1. Neuraxial Anesthesia & Local Anesthetic Dosing Flashcards
(264 cards)
1
Q
adult spinal cord end
A
L1-L2
2
Q
conus medullaris
A
end of spinal cord
3
Q
cauda equina
A
nerve root bundle that begins at the conus medullaris
4
Q
cauda equina innervates
A
legs and bladder
5
Q
adult dural sac end
A
S2
6
Q
kid spinal cord end
A
L2-L3
7
Q
kid dural sac end
A
S3
8
Q
layers from skin to CSF 7
A
1 skin 2 supraspinous ligament 3 interspinous ligament 4 ligamentum flavum 5 epidural space 6 dura mater 7 subarachnoid space
9
Q
lordosis (convex) is where in spine
A
cervical 7
lumbar 5
10
Q
kyphosis (concave) is where in spine
A
thoracic 12
11
Q
kyphosis
A
posterior curvature of spine
12
Q
lordosis
A
anterior curvature of the spine
13
Q
scoliosis
A
lateral curvature of the spine
14
Q
how many cervical vertebrae
A
7
15
Q
how many thoracic vertebrae
A
12
16
Q
how many lumbar vertebrae
A
5
17
Q
how many sacral vertebrae
A
5
18
Q
how many coccygeal vertebrae
A
4
19
Q
how many total vertebrae
A
33
20
Q
how many cervical nerve roots
A
8 pairs
21
Q
how many thoracic nerve roots
A
12 pairs
22
Q
how many lumbar nerve roots
A
5 pairs
23
Q
how many sacral nerve roots
A
5 pairs
24
Q
how many coccygeal nerve roots
A
1 pair
25
how many pairs of spinal nerve roots total
31
26
what are nerve roots covered by
dural sheath
27
why is it important that nerve roots are covered by dural sheath? 2
1. roots close to spinal cord float in dural sac and pushed away by advancing needle
2. nerve blocks close to intervertebral foramen carry risk of subdural injection
28
what is the most common starting insertion site for a spinal or lumbar epidural?
L3-4 interspace
| L4-5 is acceptable; L2-3 may be considered if lower attempts fail
29
tuffiers line
line between superior aspects of iliac crests and estimates L4 body
30
what is the T10 (umbilicus) dermatome needed for? 3
1 spontaneous vaginal delivery (SVD)
2 inguinal surgery
3 testicular surgery
31
what is the T4 (nipple) dermatome needed for?
c-section
32
why is it convenient that T4 is the most dependent area of the spine in the supine position?
lay pts down after spinal then it will go to the correct height usually
it helps prevent the spread of local anesthetic above T4 and prevents high spinal
33
T5-L1
vasomotor tone
34
what happens when T5-L1 are blocked with spinal or epidural
vasodilation and hypotension
"sympathectomy"
nearly all pts with spinals in supine position will have a degree of sympathectomy
35
are sympathectomies more common with spinals or epidurals?
spinals
36
what is the earliest sign of sympathectomy?
nausea and vomiting
37
T1-T4
cardiac accelerator fibers
38
what can happen if the block rises above T4?
significant bradycardia bc you are blocking the sympathetics to the heart
39
C3-C5
phrenic nerve
| if the block goes above this then the pt will go apneic
40
C6-C8
hands/fingers
| the pt will experience tingling/numbness or weakness in their fingers
41
what do you do if they start to get numbness in their fingers?
place the pt in reverse trendelenburg
42
T4-T5
carina
43
T6
xyphoid process
44
T7
inferior border of scapulae
45
T8-L1
kidney
46
S2-S4
bladder
47
sympathetic blockade
blocking the nerves up to that level will have the ability to produce hypotension and bradycardia
48
sensory blockade
blocking nerves up to that level will produce an absence of pain but NOT of movement/touch
49
motor blockade
blocking nerves up to that level will block the pts ability to move those limbs
50
levels of sympathetic vs sensory vs motor blockade
sympathetic is two levels higher than sensory
| sensory is two levels higher than motor
51
nerves are more easily blocked if they are: 2
1 smaller
| 2 myelinated
52
differential blockade order from easiest to hardest block
autonomic>sensory>motor
53
what is the goal of an epidural?
to stop the needle in the epidural space and not puncture the dura
54
what type of needle is used for an epidural?
