Download OB Regional Anesthesia Review

OB Regional Anesthesia Review
Baricity:
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equal to the density of the local anesthetic divided by the density of the CSF
main determinant of how the local anesthetic is distributed when injected into the CSF
Local anesthetics can be…..when compared to CSF:
o Hypobaric: Baricity<1.0, Med in H2O, ↓ density than CSF → rise; positioning of pt after
injection is important (for perineal/anal sx, in prone/jackknife)
o Isobaric: Baricity = O, remains in the level of the injection; positioning does not affect spread
of LA
o Hyperbaric: Baricity > 1, med in dextrose, ↑ density than CSF → “fall”, positioning is
important
Density, Specific Gravity, and Baricity of Different Substances and Local Anesthetics
Density
Specific Gravity
Water
0.9933
1.0000
CSF
1.0003
1.0069
Hypobaric
Tetracaine
0.33% in water
0.9980
1.0046
Lidocaine
0.5% in water
N/A
1.0038
Isobaric
Tetracaine
0.5% in 50% CSF
0.9998
1.0064
Lidocaine
2% in water
1.0003
1.0066
Bupivacaine
0.5% in water
0.9993
1.0059
Hyperbaric
Tetracaine
0.5% in 5% dextrose
1.0136
1.0203
Lidocaine
5% in 7.5% dextrose
1.0265
1.0333
Bupivacaine
0.5% in 8% dextrose
1.0210
1.0278
Bupivacaine
0.75% in 8% dextrose
1.0247
1.0300
Levels for major procedures:
Body Landmark
Dermatome Level
Little finger
C8 (All cardio
accelerator fibers
blocked)
Nipples
T4
Xiphoid
T6
Inferior edge of
Scapula
Umbilicus
Baricity
0.9930
1.0000
0.9977
0.9985
0.9995
1.0003
0.9990
1.0133
1.0265
1.0207
1.0227
Procedure
Upper abdominal surgery
Intestinal, gynecologic, and urologic
surgery
T7
T10
Vaginal delivery of a fetus, and hip surgery
L1
Thigh surgery and lower leg amputations
L2
Foot and ankle surgery
Spinal cord ends at L1-2, place spinals below this level.
Superior iliac crest
L4
Inferior iliac crest
S2
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S2 to S5 (saddle
block)
Perineal and anal surgery
Spinal
Smaller doses of LA (mg) → mg block →
→Lower potential for toxicity
Faster onset
Limited Duration
Lower failure rate (CSF is definitive for location)
Baricity has an effect
Epidural
Larger doses of LA (ml) → Volume block →
→Higher potential for toxicity
Slower onset
Flexible duration
Higher failure rate
Baricity has no effect (no CSF to create Baricity)
Doses for Spinal Blocks:
Dose, Duration, and Onset of Local Anesthetics Used in Spinal Anesthesia
Dose (mg)
Duration (min)
With 0.2mg
Plain
Epinephrine
to T10 to T4
Commonly Used
Lidocaine 5%
Bupivacaine 0.75%
50–75
8–12
Onset (min)
75–100
14–20
60–70
90–110
75–100
100–150
3–5
5–8
12–16
60–80
18–20
N/A
45
70–90
140–160
140–200
135–170
80–120
120–180
N/A
N/A
N/A
130–170
3–5
2–4
3–5
4–8
2–4
Less Commonly Used
Tetracaine 0.5%
Mepivacaine 2%
Ropivacaine 0.75%
Levobupivacaine 0.5%
Chloroprocaine 3%
6–10
N/A
15–17
10–15
30
Drug
Onset
Maximum Dose
Duration
(with epinephrine); (with Epinephrine)
Max mg dose
Lidocaine
Rapid
4.5 mg/kg (7 mg/kg) 120 min (240 min)
300mg (500 mg)
Bupivacaine
Slow
2.5 mg/kg (3 mg/kg) 4 hours (8 h)
175mg (225mg)
Chloroprocaine Rapid
(short
duration)
10 mg/kg (15
mg/kg)
800mg (1000mg)
30 min (90 min)
Doses for spinal blocks depend on:
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Height of pt → determines the volume of the subarachnoid space
Segmental level of anesthesia desired
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
Duration of anesthesia desired
Doses for Epidural blocks (Volume blocks): the volume depends on the location the catheter tip in the
epidural space as the size of the segmental epidural spaces increases down the spinal cord as the spinal cord
occupied less and less space.
