Neuraxial Anesthesia Flashcards
(252 cards)
1
Q
In adults, the spinal cord ends at
A
L1-L2
2
Q
In adults, the dural sac ends at
A
S2
3
Q
In kids, the spinal cord ends at
A
L2-L3
4
Q
In kids, the dural sac ends at
A
S3
5
Q
Neuraxial anatomy from layers of skin to CSF
A
- Skin
- Supraspinous ligament
- Interspinous ligament
- Ligamentum flavum
- Epidural space
- Dura mater
- Subarachnoid space (contains CSF)
6
Q
Where is the epidural space
A
Extends superiorly to the foramen magnum and inferiorly to the sacral hiatus
7
Q
Where is the spine normally convex anteriorly?
A
In the cervical and lumbar regions
8
Q
Posterior curvature of the spine
A
Kyphosis
9
Q
Anterior curvature of the spine
A
Lordosis
10
Q
Lateral curvature of the spine
A
Scoliosis
11
Q
Number of each vertebrae
A
7 cervical 12 thoracic 5 lumbar 5 sacral 4 coccygeal 33 total
12
Q
Number of spinal nerve roots
A
8 pair of cervical 12 pair of thoracic 5 pair of lumbar 5 pair of sacral 1 pair of coccygeal 31 total
13
Q
What does it mean if a small portion of nerve roots are covered by dural sheath?
A
- Roots close to the spinal cord tend to float in the dural sac and are thus usually pushed away, not pierced, by an advancing needle
- Nerve blocks close to intervertebral foramen carry a risk of subdural injection
14
Q
Most common starting insertion site for a spinal or lumbar epidural in adults
A
L3-L4
L4-L5 is also common and acceptable
15
Q
What may be considered if L3-5 attempts are unsuccessful for a spinal or lumbar epidural in adults?
A
L2-3
16
Q
Imaginary line drawn between superior aspects of the iliac crests
A
Tuffier’s line
17
Q
What does Tuffier’s line estimate?
A
L4 or L4-5 interspace
18
Q
How do you find the L3-4 space?
A
Palpate the superior aspects of the iliac crests and move up one interspace above Tuffier’s line
19
Q
What is a T10 level of analgesia for?
A
- Spontaneous vaginal delivery
- Inguinal surgery
- Testicular surgery
20
Q
What is a T4 level of analgesia for?
A
C-section
21
Q
The most dependent area of the spine when patients are supine
A
T4
22
Q
True/false. If the pt is placed supine immediately after the block is given, the normal dose will not go above T4-T6
A
True
23
Q
Why is it convenient that the spinal drug does not rise above T4-T6 if the patient is placed supine immediately after the block?
A
- It will usually go to the perfect height necessary for analgesia for a C-section
- It helps prevent the spread of local anesthetic above T4, which helps prevent high spinal or total spinal anesthesia
24
Q
When T5-L1 nerves are blocked with a spinal or epidural, causing vasodilation and subsequent hypotension
A
Sympathectomy
25
The earliest sign of more intense sympathectomy
Nausea/vomiting
26
When are sympathectomies usually more severe?
With spinal blocks
27
How do you treat nausea from sympathectomy?
Raise the pts blood pressure
28
Dermatomes where sympathectomy is common
T5-L1
29
Dermatome that contains accelerator fibers
T1-T4
30
What happens if the level of the neuraxial block starts to rise above T4?
The patient can have significant bradycardia
31
Dermatome with phrenic nerve innervation
C3-C5
32
What happens if the neuraxial block goes to C3-C5?
The patient will go apneic
33
How do you know if the block is getting to C6-C8?
The patient will experience tingling, numbness and/or weakness in their fingers
34
How do you decrease the level of the block below C6-C8?
Place them in reverse Trendelenburg
35
Carina dermatome
T4-T5
36
Xyphoid process dermatome
T6
37
Liver dermatome
T6-T11
38
Inferior border of scapulae dermatome
T7
39
Kidney dermatome
T8-L1
40
Orchiectomy dermatome
T10
41
Bladder dermatome
S2-S4
42
Blocking the nerves up to that level will have the potential to produce hypotension and bradycardia
Sympathetic (autonomic) blockade
43
Blocking nerves up to that level will produce an absence of pain
Sensory blockade
44
Blocking nerves up to that level will block the patient's ability to move those limbs
Motor blockade
45
Sympathetic blockade is typically 2 levels (higher/lower) than sensory blockade
Higher
46
Sensory blockade is typically 2 levels (higher/lower) than motor blockade
Higher
47
If a patient has a sensory block at T4, where would their motor and sympathetic block be?
