidural loading dose?
speeds up the onset of the block
What is the disadvantage of the epidural loading dose?
it can raise the level of the block above T10 and make a sympathectomy much more likely
When a patient is still experiencing pain after an epidural is placed it is referred to as a _____
How can this be fixed?
patchy block
additional 5 mL of 2% lidocaine
Whenever a laboring patient (who was planning on having a regular vaginal delivery) needs to have a non-emergent C-section, an anesthetist needs to (gradually/ immediately) raise the level of the epidural block to ____
gradually
-needs to be raised gradually because raising the block too rapidly increases the risk that the block could go too high
T4
What are the 3 steps in which an anesthetist gradually raises the epidural block level to T4
- Gives an initial 10mL of local anesthetic, waits 3 minutes, and then checks the dermatome level
- Gives an additional 5mL of local if the block is not high enough, waits 3 minutes, and then checks the dermatome level again
- Gives a final 5mL of local (for a total of 20mL) if the block not high enough
What happens if the local anesthetic is bolused to fast in an epidural?
The risk of high block and hypotension (from sympathectomy) is increased
What happens if the anesthetist waits too long in between epidural boluses?
The block density will increase, but the block won’t rise
When raising an epidural block from T10 to T4, the local anesthetic of choice is probably ____
Why?
lidocaine
-it has a relatively quick onset, but it lasts long enough that it probably wouldn’t need to be redosed during the surgery
Whenever a laboring patient (who was planning on having a regular vaginal delivery) needs to have a emergent C-section, an anesthetist needs to (gradually / immediately) raise the level of the epidural block up to ___
immediately
T4
How does the anesthetist immediately raise the block level to T4 in an emergent C-section?
in a STAT C-section, we bolus 20mL of epidural anesthetic all at once, because we’re willing to risk a high block or sympathectomy in order to have the faster onset
What is the drug of choice for emergency c-sections?
20mL of 3% Chloroprocaine (600 total mg)
-has the fastest onset, and in an emergency, the last thing we care about is whether or not we will have to redose the epidural in the middle of the C-section
_____ any kind of vial that may be used more than once and generally contains antibacterial preservatives
multiple-dose vial (MDV)
_____ is intended to be used only once and contains no preservatives
single-dose container
3 common preservatives in local anesthetics
- Sulfites (bisulfite, metabisulfite)
- Parabens (methylparaben)
- EDTA
_____is a bacteriostatic preservative that is commonly added to multidose vials of local anesthetics
methylparaben
-Sensitive patients may experience anaphylactoid symptoms
_____ preservatives are contraindicated for both epidural and intrathecal administration
methylparaben
_____(along with citric acid) are added to local anesthetics that come premixed with epinephrine (or any other vasoconstrictor) in order to “prevent the degradation of epinephrine in an alkaline pH
sulfites
The resulting acidic solution tends to cause more pain on injection
Freshly mixed solutions of lidocaine with epinephrine (by an anesthetist) result in a less acidic solution; therefore less discomfort with injection
the sulfite (epinephrine stabilizing) preservatives are safe for (epidural/ spinal/ both)
epidural only
_____ has been added to local anesthetics in the past to prolong shelf life and enable the manufacturer to use an autoclave to sterilize the glass vial containing the local anesthetic. It also acts as a chelating agent
EDTA
What happens when EDTA is injected epidurally?
severe pain at the injection site but no evidence of neurotoxicity
What happens when sulfate is injected intrathecally?
development of arachadonitis, and administration of sulfites in general is capable of inducing anaphylactoid reactions
What are the 2 things the anesthetist should check on the local anesthetic vial before injecting into the intrathecal space or epidural space?
- preservative free
2. “for epidural or spinal use”
why should IV regional anesthesia like Beir blocks use preservative free local anesthetic?
to avoid irritation and anaphylaxis
Why is bicarb added to lidocaine or chloroprocaine?
to speed up the onset and bring the pH of the drug closer to its pKa
-Mostly when raising the block level from T10 to T4
that bicarb causes the local anesthetic to precipitate within ____
6 hours
what 3 things do alpha agonists do to local anesthetic blocks?