Site of procedure
Dose in ml
T12-L2
8-12ml
Chest
L2
12-16ml
Upper Abdomen
(Cholecyctectomy, gastric
resection)
Lower Abdomen
Colon resection, aortic aneurysm, L2
12-16ml
retro pubic prostatectomy
Herniorrhaphy
L3
8-12ml
hysterectomy
L3
10-14ml
Lower Extremities
Anesthesia
L4
10-14ml
Sympathetic block
L2
8-12ml
Perineum (TURP, vaginal
L4
8-12ml
hysterectomy)
Back and flank (nephrectomy)
L2
10-14ml
Vaginal delivery
1st stage labor
L3
5-7ml
nd
rd
2 and 3 stage labor
L3
10-12ml
Nagelhout p. 1067
Opioids in Regional Anesthesia:
Epidural anesthesia:
Hydrophilic opioids (Morphine) spread easily within CSF and can enhance surgical anesthesia and
provide postoperative pain control.
Lipophilic opioids (Fentanyl) rapidly absorbed into systemic circulation → no strong effect.
Epidural Opioids Bolus Dose
Onset
Peak
Duration
Morphine
2-5mg
20-30min
30-60min
12-24hr
Hydromorphone
1 mg
10-15min
20-30min
8-15hrs
Nagelhout p.1069
Spinal anesthesia: Spinal doses are approximately 10 times less than the epidural doses.
Morphine: 0.1-0.5mg can provide pain control for ~24hrs, but necessitates in-hospital monitoring for
respiratory depression → is the traditional opioid for prolonged pain management.
Fentanyl: 25mcg for short surgical procedures, pts can be discharged home the same day.
Transient neurological symptoms (TNS) syndrome of pain and dysesthesias that may occur in up to 1/3 of
pts receiving intrathecal doses of lidocaine.
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Pathogenesis of TNS is believed to represent concentration dependent neurotoxicity of local anesthetics
Rarely occurs with other local anesthetics
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Mechanism responsible is unknown
Increased incidence in pts in lithotomy position, positioning for knee arthroscopy, and outpatient
procedures
Symptomstypically include back pain, weakness, and numbness radiating to one or both buttocks and
down the legs, or both. Does not consistently manifest with sensory/motor deficits or reflex
abnormalities.
o Appear within first 12-24 hours after surgery
o Exclusively a pain syndrome, no bowel or bladder dysfunction
o All neuro, MRI and Electrophysiologic examinations are normal
o Most often resolve within 3 days, rarely last a week.
Pain is often more severe than the surgical procedure.
TreatmentNSAIDs, possibly opioids if severe pain, and trigger point injections, time to allow
symptoms to pass
Caudal equina syndromeresult of an injury below the level of the conus, or caudal end of the cord, typically
below L2. Persistent paresthesia and limited motor weakness are the most common injuries
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Nerve roots within the subarachnoid space are highly vulnerable to chemical damage, particularly the
sacral roots which are poorly myelinated.
 Typically results from compression within the lumbar spinal canal or from chemical damage
Risk factors

Poor subarachnoid dispersion of LA
o Block failure, followed by a repeat injection
o Fine-gauge or pencil point needle
o Spinal micro catheter
o Continuous infusion
o Hyperbaric anesthetic solution
o Lithotomy position
 Unintentional intrathecal injection of a large volume intended for the epidural space
 Incorrect formulation, with unsuitable preservative or antioxidant
 Intrathecal LIDOCAINE, particularly 5%
 Can be caused by an epidural hematoma
Treatmentsteroids, anti-inflammatory medications, decompression if related to hematoma
Epidural hematomadamage to vessel or anticoagulation can cause a hematoma to form in epidural space.