Motor up to T6, sympathetic up to T2
48
When are nerves more easily blocked?
If they are smaller and myelinated
49
In spinal nerves, local anesthetic inhibition follows the sequence:
Autonomic > sensory > motor
50
What does the local anesthetic inhibition sequence mean?
1. It is easiest to block autonomic nerves
2. It is easier to block smaller pain nerves than it is to block larger motor nerves
3. It is possible for a patient to move even if they can't feel pain
4. It's not likely for a patient to have feeling if they can't move
51
Goal with an epidural
Stop the needle at the epidural space (do not puncture the dura)
52
Needle for epidural
Large 17ga Tuohy needle to allow for threading of catheter into epidural space
53
Epidural advantages (compared to spinals)
1. We can give analgesia as long as necessary
2. We have more control over the analgesic level
3. Patients experience a less profound sympathectomy
4. This is a better preservation of motor function
54
Epidural disadvantages compared to spinals
1. Not as dense as a spinal block
2. Very high probability for post dural puncture headache if the dura is accidentally punctured (larger the needle, the larger the hole in the dura, larger CSF leak, higher chance for PDPH)
3. Onset of action for local anesthetics is longer
4. More potential for local anesthetic toxicity
55
What is a "walking epidural"
Epidural dosed with either
1. Narcotics only, or
2. Lower doses/infusion rates of local anesthetic
that preserves motor function and allows patient to walk
56
Outline of spinal block
1. Dura punctured with spinal needle
2. Single "shot" of drug is given
3. Smaller needles are used (27ga, 25ga, 22ga)
57
Needle size for spinals
27ga, 25ga, 22ga
58
Spinal needle options
1. Whitacre
2. Sprotte
3. Quincke
59
Pencil point needle with smallest opening for spinals
Whitacre
60
Pencil point needle with longer opening for spinals
Sprotte
61
Cutting tip needle for spinals
Quincke
62
Spinal needle where CSF aspiration will be the hardest/slowest
Whitacre
63
Spinal needle where CSF can be easier to aspirate, but a higher chance of injecting epidurally
Sprotte
64
Spinal needle that cuts through ligaments better, but makes a larger hole in the dura
Quincke
65
Introducer needle size for spinals
18ga
66
Purpose of the 18ga introducer needle
Much less bending of the spinal needle, commonly used if the spinal needle is smaller than 22ga (25, 27ga)
67
Advantage of 22ga spinal needle
18ga introducer is not needed
68
Disadvantage of the 22ga spinal needle
There is a higher risk of spinal headache due to the larger hole in the dura
69
Common uses for the 22ga spinal needle
1. Elderly patients
| 2. Obese patients
70
Why is a 22ga common for elderly patients?
1. Geriatric patients carry a lower risk of spinal headache
| 2. Larger needles can pass through calcified ligament more easily
71
Why is a 22ga more common in obese patients
a larger needle is less likely to bend/break when passing through the excess tissue
72
Advantage to 25ga spinal needle
It's less likely for the patient to get a spinal headache
73
Most common size of spinal needle for adults
25ga
74
Disadvantage to 25ga spinal needles
More likely to bend when passing through spinal ligaments, especially if they are calcified, so it is commonly used with an 18ga introducer
75
Advantage to 27ga spinal needle
Creates the smallest hole in the dura, least chance of spinal headache
76
Disadvantage to 27ga spinal needle
Has the highest chance of bending through the spinal ligaments, so wouldn't want it by itself and wouldn't want to use an 18ga introducer because it doesn't pass through ALL spinal ligaments
77
When is a 27ga spinal needle commonly used?
When performing a combined spinal epidural block where is Tuohy needle is used as the introducer needle. The 27ga will only need to pass through ligamentum flavum
78
Rare technique that provides repeated doses of local anesthetic into the intrathecal space through a catheter
Continuous spinal anesthesia
79
What is needed to run a continuous spinal infusion?
