Epidural Anesthesia Flashcards
Epidural Anesthesia
The epidural space is a collapsible, distensible reservoir through which drugs spread and are removed by
Diffusion
Vascular transport
Leakage
Epidural Anesthesia
Factors Affecting Epidural Block Height
Drug Factors
Volume - Dose > Concentration > Additives
Patient Factors
Elderly age - Pregnancy > Weight - Height - Pressure in adjacent body cavities
Procedure Factors
Level of injection > Patient position > Speed of injection<br></br>Needle orifice direction
Factors Affecting Epidural Block Height - Drug Factors
The most important drug-related factors that affect block height after the administration of local anesthetic in the epidural space are:
Volume
(1 to 2 mL of solution should be injected per segment to be blocked)
Total mass of injectate
Factors Affecting Epidural Block Height - Drug Factors
T/F: Additives such as bicarbonate, epinephrine, and opioids influence onset, quality, and duration of analgesia and anesthesia
True
Factors Affecting Epidural Block Height - Drug Factors
T/F: Additives such as bicarbonate, epinephrine, and opioids affect epidural spread
False
Additives such as bicarbonate, epinephrine, and opioids do not affect epidural spread
Rather, they influence onset, quality, and duration of analgesia and anesthesia
Factors Affecting Epidural Block Height - Patient Factors
Patient Factors that can influence epidural block height include:
Age - Height - Weight - Pregnancy - CPAP
Age
Age can influence epidural block height.
There appears to be a stronger correlation with age and block height in thoracic epidurals, with one study suggesting that <em>40% less volume is required in the elderly</em>
Possible reasons include decreased leakage of local anesthetic through intervertebral foramina, decreased compliance of the epidural space in the elderly resulting in greater spread, or an increased sensitivity of the nerves in the elderly.
Height
As with spinal anesthesia, it appears that only the extremes of patient height influence local anesthetic spread in the epidural space.
Weight
Weight is not well correlated with block height in the settings of either lumbar or thoracic epidural anesthesia.
Pregnancy
Less local anesthetic is required to produce the same epidural spread of anesthesia in pregnant patients.
Although this may be in part a result of engorgement of epidural veins secondary to increased abdominal pressure, the effect also occurs in early pregnancy.
CPAP
Also, continuous positive airway pressure increases the height of a thoracic epidural block.
Factors Affecting Epidural Block Height - Procedure Factors
Procedure Factors that can influence epidural block height include:
Level of injection
Patient position
Factors Affecting Epidural Block Height - Procedure Factors
Procedure Factors that can influence epidural block height include:
Level of injection
The level of injection is the most important procedural-related factor that affects epidural block height.
In the upper cervical region, spread of injectate is mostly caudal, in the midthoracic region spread is equally cephalad and caudal, and in the low thoracic region spread is primarily cephalad.
After a lumbar epidural, spread is more cephalad than caudal.
Some studies suggest that the total number of segments blocked is less in the lumbar region compared with thoracic levels for a given volume of injectate.
Patient position
Patient position has been shown to affect spread of lumbar epidural injections, with preferential spread and faster onset to the dependent side in the lateral decubitus position.
The sitting and supine positions do not affect epidural block height. However, the head-down tilt position does increase spread in obstetric patients.
Factors Affecting Epidural Block Height - Procedure Factors
T/F: Needle bevel direction and speed of injection appear to influence the spread of a bolus injection.
False
Needle bevel direction and speed of injection do not appear to influence the spread of a bolus injection.
Pharmacology - Local anesthetics for epidural use
Local anesthetics for epidural use may be classified into
short-, intermediate-, and long-acting drugs.
Pharmacology - Local anesthetics for epidural use
How long does a single bolus dose of local anesthetic in the epidural space provide surgical anesthesia?
45 minutes up to 4 hours
This depends on the type of local anesthetic administered and the use of any additives
Pharmacology - Local anesthetics for epidural use
Most commonly, why is an epidural catheter left in situ?
To provide indefinite extension of local anesthetic–based anesthesia or regular analgesia
Short-Acting and Intermediate-Acting Local Anesthetics
Procaine
Chloroprocaine
Articaine
Lidocaine
Prilocaine
Mepivacaine
Short-Acting and Intermediate-Acting Local Anesthetics
Similar to spinal anesthesia, 5% procaine is Not commonly used for epidural anesthesia - why not?
Slow onset
Unreliable Block
Poor quality Block
Short-Acting and Intermediate-Acting Local Anesthetics
Chloroprocaine is available preservative free in 2% and 3% concentrations for epidural injection - which concentration is preferable for surgical anesthesia?