17ga tuohy needle
55
4 epidural advantages
1 we can give analgesia as long as necessary
2 more control over analgesic level
3 less profound sympathectomy
4 better preservation of motor function is possible (less dense block)
56
disadvantages to epidural
1 not as dense as spinal (not as comfortable if they have to do a c-section)
2 high propability of PDPH (headache) if needle puncture
3 onset of action is longer for epidurals (several minutes)
4 more potential for local anesthetic toxicity with epidural
57
walking epidural
epidural where it is either:
only narcs
lower dose local
-it preserves motor function, good for post op pain control
58
spinal anesthesia description (3)
1 dura punctured
2 single shot of drug given (preservative free)
3 smaller needles are used
59
two spinal pencil point needles
whitacre
sprotte
| sprotte
60
whitacre needle
smallest opening
| CSF aspiration slow and hard
61
sprotte needle
longer opening
CSF aspiration easier
higher chance of injecting epidurally
62
spinal cutting type needle
quincke
63
quincke
cuts through ligaments better but makes larger hole in dura
64
what is the 18ga introducer needle used for
the spinal needle can be placed through the introducer to guide it to the correct spot
65
advantage of introducer needle
much less bending of spinal needle
| commonly used if spinal needle is smaller than 22ga
66
22ga spinal needle advantage and disadvantage
advantage-
18ga introducer not needed
disadvantage-
higher risk of spinal headache
67
common uses for the 22ga spinal needle
```
elderly pts (lower risk of headache)
obese pts
```
68
advantage to 25ga spinal needle
way less likely for spinal headache
69
what is the most common size spinal needle for adults?
25ga
70
disadvantage to 25ga spinal needle
more likely to bend when passing ligaments ** used with introducer
71
advantage to 27ga spinal needle
smallest hole in dura and least likely headache
72
disadvantage to 27ga spinal needle
highest chance of bending through ligaments
73
when is the 27ga spinal needle used?
CSE
| combined spinal epidural where it is placed through the espocan needle
74
continuous spinal anesthesia
catheter placed into intrathecal space
75
problem with continuous spinal anesthesia
microcatheter use for continuous spinal anesthesia is contraindicated due to pooling of local anesthetic
76
what is the risk associated with microcatheters
neurotoxicity and cauda equina syndrome
| pooling of local anesthetic
77
practical use of continuous spinal anesthesia
problem: accidentally wet tap someone during epidural placement
fix: just thread epidural catheter into the intrathecal space through touhy needle and give lower doses
78
4 management steps of continuous spinal anesthesia
1 sterile technique critical
2 catheter threaded 2-3cm intrathecal space
3 analgesia is usually maintained with local anesthetic boluses NOT infusion
4 appropriate dosing intervals are anywhere from 45-90 min
79
what should you do before and after each continous spinal injection
flush with previously aspirated CSF after each injection
80
baricity
how dense (heavy) the drug is compared to CSF and the density determines whether the drug will sink or rise
81
3 types of baricity
hyperbaric
hypobaric
isobaric
82
hyperbaric
spinal drug is denser than CSF and drug will sink
83
how to make drug hyperbaric
adding an equal volume of 10% dextrose/glucose to the local anesthetic
84
where does a hyperbaric spinal move when placed in supine pt
the hyperbaric drug tends to move to T4 because it is the most dependent area of the spine
85
how do we know that glucose must interfere with the hyperbaric drugs absorbtion?
shorter time to peak concentration
| shorter duration of action than plain local anesthetics
86
what happens if you allow pt to remain sitting after placing a hyperbaric spinal?
saddle block anesthetizes:
sacral nerves
buttocks
perineal
thighs
87
what does a saddle block anesthetize?
sacral nerves
buttocks
perineal area
inner thighs
88
what types of procedures are saddle blocks used for
genitourinary
| 2nd stage labor pain
89
hypobaric drug
spinal drug is lighter than CSF and drug will rise
90
how do you make a drug hypobaric
add sterile water
91
how much sterile water do you add to a drug to make it hypobaric
depends on source!!
larger volume
3mL per 1mL
1mL per 1mg
92
what is the most common use for a hypobaric spinal?
hip surgery
| pt in lateral position with operative hip up
93
isobaric spinal drug definition
spinal drug has the same specific gravity as CSF and will remain at the level of injection
94
how do you make a drug isobaric?
add equal volume of CSF or normal saline to the local
95
does baricity apply to spinals and epidurals?
no just spinals
96
how long until the baricity of the spinal settles?
