Neuraxial Anesthesia & Local Anesthetic Dosing Flashcards
1
Q
adult spinal cord end
A
L1-L2
2
Q
adult dural sac end
A
S2
3
Q
kid spinal cord end
A
L2-L3
4
Q
kid dural sac end
A
S3
5
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
6
Q
lordosis (convex) is where is spine
A
cervical 7
lumbar 5
7
Q
kyphosis (concave) is where in spine
A
thoracic 12
8
Q
kyphosis
A
posterior curvature of spine
9
Q
lordosis
A
anterior curvature of the spine
10
Q
scoliosis
A
lateral curvature of the spine
11
Q
how many cervical vertebrae
A
7
12
Q
how many thoracic vertebrae
A
12
13
Q
how many lumbar vertebrae
A
5
14
Q
how many sacral vertebrae
A
5
15
Q
how many coccygeal vertebrae
A
4
16
Q
how many total vertebrae
A
33
17
Q
how many cervical nerve roots
A
8 pairs
18
Q
how many thoracic nerve roots
A
12 pairs
19
Q
how many lumbar nerve roots
A
5 pairs
20
Q
how many sacral nerve roots
A
5 pairs
21
Q
how many coccygeal nerve roots
A
1 pair
22
Q
how many pairs of spinal nerve roots total
A
31
23
Q
what are nerve roots covered by
A
dural sheath
24
Q
why is it important that nerve roots are covered by dural sheath? 2
A
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
25
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
26
tuffiers line
line between superior aspects of iliac crests and estimates L4 body
27
what is the T10 (umbilicus) dermatome needed for? 3
1 spontaneous vaginal delivery (SVD)
2 inguinal surgery
3 testicular surgery
28
what is the T4 (nipple) dermatome needed for?
c-section
29
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
30
T5-L1
vasomotor tone
31
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
32
are sympathectomies more common with spinals or epidurals?
spinals
33
what is the earliest sign of sympathectomy?
nausea and vomiting
34
T1-T4
cardiac accelerator fibers
35
what can happen if the block rises above T4?
significant bradycardia bc you are blocking the sympathetics to the heart
36
C3-C5
phrenic nerve
| if the block goes above this then the pt will go apneic
37
C6-C8
hands/fingers
| the pt will experience tingling/numbness or weakness in their fingers
38
what do you do if they start to get numbness in their fingers?
place the pt in reverse trendelenburg
39
T4-T5
carina
40
T6
xyphoid process
41
T7
inferior border of scapulae
42
T8-L1
kidney
43
S2-S4
bladder
44
sympathetic blockade
blocking the nerves up to that level will have the ability to produce hypotension and bradycardia
45
sensory blockade
blocking nerves up to that level will produce an absence of pain but NOT of movement/touch
46
motor blockade
blocking nerves up to that level will block the pts ability to move those limbs
47
levels of sympathetic vs sensory vs motor blockade
sympathetic is two levels higher than sensory
| sensory is two levels higher than motor
48
nerves are more easily blocked if they are: 2
1 smaller
| 2 myelinated
49
differential blockade order from easiest to hardest block
autonomic>sensory>motor
50
what is the goal of an epidural?
to stop the needle in the epidural space and not puncture the dura
51
what type of needle is used for an epidural?
17ga tuohy needle
52
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)
53
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
54
walking epidural
epidural where it is either:
only narcs
lower dose local
-it preserves motor function, good for post op pain control
55
spinal anesthesia description (3)
1 dura punctured
2 single shot of drug given (preservative free)
3 smaller needles are used
56
two spinal pencil point needles
whitacre
| sprotte
57
whitacre needle
smallest opening
| CSF aspiration slow and hard
58
sprotte needle
longer opening
CSF aspiration easier
higher chance of injecting epidurally
59
spinal cutting type needle
quincke
60
quincke
cuts through ligaments better but makes larger hole in dura
61
what is the 18ga introducer needle used for
the spinal needle can be placed through the introducer to guide it to the correct spot
62
advantage of introducer needle
much less bending of spinal needle
| commonly used if spinal needle is smaller than 22ga
63
22ga spinal needle advantage and disadvantage
advantage-
18ga introducer not needed
disadvantage-
higher risk of spinal headache
64
common uses for the 22ga spinal needle
```
elderly pts (lower risk of headache)
obese pts
```
65
advantage to 25ga spinal needle
way less likely for spinal headache
66
what is the most common size spinal needle for adults?