Incidence <1 in 150,000
Symptoms includecan initially be hard to see in pts with an epidural or spinal block
 Severe, localized back pain with delayed radicular radiation that may mimic disk herniation
 Weakness
 Numbness
 Urinary incontinence
 Fecal incontinence
Risk factors

Difficult or traumatic epidural needle/catheter placement or spinal placement
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 Coagulopathy or therapeutic anticoagulation
 Spinal deformity
 Spinal tumor
Early recognition is critical as delay of more than 8 hours in decompressing the spine reduces the odds of good
recovery. Treatment is surgical removal of the pressure on the spine.
Important to review what meds the pt is onepidural/spinals should not be done on pts taking antiplatelet drugs
unless they have been held for a specific time frame. Also pts on LMWH at high risk. Timing of catheter
removal is crucial as removal can cause hematoma formation as well.
Blood patchregarded by many as the gold standard treatment for PDPH. Blood is drawn using sterile
technique. All air is removed from the syringe. It is then injected into the epidural space near the area of the
where the dura was inadvertently punctured.
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Idea is that the blood will help “patch” the hole in the dural space preventing continued leak of CSF
Possibly blood in epidural space helps more to tamponade the leak of CSF vs actually seal the puncture.
Exact volume used is debatable, average 12-15 mL is used, but can inject up to 20 mL. With larger
volume. The injection is terminated when volume is instilled or pt complains of severe back, leg, or neck
pain or pressure.
Headache is often relieved immediately
After procedure pt should lie flat and rest for 1-2 hours. Pt may resume ambulation after 2 hours but
should avoid vigorous physical activity, heavy lifting, or any activity involving a valsalva maneuver.
Procedure may be repeated if first fails. Often second procedure provides relief. If second fails to relieve
PDPH, get neuro consult.
Two main complications
o Infection
o Neurologiclow back pain with neuro impairment of the lower extremities, subdural hematoma,
arachnoiditis, radicular back pain, pneumocephalus, seizures, and acute meningeal irritation.
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Spinal
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Anatomy
o Midline approach
 Skin
 Subcutaneous fat
 Supraspinous ligament
 Interspinous ligament
 Ligamentum flavum
 Dura mater
 Subdural space
 Arachnoid mater
 Subarachnoid space
o Paramedian approach
 Skin
 Subcutaneous fat
 Ligamentum flavum
 Dura mater
 Subdural space
 Arachnoid mater
 Subarachnoid space
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
Dermatome
o The fourth thoracic (T4)
corresponds to the nipples.
o The sixth thoracic (T6)
corresponds to the xiphoid.
o The tenth thoracic (T10)
corresponds to the umbilicus.
dermatome
dermatome
dermatome
Table 1. Dermatomal Levels of Spinal Anesthesia for Common Surgical Procedures
Procedure
Dermatomal Level
Upper abdominal surgery
T4
Intestinal, gynecologic, and urologic surgery
T6
Transurethral resection of the prostate
Vaginal delivery of a fetus, and hip surgery
T10
Thigh surgery and lower leg amputations
L1
Foot and ankle surgery
L2
Perineal and anal surgery
S2 to S5 (saddle block)
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 Medications
Table 4. Dose, Duration, and Onset of Local Anesthetics Used in Spinal Anesthesia
Duration
(min)
Dose (mg)
With 0.2 mg
Epinephrine
Onset
(min)
60–70
75–100
3–5
14–20
90–110
100–150
5–8
6–10
12–16
70–90
120–180
3–5
N/A
60–80
140–160
N/A
2–4
Ropivacaine 0.75%
15–17
18–20
140–200
N/A
3–5
Levobupivacaine 0.5%
10–15
N/A
135–170
N/A
4–8
30
45
80–120
130–170
2–4
to T10
to T4
Plain
50–75
75–100
8–12
Tetracaine 0.5%
Mepivacaine 2%
Commonly Used
Lidocaine 5%
Bupivacaine 0.75%
Less Commonly Used
Chloroprocaine 3%
o Additives
 Vasoconstrictors – epinephrine and phenylephrine – limit systemic reabsorption and
prolong duration of action by keeping the local anesthetic in contact with the nerve fibers
 Alpha-2-adrenergic agonists enhance pain relief and prolong sensory block and motor
block
 i.e. clonidine
 Acetylcholinesterase inhibitors prevent the breakdown of acetylcholine and produce
analgesia when injected intrathecally
 i.e. neostigmine
o Factors determining spinal level blockade and spread
 Baricity of the local anesthetic solution
 Position of the patient during and just after injection
 Dose of the anesthetic injected
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Table 2. Determinants of Local Anesthetic Spread in the Subarachnoid Space
Properties of local anesthetic solution
Baricity
Dose
Volume
Specific gravity
Patient characteristics
Position during and after injection
Height (extremely short or tall)
Spinal column anatomy
Decreased CSF volume (increased Intraabdominal pressure due to increased
weight, pregnancy, etc.)