Threading a microcatheter (24-32ga) into the subdural space
80
Problem with the microcatheters
Associated with neurotoxicity and cauda equina syndrome
81
What did the FDA advise against for continuous spinal anesthesia?
All small bore catheters (smaller than 24ga)
82
The only real practical use for continuous spinal anesthesia
If an anesthetist unintentionally punctures the dura with a Tuohy needle during epidural placement
83
Management of continuous spinal anesthesia
1. Sterile technique is critical
2. Catheter should be threaded 2-3 cm into the intrathetcal space
3. Analgesia is usually maintained with local anesthetic boluses instead of an infusion and titrated to effect
4. Appropriate dosing intervals are anywhere from 45-90 minutes
84
Dose of local anesthetic via continuous spinal infusion
Approximately 1/10th of epidural infusion rate and titrated to effect
85
Refers to whether the drug will sink or rise when injected into the CSF
Baricity
86
When the spinal drug is denser than CSF and the drug sinks
Hyperbaric
87
How are drugs made hyperbaric?
By adding an equal volume of 10% dextrose/glucose to the local anesthetic
88
Where do hyperbaric drugs tend to move?
T4
89
Peak concentration and duration of action of hyperbaric solutions
1. Shorter time to peak concentration
| 2. Shorter duration of action than plain local anesthetics
90
Performed by allowing the patient to remain sitting for several minutes after injecting hyperbaric spinal medication
Saddle block
91
What does the saddle block anesthetize?
Sacral nerves, buttocks, perineal area, inner thighs
92
When is a saddle block used?
For genitourinary procedures and to relieve 2nd stage labor pain
93
The spinal drug is ligher than CSF and the drug will rise
Hypobaric spinal
94
How do you make a drug hypobaric?
By adding sterile water
95
Most common use for hypobaric spinal
Hip surgery
96
Spinal drug has the same specific gravity as CSF, so it remains at the level of injection
Isobaric
97
How are drugs made isobaric?
By adding equal volume of CSF or normal saline to the local anesthetic
98
How long does it take for baricity of the spinal to settle?
10-15 minutes
99
Combined spinal epidural technique
1. Advance a CSE Tuohy needle into the epidural space
2. Thread a small 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 plcae
3. Thread an epidural catheter after the patient has been dosed with spinal drugs
4. Use the spinal for operative anesthesia and the epidural for postoperative anesthesia
100
Advantages to CSE
1. Denser block for a procedure than an epidural alone
2. Allows the spinal to be performed with a 27ga spinal needle, leading to the smallest chance of PDPH
3. Allows post op analgesia with an epidural in case the anesthetist does not want to use Duramorph in the spinal
101
CSE disadvantage
Cannot perform a test dose through the epidural catheter to make sure it is in the right place because the pt is already numb from the spinal block by the time the epidural is threaded
102
Dural puncture epidural technique
1. Place epidural needle
2. Insert spinal needle through Tuohy needles and puncture the dura
3. Remove spinal needle without dosing intrathecal medication
4. Place epidural catheter and hook up to infusion pump
5. Local anesthetic is primarily in epidural space, but the small puncture in intrathecal space allows some to leak in
103
Advantage of dural puncture epidural technique
1. Faster sacral onset
2. Greater sacral spread of the local anesthetic
3. Lower incidence of unilateral block
104
Disadvantage of dural puncture epidural
Small chance of post dural puncture headache (very small w/27ga needle)
105
Caudal anesthesia landmarks
Sacral hiatus: site of needle insertion, covered by sacrococcygeal ligament
Sacral cornu: Bony prominences to the sides of sacral hiatus
106
Palpated to find sacral hiatus
Sacral cornu
107
Performed by inserting a needle through the sacrococcygeal ligament into the sacral hiatus with medication injected into the epidural space
Caudal block
108
How does the caudal block differ from a regular lumbar epidural block?
1. Performed at the sacral level
| 2. Dosed with a single shot of drug (instead of catheter infusion)
109
Caudal technique
1. Palpate the sacral hiatus
2. Insert the needle through the sacral hiatus at a 45 degree angle
3. Advance cephalad until a "pop" is felt
4. Advance the cannula over the needle and remove the needle
5. Aspirate before injecting
110
Common caudal dose
1-1.25 mL/kg of 0.125% marcaine with epi
111
Why is it vital that patients remain awake during lumbar or thoracic epidurals?