10-15min
| then shouldn't rise or sink based on position
97
CSE
combined spinal epidural technique
98
CSE technique (6 steps)
1 touhy needle placed in epidural space
2 27ga spinal needle through touhy into the intrathecal space
3 perform spinal block into intrathetcal space
4 remove spinal needle
5 thread epidural catheter through touhy needle
6 remove touhy needle
99
what is a common needle set for the CSE?
espocan kit
17 ga tuohy needle with hole
27ga spinal needle
100
advantages CSE 3
1 more dense block than epidural
2 decr risk of PDPH
3 postop analgesia with epidural w/o using duramorph
101
disadvantage to the CSE
can't perform a test dose through the epidural catheter bc the pt is already numb from the spinal
102
dural puncture epidural technique 5
1 17ga epidural needle placed
2 spinal needle though tuohy and punctures dura
3 spinal needle removed without dosing
4 epidural catheter placed into epidural space
5 some of the local anesthetic leaks into the intrathecal space through the small hole
103
advantages to dural puncture epidural technique 3
1 faster sacral onset
2 greater sacral spread of local
3 lower incidence of unilateral block
104
disadvantage dural puncture epidural technique
small chance of post dural puncture headache
105
epidural summary points
longer analgesia possible
more control of analgesic level
more gradual, less profound sympathectomy
less dense block
106
spinal summary points
limited analgesic duration
single shot (cant alter dose)
rapid potent sympathectomy
denser block
107
sacral hiatus
site of needle insertion for caudal block
108
what is the sacral hiatus covered by?
sacrococcygeal ligament
109
sacral cornu
bony pominence to either side of sacral hiatus
| palpate these for landmarks
110
is a caudal block a spinal or epidural?
epidural block but differs because
performed at sacral level
dosed with single shot of drug
111
caudal block technique 5
1 palpate sacral hiatus
2 insert needle through sacral hiatus at 45 deg angle
3 advance cephalad until pop
4 advance cannula over the needle and remove needle
5 aspirate before inject
112
when is it possible for the epidural to cause spinal cord or nerve root damage?
in the lumbar or thoracic region
113
what will happen when epidural needles get too close to nerve roots?
patients experience parasthesias and the anesthetist can redirect
114
can lumbar and thoracic epidurals be done when the patient is asleep?
no they must be awake to reduce the risk of nerve injurt
115
can caudal blocks be done when the patient is asleep?
yes because they are so far away from the spinal cord or roots
116
what is the most popular block for children?
caudal block
117
3 advantages to caudal blocks
performed on asleep pts
more reliable perineal anesthesia (than lumbar)
less likely dural puncture and nerve damage
118
5 disadvantages to caudal blocks
```
dural can still be punctured
rectum can be punctured
technically more difficult in adults
twice as much local anesthetic required than lumbar epidural
higher risk of urinary retention
```
119
8 factors that affect neuraxial spread of local anesthetics
```
1 total mg dose
2 total volume injected
3 addition of epi
4 addition of narcotic
5 height of patient
6 positioning
7 weight of patient
8 age
```
120
how does total mg dose affect spread?
higher doses spread more
121
how does volume injected affect spread
the higher volume will spread more
122
does dose or volume have greater affect on spread
dose
123
how does the addition of epi spread the block?
it prolongs the block but doesnt raise the level
124
how does addition of narcotic affect the block
increases the density "strength" of the block
125
how does the height of the patient affect the block
the shorter you are the more likely it will travel too high
126
how does trendelenburg effect block
more cephalad spread of local
127
how does reverse trendelenburg effect block
less cephalad spread of local
128
how does lateral effect block
block will be more one sided
129
how does the weight of the patient effect spread of block
the more obese (heavy) the patient: higher it will spread and a lower local dose is required
130
why does local anesthetic spread higher in heavier patients?
increased intraabdominal pressure
compression of inferior vena cava
engorgement of epidural veins
decreases CSF volume
131
how does age effect spread of block
geriatric pts have: lower dosing requirements and shorter onset (reduced CSF volume; decrease in nerve fibers and decreased conduction velocity)
132
8 absolute contraindications to neuraxial anesthesia
```
1 refusal
2 infection at injection site
3 serve hypovolemia
4 coagulopathy (epidural hematoma)
5 severe aortic stenosis
6 severe mitral stenosis
7 sepsis
8 elevated ICP
```
133
what could infection at injection site or sepsis lead to
meningitis or epidural abscess
134
what must the platelet count be for OB before neuraxial blockade?