25ga
67
disadvantage to 25ga spinal needle
more likely to bend when passing ligaments ** used with introducer
68
advantage to 27ga spinal needle
smallest hole in dura and least likely headache
69
disadvantage to 27ga spinal needle
highest chance of bending through ligaments
70
when is the 27ga spinal needle used?
CSE
| combined spinal epidural where it is placed through the espocan needle
71
continuous spinal anesthesia
rare
| catheter into intrathecal space and repeated doses given
72
problem with continuous spinal anesthesia
microcatheter must be used bc the needles are so small
73
what is the risk associated with microcatheters
neurotoxicity and cauda equina syndrome
| pooling of local anesthetic
74
practical use of continuous spinal anesthesia
accidentally wet tap someone and just thread the catheter into the intrathecal space and give lower doses
75
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
76
what should you do before and after each injection
flush with previously aspirated CSF after each injection
77
baricity
how dense (heavy) the drug is compared to CSF and the density determines whether the drug will sink or rise
78
3 types of baricity
hyperbaric
hypobaric
isobaric
79
hyperbaric
spinal drug is denser than CSF and drug will sink
80
how to make drug hyperbaric
adding an equal volume of 10% dextrose/glucose to the local anesthetic
81
hyperbaric spinal for supine position
the hyperbaric drug tends to move to T4 because it is the most dependent area of the spine
82
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
83
hyperbaric saddle block pt position
allow pt to remain sitting for several minutes after spinal medication
84
what does a saddle block anesthetize?
sacral nerves
buttocks
perineal area
inner thighs
85
what types of procedures are saddle blocks used for
genitourinary
| 2nd stage labor pain
86
hypobaric drug
spinal drug is lighter than CSF and drug will rise
87
how do you make a drug hypobaric
add sterile water
88
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
89
what is the most common use for a hypobaric spinal?
hip surgery
| pt in lateral position with operative hip up
90
isobaric spinal drug definition
spinal drug has the same specific gravity as CSF and will remain at the level of injection
91
how do you make a drug isobaric?
add equal volume of CSF or normal saline to the local
92
does baricity apply to spinals and epidurals?
no just spinals
93
how long until the baricity of the spinal settles?
10-15min
| then shouldn't rise or sink based on position
94
CSE
combined spinal epidural technique
95
CSE technique 4
1 advance CSE tuohy needle into epidural
2 27ga spinal needle through into the intrathecal space perform spinal block
3 thread epidural catheter
4 spinal for operative anesthesia, epidural for postop
96
what is a common needle set for the CSE?
espocan kit
tuohy needle with hole
27ga spinal needle
97
advantages CSE 3
1 denser block for procedure than just epidural
2 use the smallest spinal needle and smaller chance of headache
3 postop analgesia with epidural in case dont want to use duramorph in spinal
98
disadvantage to the CSE
can't perform a test dose through the epidural catheter bc the pt is already numb from the spinal
99
dural puncture epidural technique 5
1 epidural needle placed
2 spinal needle though tuohy and punctures dura
3 spinal needle removed without dosing
4 epidural catheter placed
5 some of the local anesthetic leaks into the intrathecal space through the small hole
100
advantages to dural puncture epidural technique 3
1 faster sacral onset
2 greater sacral spread of local
3 lower incidence of unilateral block
101
disadvantage dural puncture epidural technique
small chance of post dural puncture headache
102
epidural summary points
longer analgesia possible
more control of analgesic level
more gradual, less profound sympathectomy
less dense block
103
spinal summary points
limited analgesic duration
single shot (cant alter dose)
rapid potent sympathectomy
denser block
104
sacral hiatus
site of needle insertion
105
what is the sacral hiatus covered by?