Chloroprocaine 3%
Chloroprocaine 3% is preferable for surgical anesthesia because the former may not produce muscle relaxation
Short-Acting and Intermediate-Acting Local Anesthetics
Chloroprocaine 3% preparation has an onset time of … and a duration of …
10 to 15 minutes (Onset time)
Up to 60 minutes (Duration)
Short-Acting and Intermediate-Acting Local Anesthetics
Adding epinephrine to Chloroprocaine 3% preparation prolongs the block for …
up to 90 minutes
Short-Acting and Intermediate-Acting Local Anesthetics
Before the development of preservative-free preparations, large volumes (>25 mL) of chloroprocaine had been associated with:
Deep, aching, burning Lumbar back pain
This was thought to be secondary to the <em><strong>ethylene-di-amine-tetra-acetic acid</strong></em> that chelated calcium and caused a localized <em><strong>hypocalcemia</strong></em>
Short-Acting and Intermediate-Acting Local Anesthetics
Chloroprocaine can antagonize the effects of epidural morphine - This may be a result of
Opioid receptor antagonism
by either the chloroprocaine or a metabolite
Antagonism of an intracellular messenger and decreased morphine availability caused by a reduction in perineural pH are also proposed mechanisms
Short-Acting and Intermediate-Acting Local Anesthetics
Morphine and chloroprocaine seem like an illogical combination because
The beneficial ultra-short duration of action of chloroprocaine
is offset by the addition of morphine
Short-Acting and Intermediate-Acting Local Anesthetics
Articaine is not widely used for epidural anesthesia and has not been studied extensively. How does 2% articaine compare with epidural lidocaine?
Similar latency, spread, duration, and motor block
It has also been used for obstetric epidural analgesia
Short-Acting and Intermediate-Acting Local Anesthetics
Lidocaine is available in 1% and 2% solutions; it has an onset time of … and a duration of …
10 to 15 minutes (onset time)
up to 120 minutes (duration)
Short-Acting and Intermediate-Acting Local Anesthetics
Lidocaine is available in 1% and 2% solutions; it has an onset time of 10 to 15 minutes and a duration of up to 120 minutes, which can be extended to 180 minutes with the addition of
Epinephrine
Short-Acting and Intermediate-Acting Local Anesthetics
T/F: Transient neurologic symptoms (TNS) is commonly associated with epidural lidocaine.
False
Transient neurologic symptoms (TNS) is associated with spinal lidocaine
Short-Acting and Intermediate-Acting Local Anesthetics
Prilocaine is available in 2% and 3% solutions. The 2% solution produces a sensory block with minimal motor block. Onset time is approximately … , with a duration of approximately …
Prilocaine
15 minutes (Onset time)
100 minutes (duration)
Short-Acting and Intermediate-Acting Local Anesthetics
Which has a more marked sensory blockade and a longer duration?
A. lidocaine
B. prilocaine
A. lidocaine
B. prilocaine
Short-Acting and Intermediate-Acting Local Anesthetics
In large doses, prilocaine is associated with
Methemoglobinemia
Short-Acting and Intermediate-Acting Local Anesthetics
Mepivacaine is available as 1%, 1.5%, and 2% preservative-free solutions. The 2% preparation has an onset time similar to lidocaine of approximately … but a slightly longer duration of …
Mepivacaine
15 minutes (onset time)
a slightly longer duration vs Lidocaine
(up to 200 minutes with epinephrine),
Making it a preferred option by some centers for surgery of an intermediate duration
Long-Acting Local Anesthetics
Ropivacaine
Bupivacaine
Levobupivacaine
Tetracaine
R-BLT
Long-Acting Local Anesthetics
Tetracaine is not widely used for epidural anesthesia because of:
Unreliable block height
Systemic toxicity (in larger doses)
Long-Acting Local Anesthetics
Bupivacaine is available in 0.25%, 0.5%, or 0.75% preservative-free solutions. The onset time is around … with a duration of …
Bupivacaine
20 minutes (onset time)
up to 225 minutes (duration)
Long-Acting Local Anesthetics
Bupivacaine duration is prolonged only slightly by the addition of … to …. minutes.