- Prolongs block duration
- Limits toxic side effects
- Enhances analgesic quality
If a local anesthetic is more lipid soluble, the advantage of adding epinephrine to the local anesthetic is (more/less) significant
less
Which of the local anesthetics does epinephrine have the least effect on the duration?
bupivacaine
-it’s highly lipid soluble
With what drug does the alpha agonist not apply for lipid soluble duration?
tetracaine
-epinephrine has the greatest effect on the duration of tetracaine, even though tetracaine has a higher lipid solubility than bupivacaine
What do alpha agonists do to local anesthetics in addition to prolonging the duration?
cause potent analgesia by directly inhibiting sensory and motor neurons
____ is associated with a greater decrease in blood pressure in some studies, and can prolong block duration even when administered orally
clonidine
morphine without preservatives
duramorph
-which allows dosing in the intrathecal space
Morphine causes (more/less) respiratory depression in fetus than fentanyl
more
Intrathecal/epidural/intravenous morphine carries a (higher/lower) risk of urinary retention when compared to fentanyl
higher
3 advantages of neuraxial opiods
- analgesia
- no motor blockade
- no sympathectomy
3 disadvantages of neuraxial opiods
- puritis
- delayed respiratory depression
- This is more likely to occur following intrathecal morphine than intrathecal fentanyl, due to the fact that Morphine is less lipid soluble than Fentanyl - nausea/ vomiting
What is the most common complication of neuraxial opiods?
puritis
When should narcotics not be added to a spinal?
spinal if the procedure is outpatient
-There is a risk of exaggerated respiratory depression if the patient takes their PO narcotics at home before the spinal opioids have worn off
2 advantages to using precedes (dexmedetomidine)
- sensory blockade was longer
2. similar analgesia and less pruritus and shivering compared with morphine
The more polar a drug is, the ____ the onset
slower
If an acidic drug is placed in a basic environment (less protons, higher pH), it will become _____charged,
negatively
-because the drug will donate protons to the environment
If a basic drug is placed in an acidic environment (more protons, lower pH), it will become _____ charged,
positively
-because the environment will donate protons to the drug
If the drug is placed in an environment with an “ideal pH,” it will have the highest nonpolar portion and the (fastest/slowest) onset
fastest
This “ideal pH” for the drug (the pH of the drug’s environment that will result in 50% ionization and 50% nonionization (which leads to the highest nonpolar portion possible) is referred to as the drug’s pKa
We can speed up onset time by changing the ____ of the drug vial to get closer to the ____ of the drug
pH
pKa
Acidic drugs have a (high/low) pKa
Basic drugs have a (high/low) pKa
low
high
The closer a drug’s pKa is to physiologic pH (7.4), the (less/more) polar it will be in the body, and the (faster/ slower) onset it will have
less
faster
local anesthetics by themselves are (basic/acidic)
basic
local anesthetics in the vial are (basic/acidic)
acidic
-prolongs the shelf life
Epinephrine containing solutions have a pH that is ____ units lower than the pH of plain solutions
1-1.5
The pH of a drug solution is 4.5. The pKa of the drug is 10.7. Adjusting the pH of the drug to ____ will result in the fastest onset
- 5
- 0
- 4
- 7
10.7
A drug solution has a pH of 6.5 and a pKa of 5.5. Adjusting the pH of the drug closer to physiologic pH will speed up the drug onset.
True or false?
false
local anesthetics with a high lipid solubility with have a
- (faster/slower) onset
- (shorter/ longer) duration
- (incrased/decreased potency)
- slower
- longer
- increased
other drugs (fentanyl) with high lipid solubility have a
- (faster/slower) onset
- (shorter/ longer) duration
- (incrased/decreased potency)
- faster
- shorter
- increased