sacrococcygeal ligament
106
sacral cornu
bony pominence to either side of sacral hiatus
| palpate these for landmarks
107
is a caudal block a spinal or epidural?
epidural block but differs because
performed at sacral level
dosed with single shot of drug
108
caudal block technique 5
1 palpate sacral hiatus
2 insert needle through sacral hiatus at 45 deg angle
3 advance sephalad until pop
4 advance cannula over the needle and remove needle
5 aspirate before inject
109
when is it possible for the epidural to cause spinal cord or nerve root damage?
in the lumbar or thoracic region
110
what will happen when epidural needles get too close to nerve roots?
patients experience parasthesias and the anesthetist can redirect
111
can lumbar and thoracic epidurals be done when the patient is asleep?
no they must be awake to reduce the risk of nerve injurt
112
can caudal blocks be done when the patient is asleep?
yes because they are so far away from the spinal cord or roots
113
what is the most popular block for children?
caudal block
114
3 advantages to caudal blocks
performed on asleep pts
more reliable perineal anesthesia (than lumbar)
less likely dural puncture and nerve damage
115
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
```
116
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
```
117
how does total mg dose affect spread?
higher doses spread more
118
how does volume injected affect spread
the higher volume will spread more
119
does dose or volume have greater affect on spread
dose
120
how does the addition of epi spread the block?
it prolongs the block but doesnt raise the level
121
how does addition of narcotic affect the block
increases the density "strength" of the block
122
how does the height of the patient affect the block
the shorter you are the more likely it will travel too high
123
how does trendelenburg effect block
more cephalad spread of local
124
how does reverse trendelenburg effect block
less cephalad spread of local
125
how does lateral effect block
block will be more one sided
126
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
127
why does local anesthetic spread higher in heavier patients?
increased intraabdominal pressure
compression of inferior vena cava
engorgement of epidural veins
decreases CSF volume
128
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)
129
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
```
130
what could infection at injection site or sepsis lead to
meningitis or epidural abscess
131
what must the platelet count be for OB before neuraxial blockade?
>80,000- 100,000
132
why should aortic/mitral stenosis be avoided with neuraxial blocks?
sympathectomy drops preload and afterload and those should be maintained with aortic stenosis
133
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
134
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)
135
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
```
136
what is the incidence of back pain following spinal anesthesia?
25%
137
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
```
138
what is a epidural abscess caused by
infection potentially after back surgery or neuraxial block
139
what are the symptoms of a epidural abscess
back pain intensified by spine percussion
signs of infection (fever, increases WBC)
sensory AND motor deficits
140
how is an epidural abscess diagnosed?
ct scan
141
treatment of epidural abscess
surgical decompression via laminectomy
142
how are the symptoms of epidural abscess and epidural hematoma different?
hematoma has faster onset and the WBC count should be normal
143
how are epidural hematomas treated
immediate surgical evacuation
144
what is transient neurologic symptoms?
someone who experiences back pain without motor deficits
| resolves on own
145
what are some hypothesis about what causes TNS
lithotomy position
intrathecal vasoconstrictors
highly concentrated local
lidocaine
146
which is more serious CES or TNS?