They can alert the anesthetist to stop and redirect the needle if parasthesias are experienced
112
Why can caudal blocks be safely performed in asleep patients?
There is a lower chance of nerve damage and parasthesias because the needle is further from the spinal cord or any nerve roots
113
Most popular epidural block in children
Caudal block
114
Advantages of caudal anesthesia
1. They can be performed in asleep patients
2. They provide more reliable perineal anesthesia than lumbar epidurals
3. Less likely chance of dural puncture and nerve damage
115
Disadvantages of caudal anesthesia
1. Dura can still theoretically be punctured
2. The rectum can be punctured
3. More difficult in adults
4. Requires 2x as much local as a lumbar epidural
5. Relatively high risk of urinary retention
116
Factors that affect the strength and spread of the neuraxial local anesthetics (8)
1. Total volume injected (10 mL 1% lido will spread more than 1mL 10% lido)
2. Total mg dose (higher doses spread faster)
3. Addition of epi
4. Addition of narcotic
5. Height of the patient (more than weight)
6. Positioning
7. Weight of patient
8. Age
117
True/false. Dose has a greater effect than volume in neuraxial local anesthetics
True
118
True/false. Epi prolongs the block and raises the block level
False. Epi prolongs the block but does NOT raise the block level
119
Effect of narcotic on neuraxial block
Increases the density/strength
120
Effect of height on neuraxial block
The shorter you are, the more likely the block will travel "too high"
Shorter people receive a lower dose
121
Effect of trendelenburg on neuraxial blocks
More cephalad spread of local anesthetic
122
Effect of reverse trendelenburg on neuraxial blocks
Less cephalad spread of local anesthetic
123
Effect of lateral positioning on neuraxial blocks
Block will be more one sided
124
Effects of neuraxial blocks on obese patients
- The higher the local will spread
| - Lower local dose requirement
125
Effects of age on neuraxial local anesthetics
1. Lower dosing requirement for geriatric patients
2. Shorter onset of epidural and spinal anesthesia in geriatric patients
(no evidence for differences in duration in elderly)
126
Absolute contraindications to neuraxial anesthesia
1. Patient refusal
2. Infection at the injection site
3. Severe hypovolemia
4. Coagulopathy
5. Severe aortic stenosis
6. Severe mitral stenosis
7. Sepsis
8. Elevated intracranial pressure
127
Why is infection at the injection site an absolute contraindication to neuraxial anesthesia?
A block could lead to possible meningitis or an epidural abscess
128
Why is severe hypovolemia an absolute contraindication to neuraxial anesthesia
There is a good chance the patient would not be able to tolerate the sympathectomy
129
Why is coagulopathy an absolute contraindication for neuraxial anesthesia?
It could lead to possible epidural hematoma, which includes thrombocytopenia, or elevated PTT or PT/INR
130
In OB, platelet counts > ____ are generally considered safe prior to neuraxial blockade
80,000-100,000
131
Why are severe aortic stenosis and mitral stenosis absolute contraindications to neuraxial anesthesia?
Sympathectomy drops preload and afterload, and preload/afterload need to be maintained with stenosis
132
Why is sepsis an absolute contraindication in neuraxial blocks?
Block placement can lead to possible meningitis and/or epidural abscess
133
Why is elevated ICP an absolute contraindication to neuraxial blocks?