>80,000- 100,000
135
why should aortic/mitral stenosis be avoided with neuraxial blocks?
sympathectomy drops preload and afterload and those should be maintained with aortic stenosis
136
why avoid neuraxial block in patients with elevated ICP?
cant tolerate sympathectomy
high MAP is needed to perfuse the head with elevated ICP
Cerebral perfusion pressure= MAP-ICP
137
relative contraindications for neuraxial anesthesia 4
1 neurologic deficiencies (MS) (worsening symptoms)
2 sepsis
3 previous back surgery (may effect spread)
4 severe COPD (may rely on accessory muscles to breath)
138
11 potential complications of neuraxial blocks
```
pruritus
nausea and vomiting (from hTN)
urinary retention
parasthesia (short term)
nerve/ spinal cord injury
backache
PDPH
transient neurologic symptoms (TNS)
cauda equina syndrome (CES)
epidural abscess
epidural hematoma
```
139
what is the incidence of back pain following spinal anesthesia?
25%
140
possible etiologies of back pain: 5
```
1 regular common backache from needle or lying flat
2 transient neurologic symptoms (TNS)
3 cauda equina syndrome (CES)
4 epidural abscess
5 epidural/spinal hematoma
```
141
what is a epidural abscess caused by
infection potentially after back surgery or neuraxial block
142
what are the symptoms of a epidural abscess
back pain intensified by spine percussion
signs of infection (fever, increases WBC)
sensory AND motor deficits
143
how is an epidural abscess diagnosed?
ct scan
144
treatment of epidural abscess
surgical decompression via laminectomy
145
how are the symptoms of epidural abscess and epidural hematoma different?
hematoma has faster onset and the WBC count should be normal
146
how are epidural hematomas treated
immediate surgical evacuation
147
what is transient neurologic symptoms?
someone who experiences back pain without motor deficits
| resolves on own
148
what are some hypothesis about what causes TNS
lithotomy position
intrathecal vasoconstrictors
highly concentrated local
lidocaine
149
which is more serious CES or TNS?
CES because it includes back pain and motor deficits and/or bladder and bowel dysfunction
150
etiology of CES
nerve root/spinal cord trauma
highly concentrated local anesthetics
continuous spinal anesthesia through microcatheter
151
which needs a neurology consult? CES or TNS
CES
152
post dural puncture headache
more likely to occur with wet tap from tuohy needle during epidural
less likely with spinal because headache is proportional to the size of the hole
153
if someone gets a wet tap what is the likelihood of PDPH
80% chance
154
what are the two options for if you wet tap a patient
thread catheter ~2cm intrathecally for continuous spinal anesthesia
remove needle and start another epidural higher level
155
if you are older are you more or less likely to get a PDPH?
less likely as you get older
156
symptoms of PDPH
headache bilateral frontal occipital and extends to neck
| aggravated by standing or sitting
157
why does standing make the headache worse
venous return decrease
epidural veins engorge
push out more CSF and worsen the headache
158
3 treatments for PDPH
autologous blood patch
analgesics, caffeine, generous fluid admin
neostigmine and atropine combination
159
what is the gold standard for PDPH treatment
blood patch, 90-99 success rate
160
regional anesthesia advantages (compared to GA) 4
1 decreases anesthetic requirements (decreases postop N/V)
2 decrease respiratory complications
3 decreased surgical blood loss
4 decreases incidence of thrombosis
161
how many "i" in esters
one
162
how many "i" in amides?
more than one "i"
163
how are esters metabolised
plasma esterases
164
what do esters produce as a byproduct and why does that matter
p-aminobenzoic acid PABA
| it is associated with allergic reactions
165
how are amides metabolized?
by the liver
166
which is more likely to cause an allergic reaction? tetracaine or marcaine?
tetracaine because it is an ester
167
what is the pH of local without epi
6-7
| acidic so it prolongs shelf life
168
what is the pH of local with epi
4-5
| more acidic because epi is unstable in basic environments
169
what local is the longest acting spinal local?