CES because it includes back pain and motor deficits and/or bladder and bowel dysfunction
147
etiology of CES
nerve root/spinal cord trauma
highly concentrated local anesthetics
continuous spinal anesthesia through microcatheter
148
which needs a neurology consult? CES or TNS
CES
149
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
150
if someone gets a wet tap what is the likelihood of PDPH
80% chance
151
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
152
if you are older are you more or less likely to get a PDPH?
less likely as you get older
153
symptoms of PDPH
headache bilateral frontal occipital and extends to neck
| aggravated by standing or sitting
154
why does standing make the headache worse
venous return decrease
epidural veins engorge
push out more CSF and worsen the headache
155
3 treatments for PDPH
autologous blood patch
analgesics, caffeine, generous fluid admin
neostigmine and atropine combination
156
what is the gold standard for PDPH treatment
blood patch, 90-99 success rate
157
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
158
how many "i" in esters
one
159
how many "i" in amides?
more than one "i"
160
how are esters metabolised
plasma esterases
161
what do esters produce as a byproduct and why does that matter
p-aminobenzoic acid PABA
| it is associated with allergic reactions
162
how are amides metabolized?
by the liver
163
which is more likely to cause an allergic reaction? tetracaine or marcaine?
tetracaine because it is an ester
164
what is the pH of local without epi
6-7
| acidic so it prolongs shelf life
165
what is the pH of local with epi
4-5
| more acidic because epi is unstable in basic environments
166
what local is most dramatically prolonged by the addition of adrenergic agonists
tetracaine (pontocaine)
167
how long does adding phenylephrine to tetracaine increase the duration of block
70-100%
168
how long does adding epi to tetracaine increase the duration of block
40-60%
169
how long does adding clonidine to tetracaine increase the duration of block
50-70%
170
what are the 4 most common local anesthetics for labor epidural dosing
marcaine
ropivacaine
lidocaine
chloroprocaine
171
marcaine advantages 2
motor sparing
| longest lasting
172
what is marcaine usually diluted to?
0.1-0.24%
173
marcaine disadvantages 3
1 less effective at blocking the larger sacral nerves
2 slowest onset
3 very cardiotoxic
174
what is the implication of marcaine being less effective at blocking larger sacral nerves
higher chance of losing their effectiveness during stage two labor
175
toxic dose marcaine with and without epi
2.5mg/kg w/o epi
| 3mg/kg w/ epi
176
what is the treatment for marcaine toxicity
CPR
| intralipid 20%
177
Ropivacaine (naropin) 0.2%
similar pharmacology to marcaine
| less cardiotoxic and more expensive
178
what is the max dose of ropivacaine
3mg/kg
179
advantages of lidocaine 2% or 1.5% with epi
more effective at blocking larger sacral nerves
| fast onset
180
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
181
what is the toxic dose of lidocaine with epi
7mg/kg
182
what is the toxic dose of lidocaine without epi
4mg/kg
183
chloroprocaine (3%) advantages
fastest epidural onset
| minimal drug transfer across placenta
184
when are you most often going to use chloroprocaine
emergency c section
185
why does chloroprocaine have such a rapid onset
pseudocholinesterase metabolism
186
chloroprocaine 3% disadvantages
```
highest degree of motor block
shortest duration (redosed frequently)
contraindicated for intrathecal use
```
187
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
```
188
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
189
signs of intravascular injection
increase HR
tinnitus
oral/tongue numbness
190
sings of intrathecal injection
immediate numbing of the legs
191
what is the initial test dose
5mL of 1.5% lido with 1:200,000 epi
192
accidental IV injection ruled out by absence of:
tachycardia
mouth/tongue numbness
ringing in ears
193
accidental intrathecal injection ruled out by
not having immediate numbness
194
epidural loading dose
additional 5mL loading dose after test dose to speed up the onset of block
higher risk of sympathectomy
195
why dose to increase the density of epidural block ?
patchy block when it starts to wear off, disconnect pump and bolus 5mL
196
when would you raise the epidural block gradually to t4?
non emergent c section
197
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
198
if local is bolused too fast what will happen
risk of high block and hypotension is increased
199
if the anesthetist waits too long in between boluses what happens?
the block density will increase but the block wont rise
200
what is the local of choice for raising an epidural block from t10 to t4?
lidocaine because fast onset and longer duration than chloroprocaine
201
what are common preservatives in local anesthetics?
sulfites (bisulfite, metabisulfite)
parabens (methylparaben)
EDTA
202
do multi dose or single dose vials have preservatives?
multidose vials
203
methylparaben
bacteriostatic preservative added to multidose vials
| potential anaphylactoid symptoms
204
what is methylparaben contraindicated for?
epidural and intrathecal
205
what are methylparaben free solutions referred to as?