Epinephrine
(to 240 minutes)
Long-Acting Local Anesthetics
More dilute concentrations of Bupivacaine such as 0.125% to 0.25% can be used for
Analgesia
Long-Acting Local Anesthetics
Long-Acting Local Anesthetics complications from using more diluted concentrations of Bupivacaine such as 0.125% to 0.25% include:
Cardiac and central nervous system toxicity
Potential for motor block (larger doses)
Long-Acting Local Anesthetics
Bupivacaine solutions of 0.5% and 0.75% are used to provide
Surgical anesthesia
Long-Acting Local Anesthetics
Which version of bupivacaine is currently under investigation for epidural use?
Liposomal Bupivacaine
An epidural bolus of liposomal 0.5% bupivacaine provided similar onset but longer-lasting analgesia to boluses of plain bupivacaine
Long-Acting Local Anesthetics
T/F: Liposomal Bupivacaine appears to be more toxic than plain bupivacaine or to have a differing cardiac safety profile
False
Liposomal Bupivacaine does not appear to be more toxic than plain bupivacaine or to have a differing cardiac safety profile
Long-Acting Local Anesthetics
The benefit of Liposomal Bupivacaine, as with extended-release morphine is
Lack of need for an epidural catheter
Conversely, such extended-release boluses are less titratable if for any reason the epidural needs to be terminated early
Long-Acting Local Anesthetics
Which concentrations of Levobupivacaine can be used as an epidural local anesthetic for surgical anesthesia?
Levobupivacaine
0.5% to 0.75% concentrations
(for surgical anesthesia)
Long-Acting Local Anesthetics
Which concentrations of Levobupivacaine can be used as an epidural local anesthetic for analgesia ?
Levobupivacaine
Concentrations of 0.125% to 0.25%
(for analgesia)
Long-Acting Local Anesthetics
Levobupivacaine administered epidurally has the same clinical characteristics as bupivacaine. The advantage of levobupivacaine over bupivacaine is that:
levobupivacaine is less cardiotoxic compared with bupivacaine
Long-Acting Local Anesthetics
Ropivacaine is available in 0.2%, 0.5%, 0.75%, and 1.0% preservative-free preparations - Which concentration are used for surgical anesthesia?
Ropivacaine
0.5% to 1.0%
(for surgical anesthesia)
Long-Acting Local Anesthetics
Ropivacaine is available in 0.2%, 0.5%, 0.75%, and 1.0% preservative-free preparations - Which concentration are used for analgesia?
Ropivacaine
0.1% to 0.2 %
(for analgesia)
Long-Acting Local Anesthetics
Which is associated with a superior safety profile?
A. Ropivacaine
B. Bupivacaine
A. Ropivacaine
<strong>(</strong>Ropivacaine is also less cardiotoxic)
B. Bupivacaine
Data from animal models suggest that Bupivacaine has a 1.5 to 2.5 lower seizure threshold than Ropivacaine
Long-Acting Local Anesthetics
T/F: When compared with bupivacaine and levobupivacaine, ropivacaine at equivalent concentrations has a relatively similar clinical profile
True
Ropivacaine has a slightly shorter duration of action and less motor block, although the reduced motor block may in fact reflect different potencies of the drugs rather than a true motor-sparing effect of ropivacaine
Epidurally administered ropivacaine is 40% less potent than bupivacaine.
Epidural Additives
Vasoconstrictors
Opioids
α2-Agonists
Other Drugs
Carbonation and Bicarbonate
Epidural Additives - Vasoconstrictors
Epinephrine
Epinephrine reduces vascular absorption of local anesthetics in the epidural space
The local anesthetics vary in their responsiveness to epinephrine
The effect is the most with lidocaine, mepivacaine, and chloroprocaine (up to 50% prolongation), with a lesser effect with bupivacaine, levobupivacaine, and etidocaine, and a limited effect with ropivacaine, which already has intrinsic vasoconstrictive properties
Epinephrine itself may also have some analgesic benefits because it is absorbed into the CSF, where it can act on dorsal horn α2 receptors
Phenylephrine
Phenylephrine has been used in epidural anesthesia less widely than in spinal anesthesia, perhaps because it does not reduce peak blood levels of local anesthetic as effectively as epinephrine does during epidural use
Epidural Additives - Opioids
Benefit of opioids:
Synergistically enhance the analgesic effects of epidural local anesthetics, without prolonging motor block
A combination of local anesthetic and opioid reduces the dose-related adverse effects of each drug independently
The analgesic benefits of neuraxial opioids must be balanced against the dose-dependent side effects
Epidural Additives - Opioids
Ceiling effect of epidural opioids
As with intrathecal opioids, there appears to be a therapeutic ceiling effect above which only side effects increase
Epidural Additives - Opioids
Opioids may also be used alone, particularly when there are concerns regarding
Hemodynamic instability
Epidural Additives - Opioids
How do Epidural opioids work?