Technique
Site of injection
Needle bevel direction

Risks/side effects
o Contraindications
 Absolute
 Patient refusal
 Sepsis at the site of injection
 Hypovolemia
 Coagulopathy
 Indeterminate neurological disease
 Increased intracranial pressure
 Relative
 Infection distinct from the site of injection
 Unknown duration of surgery
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o Complications
 Permanent neurologic injury - can occur after needle introduction into the spinal cord or
nerves, spinal cord ischemia, bacterial contamination of the subarachnoid space, or
hematoma formation
 After low-molecular-weight heparin (LMWH) administration, delay spinal
anesthesia for 10 to 12 hours
 If blood is noted during needle placement, delay LMWH therapy for 24 hours
 In cases of continuous spin anesthesia and accidental LMWH therapy, remove the
catheter 10-12 hours after the last dose of LMWH
 Avoid spinal anesthesia for 14 days after the last dose of ticlopidine (Ticlid) and 7
days after clopidogrel (Plavix)
 Patients should not receive glycoprotein IIb/IIIa inhibitors for 4 weeks after
surgery, and do not attempt spinal anesthesia until platelet function returns to
normal
 Caudal equina syndrome – associated with the use of continuous spinal micro catheters.
Use of hyperbaric 5% lidocaine for spinal anesthesia is also associated with an increased
incidence of cauda equina syndrome
 Arachnoiditis – known to occur after intrathecal steroid injection. Causes include
infection, myelograms from oil-based dyes, blood in the intrathecal space, neuroirritant,
neurotoxic/neurolytic substances, surgical interventions in the spine, intrathecal
corticosteroids, and trauma
 Meningitis – bacterial or aseptic
 Post dural puncture headache – result of loss of CSF with incidence up to 25% after
spinal anesthesia. Headache is characteristically worse when the head is elevated and
becomes milder or completely relieved when the patient is supine.
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
High spinal – can result in profound respiratory impairment, most likely due to brainstem
ischemia. If the blood pressure and cardiac out become too low due to vasodilation,
cerebral blood flow can be impaired
Cardiovascular collapse – rare event. Bradycardia usually precedes cardiac arrest, and
early aggressive treatment of bradycardia is warranted. Treatment with atropine,
ephedrine, and epinephrine with ACLS protocol initiated
Page 10 of 17
Epidural Block
Patient Selection
-cooperative
-can also be used in the cervical and thoracic areas as well—levels at which spinal anesthesia is not advised.
-a continuous technique has been found to be helpful in providing epidural local anesthesia or opioid analgesia
after major surgical procedures.
Pharmacologic Choice
Chloroprocaine, an amino ester local anesthetic, is a short-acting agent that allows efficient matching of the
length of the surgical procedure and the duration of epidural analgesia, even in outpatients. 2-Chloroprocaine is
available in 2% and 3% concentrations; the latter is preferable for surgical anesthesia and the former for
techniques not requiring muscle relaxation.
Lidocaine is the prototypical amino amide local anesthetic and is used in 1.5% and 2% concentrations
epidurally. Concentrations of mepivacaine necessary for epidural anesthesia are similar to those of lidocaine;
however, mepivacaine lasts from 15 to 30 minutes longer at equivalent dosages. Epinephrine significantly
prolongs (i.e., by approximately 50%) the duration of surgical anesthesia with 2-chloroprocaine and either
lidocaine and mepivacaine. Plain lidocaine produces surgical anesthesia that lasts from 60 to 100 minutes.
Bupivacaine, an amino amide, is a widely used long-acting local anesthetic for epidural anesthesia. It is used in
0.5% and 0.75% concentrations, but analgesic techniques can be performed with concentrations ranging from
0.125% to 0.25%. Its duration of action is not prolonged as consistently by the addition of epinephrine, although
up to 240 minutes of surgical anesthesia can be obtained when epinephrine is added.