MPF
206
sulfites (and citric acid) are added to what?
local that are premixed with epi to prevent degradation of epi
causes more pain on injection
207
what has intrathecal injection of sulfites resulted in?
arachadonitis
| anaphylactoid rxns
208
what are sulfites contraindicated for?
spinals
209
are sulfites okay to use for epidurals?
yes
210
what is EDTA used for?
prolong shelf life and allow autoclaving to sterilize glass vial
211
what is EDTA been linked to in patients?
epidurally injected associated with severe pain at injection site
212
can you use chloroprocaine for spinals?
no
213
what two things should you check before injecting epudural or intrathecal
preservative free
| "for spinal or epidural use"
214
can you use a local with preservatives for a bier block?
no
215
why is bicarb added?
added to lidocaine or chloroprocaine to speed up onset by bringing closer to pKa
216
how long until the local will precipitate when bicarb is added
6hr
217
effects of adding alpha agonist?
prolongs block duration
limits toxic side effects
enhances analgesic quality
218
what local is effected the most with added epi
tetracaine
219
what local is effected the least with added epi
bupivacaine
220
if the local is _____ lipid soluble then added epi is less significant.
more
221
can alpha agonists cause analgesia?
yes by directly inhibiting sensory and motor neurons
222
what does clonidine do to BP
greater decrease in BP
223
duramorph
morphine without preservatives
224
which causes more respiratory depression in fetus and urinary retention? morphine or fentanyl?
morphine
225
advantages of neuraxial opioids
analgesia
no motor blockade
no sympathectomy
226
disadvantages of neuraxial opioids
pruritus (itch)
delayed respiratory depression
nausea/vomiting
227
the more lipid soluble drugs they have a _____ onset and _____ duration
faster onset
| shorter duration
228
____ lipid soluble drugs exit the central nervous system quickly
more
229
duration of epidural narcotics
twice as long as spinal because epidural dose is higher
230
spinal dosing of opioids
should not be dosed if it is outpatient procedure
231
what are the three forms a drug can be in?
non polar
polar/neg charged (loss of H+)
polar/pos charged (gain of H+)
232
what is the form a drug takes determined by? 2
drugs pH
| pH of environment the drug is placed in
233
if you have higher degree of nonpolar drug then the onset is
faster
234
do the ionized or nonionized portion of the drug cross the lipid membrane?
nonpolar (nonionized)
235
if an acidic drug is placed in a basic environment then it will become:
negatively charged and slow the onset of the drug
236
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
237
what is the highest possible portion of nonpolar drug
50%
238
when you place a drug in an ideal pH then it will
have the highest portion of nonpolar drug and fastest onset possible
239
pKa
pH of the drugs environment that will result in the drug having 50% ionization and 50% nonionization
240
pH of lidocaine
6.5
241
pKa of lidocaine
7.9
242
what would you do to bring the pH of lidocaine closer to its pKa?
add sodium bicarb
243
do basic drugs have a high or low pKa
high
244
do acidic drugs have a high or low pKa
low
245
the drug will have a ____ onset the closer the drugs pKa is to physiologic pH 7.4
faster
246
are local anesthetics by themselves more acidic or basic?
basic
247
are local anesthetics in the vial more acidic or basic?
acidic
| acid added so it wont precipitate
248
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
249
how much lower is the pH of local when the solution contains epi?
1-1.5 units lower
250
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
251
effect of higher lipid solubility on local anesthetics onset and duration
slow onset
| long duration
252
effect of higher lipid solubility on other drugs such as fentanyl onset and duration
fast onset
| short duration
253
factors that determine local anesthetic potency 3
```
how concentrated (more=potent)
how lipid soluble (higher=potent)
total dose (more=potent)
```