tetracaine (pontocaine)
170
which drug is the most common for spinal anesthesia
marcaine 0.75%
171
which local's duration is least affected by addition of epi?
marcaine
172
marcaine duration
2 hours
173
how long does adding phenylephrine to tetracaine increase the duration of block
70-100%
174
how long does adding epi to tetracaine increase the duration of block
40-60%
175
how long does adding clonidine to tetracaine increase the duration of block
50-70%
176
which spinal local promotes early ambulation?
spinal mepivacaine
177
which spinal local is best for ultra short procedures?
spinal chloroprocaine
178
which spinal local is associated with TNS and CES
lidocaine
179
what are the 4 most common local anesthetics for labor epidural dosing
marcaine
ropivacaine
lidocaine
chloroprocaine
180
marcaine advantages 2
motor sparing
longest duration of epidural locals
| longest lasting
181
marcaine disadvantages 3
1 less effective at blocking the larger sacral nerves
2 slowest onset
3 very cardiotoxic
182
what is the implication of marcaine being less effective at blocking larger sacral nerves
higher chance of losing their effectiveness during stage two labor
183
toxic dose marcaine with and without epi
2.5mg/kg w/o epi
| 3mg/kg w/ epi
184
what is the treatment for marcaine toxicity
CPR
| intralipid 20%
185
Ropivacaine (naropin) 0.2%
similar pharmacology to marcaine
| less cardiotoxic and more expensive
186
what is the max dose of ropivacaine
3mg/kg
187
advantages of lidocaine 2% or 1.5% with epi
more effective at blocking larger sacral nerves
| fast onset
188
disadvantages of lidocaine 2% or 1.5% with epi
more significant motor blockade (could inhibit pushing)
neurologic symptoms if the toxic dose is exceeded
highest risk of TNS and CES (intrathecal hyperbaric lido)ch
189
what is the toxic dose of lidocaine with epi
7mg/kg
190
what is the toxic dose of lidocaine without epi
4mg/kg
191
chloroprocaine (3%) advantages
fastest epidural onset
| minimal drug transfer across placenta
192
when are you most often going to use chloroprocaine
emergency c section
193
why does chloroprocaine have such a rapid onset
pseudocholinesterase metabolism
194
chloroprocaine 3% disadvantages
```
highest degree of motor block
shortest duration (redosed frequently)
```
195
which local should you use for vaginal delivery?
marcaine
196
which local should you use if epidural stops working
lidocaine
197
198
5 most common situations an epidural is bolused include
```
initial test dose
loading dose
dose to increase blocks density
raising the block to t4 gradually
raising the block to t4 immediately
```
199
what should you do before bolusing an epidural?
verify they have stable vital signs prior to bolusing and monitor for 10 mins after
aspirate everytime to rule out intravascular or intrathecal injection
200
signs of intravascular injection
increase HR
tinnitus
oral/tongue numbness
201
sings of intrathecal injection
immediate numbing of the legs
202
what is the initial test dose
5mL of 1.5% lido with 1:200,000 epi
203
accidental IV injection ruled out by absence of:
tachycardia
mouth/tongue numbness
ringing in ears
204
accidental intrathecal injection ruled out by
not having immediate numbness
205
epidural loading dose
additional 5mL loading dose after test dose to speed up the onset of block
higher risk of sympathectomy
206
why dose to increase the density of epidural block ?
patchy block when it starts to wear off, disconnect pump and bolus 5mL
207
when would you raise the epidural block gradually to t4?
non emergent c section
208
how to raise the epidural block level gradually
gives initial 10mL of local, wait 3 min check level
give 5mL of local, wait 3 min, check level
give another 5mL of local if still not high enough
209
if local is bolused too fast what will happen
risk of high block and hypotension is increased
210
if the anesthetist waits too long in between boluses what happens?
the block density will increase but the block wont rise
211
what is the local of choice for raising an epidural block from t10 to t4?
lidocaine has longer duration than chloroprocaine
Chloroprocaine is faster onset
212
what are common preservatives in local anesthetics?
sulfites (bisulfite, metabisulfite)
parabens (methylparaben)
EDTA
213
do multi dose or single dose vials have preservatives?
multidose vials
214
methylparaben
bacteriostatic preservative added to multidose vials
| potential anaphylactoid symptoms
215
what is methylparaben contraindicated for?
epidural and intrathecal
216
what are methylparaben free solutions referred to as?