Pts with ICP cannot tolerate the sympathectomy because a high MAP is required to perfuse the head in patients with intracranial hypertension
134
Relative contraindications to neuraxial anesthesia (4)
1. Neurologic deficiencies
2. Sepsis
3. Previous back surgery
4. Severe COPD
135
Complications from neuraxial blocks (11)
1. Pruritus
2. Nausea & vomiting (from hypotension)
3. Urinary retention
4. Parasthesias
5. Nerve/ spinal cord injury
6. Backache
7. PDPH
8. Transient neurologic symptoms
9. Cauda equina syndrome
10. Epidural abscess
11. Epidural hematoma
136
Incidence of back pain following spinal anesthesia
25%
137
Possible etiologies of back pain after spinal anesthesia
1. Common backache from needle or lying flat
2. Epidural abscess
3. Epidural/spinal hematoma
4. Transient neurologic symptoms
5. Cauda equina syndrome
138
Symptoms of epidural abscess
Takes days or weeks to develop
1. Back pain intensified by spine percussion
2. Signs of infection
3. Sensory and motor deficits
139
Diagnosis of epidural abscess
CT scan
140
Treatment of epidural abscess
Surgical decompression via laminectomy
141
Difference between epidural hematoma and epidural abscess
1. Faster onset of hematoma
2. White count is normal
3. Hematoma requires immediate surgical evacuation
142
Back pain without motor deficits
Transient neurologic symptoms (TNS)
143
Treatment of TNS
Resolves on its own
144
Cauda equina syndrome
back pain and motor deficits (paresis of the legs, bladder and bowel dysfunction)
145
Etiology of TNS
Unclear, possibly lithotomy position, intrathecal vasoconstrictors, highly concentrated local anesthetics, spinal lidocaine
146
Etiology of cauda equina syndrome
Nerve root and/or spinal cord trauma, highly concentrated spinal local anesthetics, and continuous spinal anesthesia through a microcatheter
147
Patients who get a wet tap are up to 80% likely to get ____
a PDPH
148
Protocol for PDPH
1. Thread a catheter ~2cm intrathecally for continuous spinal anesthesia
2. Remove the needle and start another epidural at higher dermatome level
149
Symptoms of PDPH
1. Headache pain that is bilateral, frontal, occipital, and extends into the neck
2. Pain is aggravated by sitting or standing, and may last for weeks
150
Incidence of post dural puncture headache decreases with ___
age
151
Why is PDPH exacerbated by sitting and standing?
Venous return decreases in those positions, and decreased venous return engorges the epidural veins and drives more CSF out
152
Treatment for PDPH
1. Autologous blood patch (GOLD STANDARD)
2. Analgesics, caffeine, steroids and generous fluid administration
3. Neostigmine (0.02 mg/kg) and atropine (0.01mg/kg) combination
153
When should blood patches be done for PDPH?
After all signs that the local anesthetic has worn off
154
When is the neostigmine/atropine combo effective for PDPH?
After only 2 doses
155
Advantages of regional anesthesia compared to GA
1. Decreased anesthetic requirements (dec postop N/V)
2. Decreased respiratory complications
3. Decreased surgical blood loss
4. Decreased incidence of thrombosis (due to dec platelet aggregation)
156
Ester local anesthetics
1. Tetracaine
2. Chloroprocaine
3. Cocaine
4. Novocaine
157
Ester metabolism
By plasma esterases and produce p-aminobenzoic acid (PABA) as byproduct
158
Which local anesthetic is more likely to cause allergic reactions?
Esters due to PABA
159
Amide local anesthetics
1. Bupivicaine
2. Ropivacaine
3. Lidocaine
160
Amide metabolism
Liver
161
Why are local anesthetics without epi slightly acidic? (pH 6-7)
Acidity prolongs shelf life of the local anesthetic
162
Why are local anesthetics with epi more acidic (pH 4-5)?
Epi is unstable in basic environments
163
Longest acting spinal local anesthetic
Tetracaine (pontocaine)
164
Epinephrine may prolong tetracaine spinal anesthesia by ___
40-60%
165
Clonidine prolongs tetracaine spinal block by ___
50-70%
166
Most common local anesthetic we use for spinal anesthesia
Spinal marcaine (0.75%)
167
Duration of spinal marcaine
2 hours
168
Local that's ability for duration to be prolonged is LEAST affected by epinephrine
Marcaine
169
Should only be considered if the procedure were very short and the anesthetist wanted the spinal to wear off as fast as possible
Spinal lidocaine (5%)
170
Why is spinal lidocaine not commonly used for spinal anesthesia?
Intrathecal use has been associated with transient neurologic symptoms and cauda equina syndrome
171
Contraindicated drug for intrathecal use
Chloroprocaine
172
Most common local anesthetics for labor epidural dosing
1. Marcaine
2. Ropivacaine
3. Lidocaine
4. Chloroprocaine
173
Advantages of epidural marcaine
1. Motor sparing (does not block motor nerves as well)
| 2. Longest lasting
174
Most common local anesthetic for labor epidurals
Marcaine
175
Disadvantages of epidural marcaine
1. Less effective at blocking the larger sacral nerves
2. Slowest onset of all commonly used local anesthetics
3. Very cardiotoxic
176
Why do marcaine epidurals have a higher chance of losing their effectiveness during stage II labor?