Ropivacaine, another long-acting amino amide, is also used for regional and epidural anesthesia. For surgical
anesthesia it is used in 0.5%, 0.75%, and 1% concentrations. Analgesia can be obtained with concentrations of
0.2%. Its duration of action is slightly less than that of bupivacaine in the epidural technique, and it appears to
produce slightly less motor blockade than a comparable concentration of bupivacaine.
In addition to the use of epinephrine as an epidural additive, some anesthesiologists recommend modifying
epidural local anesthetic solutions to increase both the speed of onset and the quality of the block produced. One
recommendation is to alkalinize the local anesthetic solution by adding bicarbonate to it to achieve both these
purposes. Nevertheless, the clinical advisability of routinely adding bicarbonate to local anesthetic solutions
should be determined by local practice protocols.
Placement
Anatomy
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When a lumbar approach to the epidural space is used in adults, the depth from the skin to the
ligamentum flavum is commonly near 4 cm; in 80% of patients the epidural space is cannulated at a
distance of 3.5 to 6 cm from the skin. In a small number of patients the lumbar epidural space is as near
as 2 cm from the skin.
In the lumbar region, the ligamentum flavum is 5 to 6 mm thick in the midline, whereas in the thoracic
region it is 3 to 5 mm thick.
In the thoracic region, the depth from the skin to the epidural space depends on the degree of cephalad
angulation used for the paramedian approach as well as the body habitus of the patient.
In the cervical region the depth to the ligamentum flavum is approximately the same as that in the
lumbar region, 4 to 6 cm.
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Needle Puncture: Lumbar Epidural
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identify the midline structures, and the bony landmarks
If a single-shot epidural technique is chosen, a Crawford needle is appropriate; if a continuous catheter
technique is indicated, a Tuohy or other needle with a lateral-facing opening is chosen.
The midline approach is most often indicated for a lumbar epidural procedure.
The needle is slowly advanced until the change in tissue resistance is noted as the needle abuts the
ligamentum flavum.
At this point, a 3- to 5-mL glass syringe is filled with 2 mL of saline solution, and a small (0.25 mL) air
bubble is attached to the needle, and if the needle tip is in the substance of the ligamentum flavum, the
air bubble will be compressible. If the ligamentum flavum has not yet been reached, pressure on the
syringe plunger will not compress the air bubble.
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Once compression of the air bubble has been achieved, the needle is grasped with the nondominant hand
and pulled toward the epidural space, while the dominant hand (thumb) applies constant steady pressure
on the syringe plunger, thus compressing the air bubble. When the epidural space is entered, the pressure
applied to the syringe plunger will allow the solution to flow without resistance into the epidural space.
An alternative technique is the hanging-drop technique for identifying entry into the epidural space. In
this technique, when the needle is placed in the ligamentum flavum a drop of solution is introduced into
the hub of the needle. No syringe is attached, and when the needle is advanced into the epidural space,
the solution should be “sucked into” the space.
The incidence of unintentional intravenous cannulation with an epidural catheter may be decreased by
injecting 5 to 10 mL of solution before threading the catheter. If a catheter is inserted, it should be
inserted only 2 to 3 cm into the epidural space because threading it farther may increase the likelihood of
catheter malposition. Obstetric patients require catheters to be inserted to 3 to 5 cm into the epidural
space to minimize dislodgement during labor analgesia.
Needle Puncture: Thoracic Epidural
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In this technique, the paramedian approach is preferred because it allows easier access to the epidural
space because the spinous processes in the mid-thoracic region overlap each other from cephalad to
caudad.
The loss-of-resistance technique and insertion of the catheter are carried out in a manner identical to that
used for lumbar epidural block. Again, the hanging-drop technique is an alternative method of
identifying the thoracic epidural space, although the classic Bromage needle–syringe grip is my first
choice for the thoracic epidural block (Fig. 41-10).
Needle Puncture: Cervical Epidural
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In the cervical epidural technique, the patient is typically in a sitting position with the head bent forward
and supported on a table.
The spinous processes of the cervical vertebrae are nearly perpendicular to the long axis of the vertebral
column; thus, a midline technique is applicable for the cervical epidural block.