MPF
217
sulfites (and citric acid) are added to what?
local that are premixed with epi to prevent degradation of epi
causes more pain on injection
218
what has intrathecal injection of sulfites resulted in?
arachadonitis
| anaphylactoid rxns
219
what are sulfites contraindicated for?
spinals
220
are sulfites okay to use for epidurals?
yes
221
what is EDTA used for?
prolong shelf life and allow autoclaving to sterilize glass vial
222
what is EDTA been linked to in patients?
epidurally injected associated with severe pain at injection site
223
can you use chloroprocaine for spinals?
yes
recently approved by FDA
224
what two things should you check before injecting epudural or intrathecal
preservative free
| "for spinal or epidural use"
225
can you use a local with preservatives for a bier block?
no
226
why is bicarb added?
added to lidocaine or chloroprocaine to speed up onset by bringing closer to pKa
227
how long until the local will precipitate when bicarb is added
6hr
228
effects of adding alpha agonist?
prolongs block duration
limits toxic side effects
enhances analgesic quality
229
what local is effected the most with added epi
tetracaine
230
what local is effected the least with added epi
bupivacaine
231
if the local is _____ lipid soluble then added epi is less significant.
more
232
can alpha agonists cause analgesia?
yes by directly inhibiting sensory and motor neurons
233
what does clonidine do to BP
greater decrease in BP
234
duramorph
morphine without preservatives
235
which causes more respiratory depression in fetus and urinary retention? morphine or fentanyl?
morphine
236
advantages of neuraxial opioids
analgesia
no motor blockade
no sympathectomy
237
disadvantages of neuraxial opioids
pruritus (itch)
delayed respiratory depression
nausea/vomiting
238
the more lipid soluble drugs they have a _____ onset and _____ duration
faster onset
| shorter duration
239
____ lipid soluble drugs exit the central nervous system quickly
more
240
duration of epidural narcotics
twice as long as spinal because epidural dose is higher
241
spinal dosing of opioids
should not be dosed if it is outpatient procedure
242
what are the three forms a drug can be in?
non polar
polar/neg charged (loss of H+)
polar/pos charged (gain of H+)
243
what is the form a drug takes determined by? 2
drugs pH
| pH of environment the drug is placed in
244
if you have higher degree of nonpolar drug then the onset is
faster
245
do the ionized or nonionized portion of the drug cross the lipid membrane?
nonpolar (nonionized)
246
if an acidic drug is placed in a basic environment then it will become:
negatively charged and slow the onset of the drug
247
if a basic drug is placed in an acidic environment then it will become
positively charged and it will slow the onset of the drug
248
what is the highest possible portion of nonpolar drug
50%
249
when you place a drug in an ideal pH then it will
have the highest portion of nonpolar drug and fastest onset possible
250
pKa
pH of the drugs environment that will result in the drug having 50% ionization and 50% nonionization
251
pH of lidocaine
6.5
252
pKa of lidocaine
7.9
253
what would you do to bring the pH of lidocaine closer to its pKa?
add sodium bicarb
254
do basic drugs have a high or low pKa
high
255
do acidic drugs have a high or low pKa
low
256
the drug will have a ____ onset the closer the drugs pKa is to physiologic pH 7.4
faster
257
are local anesthetics by themselves more acidic or basic?
basic
258
are local anesthetics in the vial more acidic or basic?
acidic
| acid added so it wont precipitate
259
adding bicarb to local anesthetic will 4
1 bind up excess acid
2 make drug less pos charged
3 increase the pH
4 speed up onset of action
260
how much lower is the pH of local when the solution contains epi?
1-1.5 units lower
261
factors that determine the onset of local anesthetic 4
how ionized the local is
how close locals pH is to the pKa
how close the locals pKa is to physiologic pH
how lipid soluble the local is
262
effect of higher lipid solubility on local anesthetics onset and duration
slow onset
| long duration
263
effect of higher lipid solubility on other drugs such as fentanyl onset and duration
fast onset
| short duration
264
factors that determine local anesthetic potency 3
```
how concentrated (more=potent)
how lipid soluble (higher=potent)
total dose (more=potent)
```