The fetal head is pressing on the pelvis/sacral nerves during stage II labor
177
Toxic dose of marcaine
2.5 mg/kg w/o epi
| 3mg/kg w/epi
178
Bupivacaine toxicity treatment
1. CPR
| 2. Intralipid 20%
179
Implications of epidural ropivacaine
1. Similar pharmacology to marcaine with similar results
2. Less cardiotoxic, but more expensive than marcaine
3. Max recommended dose of ropivacaine is 3mg/kg
180
Advantages of epidural lidocaine
1. More effective at blocking the larger sacral nerves
| 2. relatively fast onset
181
Disadvantages of epidural lidocaine
1. More significant motor blockade than marcaine
| 2. Toxic dose causes neurologic symptoms (confusion, tinnitus, oral numbness, seizures)
182
Epidural drug more likely to inhibit parturient from pushing effectively during delivery
Lidocaine due to motor blockade
183
Toxic dose of epidural lidocaine
4mg/kg w/o epi
| 7mg/kg w/epi
184
Advantages of epidural chloroprocaine
1. Fastest epidural onset
| 2. Minimal drug transfer across the placenta
185
What causes rapid onset of epidural chloroprocaine?
Psuedocholinesterase metabolism
186
Perfect choice for bolusing an epidural for emergency C-section
Chloroprocaine
187
Disadvantage of epidural chloroprocaine
1. Produces the highest degree of motor block
| 2. Has the shortest duration
188
When are epidurals bolused instead of infused?
1. Initial test dose
2. Loading dose
3. Dose to increase block intensity
4. Raising block to T4 gradually
5. Raising block to T4 level immediately
189
What should you do prior to bolusing an epidural?
1. Verify the patient is stable
| 2. Aspirate to rule out intravascular or intrathecal injection
190
Signs of intravascular injection
1. Fast heart rate
2. Tinnitus
3. Oral/tongue numbness
191
Signs of intrathecal injection
Immediate numbing of the legs
192
Why should a patient be monitored for 10 minutes after every epidural bolus?
To ensure stable BP because the pt can have sympathectomy and subsequent hypotension
193
What is an initial epidural test dose?
5mL dose of 1.5% lidocaine with 1:200,000 epi right after the epidural is placed
194
How is accidental IV injection ruled out with the epidural test dose?
In the absence of:
1. Tachycardia (from the epi)
2. Mouth/tongue numbness, or a metallic taste in the mouth (from the lido)
3. Ringing in the ears
195
How do you rule out accidental intrathecal injection from an epidural test dose?
If there is no gradual onset of numbness
196
What is the epidural loading dose?
5 mL of marcaine or ropivacaine right after the initial 5mL test dose is given
197
Advantage of the epidural loading dose
It speeds up the onset of the block
198
Disadvantage of the loading dose
It can raise the level of the block above T10 and make a sympathectomy much more likely
199
What can you do if there is a patchy block?
Dose ~5mL of local (2% lidocaine)
200
When would you need to gradually raise the level of the epidural block to T4?
For a non-emergent C-section
201
How do you gradually raise the epidural block?
1. Give an initial 10 mL of local anesthestic, wait 3 min, check the dermatome level
2. Give an additional 5mL of local
3. Give a final 5 mL of local (for total of 20 mL) if block is not high enough
202
When is the risk of high block and hypotension increased?
If the local anesthetic is bolused too fast
203
What happens if you wait too long in between epidural boluses?
The block density will increase, but the block will not rise
204
When raising an epidural block from T10 to T4, the local anesthetic of choice is probably
Lidocaine
205
How do you raise the epidural block level immediately?
Bolus 20 mL of epidural anesthetic all at once
206
Best choice of local anesthetic for emergency C-sections
20 mL of 3% chloroprocaine (600mg)
207
Common preservatives in local anesthetics
1. Sulfites
2. Parabens
3. EDTA
208
True/false. A single dose vial contains preservatives
False
209
Bacteriostatic preservative in multidose vials of local anesthetics that can cause anaphylactoid symptoms
Methylparaben
210
Preservatives contraindicated for both epidural and intrathecal administration
Methylparaben
211
Preservative used for epidural use, but not spinal use
Sulfite
212
Purpose of sulfites
To prevent degradation of epinephrine in an alkaline pH
213
Preservative used to prolong shelf life and enable manufacturer to autoclave to sterilize the vial
EDTA
214
Large volumes of epidurally injected local anesthestic with EDTA has been associated with
Severe pain at the injection site
215
Even though chloroprocaine is now EDTA free, it is still contraindicated for
Spinal use
216
Preservatives associated with neurotoxicity
Sulfites and parabens
217
Added to lidocaine or chloroprocaine to speed up the onset when bolusing
Bicarb
218
When would you most want to bring the drug closer to its pKa when bolusing?