The most prominent vertebral spinous processes, those of C7 and T1, are identified with the neck flexed.
The second (index) and third fingers of the palpating hand straddle the space between C7 and T1, and
the epidural needle is slowly inserted in a plane approximately parallel to the floor (or parallel to the
long axis of the cervical vertebral spinous processes). Abutment of the needle onto the ligamentum
flavum will be appreciated at a depth similar to that seen in the lumbar epidural block (i.e., 3.5 to
5.5 cm), and needle placement is then performed using the loss-of-resistance technique as in the other
epidural methods. The hanging-drop method is also an option for identification of the cervical epidural
space.
Potential Problems

systemic toxicity resulting from intravenous injection of the intended epidural anesthetic
o One way to minimize intravenous injection of the pharmacologic doses of local anesthetic
needed for epidural anesthesia is to verify needle or catheter placement by administering a test
dose before the definitive epidural anesthetic injection. The current recommendation for the test
dose is 3 mL of local anesthetic solution containing 1:200,000 epinephrine (15 µg of
epinephrine).
o Even if the test dose is negative, the anesthesiologist should inject the epidural solution
incrementally, be vigilant for unintentional intravascular injection, and have all necessary
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equipment and drugs available to treat local anesthetic–induced systemic toxicity.
o
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Unintentional administration of an epidural dose into the spinal fluid.
o Blood pressure and heart rate should be supported pharmacologically and ventilation should be
assisted as indicated.
o Usually atropine and ephedrine will suffice to manage this situation, or at least will provide time
to administer more potent catecholamines. If the entire dose (20 to 25 mL) of local anesthetic is
administered into the cerebrospinal fluid, tracheal intubation and mechanical ventilation are
indicated because it will be approximately 1 to 2 hours before the patient can consistently
maintain adequate spontaneous ventilation.
o When epidural anesthesia is performed and a higher-than-expected block develops after a delay
of only 15 to 30 minutes, subdural placement of the local anesthetic must be considered.
Treatment is symptomatic, with the most difficult part involving recognition that a subdural
injection is possible.
If neurologic injury occurs after epidural anesthesia, a systematic approach to the problem is necessary.
The performance of cervical or thoracic epidural techniques demands special care with hand and needle
control because the spinal cord is immediately deep to the site of both these epidural blocks.
Epidural hematoma created with the needles or catheters.
o Concern about epidural hematoma formation is greater in patients who have been taking
antiplatelet drugs such as aspirin or who have been receiving preoperative anticoagulants.
o Perioperative anticoagulant regimens that demand special consideration are the use of low–
molecular-weight heparin (LMWH) or potent antiplatelet drugs concurrently with epidural block.
o It is currently recommended that no procedure, including withdrawal or manipulation of an
epidural catheter, should occur within 12 hours after a dose of LMWH, and the next dose of
LMWH should be delayed for at least 2 hours after atraumatic epidural needle or catheter
insertion or manipulation. The antiplatelet drugs (e.g., ticlopidine, clopidogrel, and platelet
glycoprotein IIb/IIIa receptor antagonists) are sometimes combined with aspirin and other
anticoagulants.
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
Post–dural puncture headache can result from epidural anesthesia when unintentional subarachnoid
puncture accompanies the technique.
o When using the larger-diameter epidural needles (18 and 19 gauge), it can be expected that at
least 50% of patients experiencing unintentional dural puncture will have a postoperative
headache
Pearls
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Epidural catheters can be malpositioned in a number of ways. If a catheter is inserted too far into the
epidural space, it can be routed out of foramina, resulting in patchy epidural block.
The catheter can also be inserted into the subdural or subarachnoid space or into an epidural vein.
Similarly, the use of epidural catheters may be complicated by a prominent dorsomedian connective
tissue band (epidural septum or fat pad), which is found in some patients.
Another means of facilitating the success of epidural anesthesia is to allow the block enough “soak time”
before beginning the surgical procedure.
There appears to be a plateau effect in the doses of epidural local anesthetics; that is, once a certain
quantity of local anesthetic has been injected, more of the same agent does not significantly increase the
block height but rather may make the block denser, perhaps improving quality.
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