When raising the block level from T10 to T4
219
Disadvantage to bicarb
Causes the local anesthetic to precipitate within 6 hours
220
Purpose of alpha agonists with neuraxial anesthesia
1. Prolongs block duration
2. Limits toxic side effects
3. Enhances analgesic quality
221
Why does epinephrine have the least effect on the duration of bupivacaine?
It is highly lipid soluble
222
What is significant about epinephrine with tetracaine
Tetracaine is highly lipid soluble (higher than bupivacaine) but epi has the greatest effect on the duration
223
Associated with greater decrease in BP and can prolong block duration when administered orally
Clonidine
224
Morphine without preservatives
Duramorph
225
Carries a higher risk of urinary retention when compared to fentanyl
Morphine
226
Causes more respiratory depression in fetus than fentanyl
Morphine
227
Advantages of neuraxial opioids
1. Analgesia
2. No motor blockade
3. No sympathectomy
228
Disadvantages of neuraxial opioids
1. Pruritus
2. Delayed respiratory depression
3. Nausea/vomiting
229
Most common complication of neuraxial narcotics
Pruritus
230
When is delayed respiratory depression more likely to occur with neuraxial opioids?
Following intrathecal morphine than intrathecal fentanyl because morphine is less lipid soluble than fentanyl
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What is significant about spinal dosing of opioids?
Narcotics should NOT be added to the spinal if the procedure is outpatient due to risk of respiratory depression
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Significance of intrathecal dexmedetomidine
Similar analgesia and less pruritus and shivering compared with morphine
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What determines the form the drug takes on?
1. pH of the environment the drug is placed in
| 2. The drug's pKa
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The more polar/charged the drug is, the (slower/faster) the onset
The slower the onset
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The more nonpolar/non-ionized a drug is, the (slower/faster) the onset
Faster
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If we can get a drug to be 50% ionized, it will have the (slowest/fastest) onset possible
Fastest
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If an acidic drug is placed in a basic environment, it will become (positively, negatively, neutrally) charged
Negatively
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If a basic drug is placed in an acidic environment, it will become (positively, negatively, neutrally) charged
Positively
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What is ideal pH for a drug?
The pH of the drug's environment that will result in 50% ionizations and 50% nonionization which leads to the highest nonpolar portion possible (pKa)
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Acidic drugs have a (high/low) pKa
Low
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Basic drugs have a (high/low) pKa
High
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It takes a basic environment to prevent a (acidic/basic) drug from becoming positively charged
Basic
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Local anesthetic drugs are (acidic/basic)
Basic
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Local anesthetic solutions are (acidic/basic)
Acidic
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Why is adding acid to local anesthetics good and bad?
Good: prolongs shelf life
Bad: Slows down onset by leading to higher portion of ionized/positively charged drugs
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How can you speed up the onset of local anesthetics?
Add bicarb
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The pH of a drug solution is 4.5. The pKa of a drug is 10.7. Adjusting the pH of the drug to ___ will result in the fastest onset
10.7
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True/false. 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 drug onset
False
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Factors that determine local anesthetic onset
1. How ionized the anesthetic is
2. How close the local anesthetic's pH is to the pKa (the closer, the faster)
3. How close the local's pKa is to physiologic pH (the closer, the faster)
4. How lipid soluble the local is
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Higher lipid solubility for local anesthetics = (slower/faster) onset and (shorter/longer) duration
Slower onset, longer duration
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Higher lipid solubility for other drugs = (slower/faster) onset and (shorter/longer) duration
Faster onset and shorter duration
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Factors that determine local anesthetic potency
1. How concentrated the local anesthetic is (more concentrated = more potent)
2. How lipid soluble the local is (more potent = more lipid soluble)
3. The total dose (higher dose = more potent)