By crossing the dura and arachnoid membrane
to reach the CSF and spinal cord dorsal horn
Epidural Additives - Opioids
Why are Lipophilic opioids, such as fentanyl and sufentanil found in lower concentrations in CSF than hydrophilic opioids, such as morphine and hydromorphone?
They partition into epidural fat
Epidural Additives - Opioids
What’s the principal analgesic mechanism of Fentanyl and sufentanil (Lipophilic opioids)?
Readily absorbed into the systemic circulation
Epidural Additives - Opioids
Epidural morphine is administered as a bolus of …, with an onset time of … and duration of …
Epidural morphine
1 to 5 mg (bolus dose)
30 to 60 minutes (onset time)
up to 24 hours (duration)
Epidural Additives - Opioids
The optimal dose of Epidural morphine that balances analgesia while minimizing side effects is
Epidural morphine
2.5 to 3.75 mg
(Optimal dose that balances analgesia while minimizing side effects)
Epidural Additives - Opioids
At what dose can morphine be administered continuously through an epidural catheter?
Morphine epidural catheter infusion
0.1 to 0.4 mg/hr
Epidural Additives - Opioids
Which is more hydrophilic?
A. Hydromorphone
B. Fentanyl
A. Hydromorphone
B. Fentanyl
Epidural Additives - Opioids
Which is more lipophilic?
A. Hydromorphone
B. Morphine
A. Hydromorphone
B. Morphine
Epidural Additives - Opioids
Hydromorphone can be administered as a bolus of …, with onset at …. minutes and a duration of ….
Hydromorphone
0.4 to 1.5 mg (bolus dose)
15 to 30 minutes (onset time)
18 hours (duration)
Epidural Additives - Opioids
Hydromorphone used as an infusion is delivered at what rate?
Hydromorphone
5 and 20 μg/hr (infusion rate)
Epidural Additives - Opioids
The onset of epidural fentanyl and sufentanil is … and lasts only…
Epidural fentanyl & sufentanil
5 to 15 minutes (onset)
2 to 3 hours (duration)
Epidural Additives - Opioids
Which bolus doses of Epidural fentanyl & sufentanil may be used to provide analgesia?
Epidural fentanyl & sufentanil
Bolus doses of 10 to 100 μg (analgesia)
Epidural Additives - Opioids
Diamorphine is available in the United Kingdom and used in doses of … as epidural boluses, or approximately … in an infusion
Diamorphine
2 to 3 mg (epidural bolus)
0.05 mg/mL (infusion)
Epidural Additives - Opioids
The extended-release liposomal formulation of morphine used as a single-shot lumbar epidural dose, thereby avoiding issues and side effects of a continuous local anesthetic infusion and indwelling catheters, particularly in patients receiving anticoagulants is also known as:
Depodur
Epidural Additives - Opioids
When administered before surgery (or after clamping of the cord in cesarean deliveries), Depodur can provide pain relief for how long?
up to 48 hours
Epidural Additives - Opioids
What dose of Depodur is recommended for lower abdominal surgery
Depodur
10 to 15 mg
(lower abdominal surgery)
Epidural Additives - Opioids
What dose of Depodur is recommendedfor major lower limb orthopedic surgery?
Depodur
15 mg
(major lower limb orthopedic surgery)
Epidural Additives - α2-Agonists
Clonidine
Epidural clonidine can prolong sensory block to a greater extent than motor block
The mechanism appears to be mediated by the opening of potassium channels and subsequent membrane hyperpolarization rather than an α2-agonist effect
The addition of clonidine reduces both epidural local anesthetic and opioid requirements
Other benefits of clonidine may include a reduced immune stress and cytokine response
Epidural clonidine does have a variety of side effects including hypotension, bradycardia, dry mouth, and sedation
The cardiovascular effects may be greatest when clonidine is administered in the epidural space at the thoracic level
Dexmedetomidine
In preliminary studies, epidural dexmedetomidine has also been shown to reduce intraoperative anesthetic requirements, improve postoperative analgesia, and prolong both sensory and motor block
Epidural Additives - Other Drugs
Ketamine
Conflicting reports exist regarding the benefit of epidural ketamine and whether it is neurotoxic
Neostigmine
Epidural neostigmine provides labor analgesia before local anesthetic infusion without causing respiratory depression, hypotension, or motor impairment
Midazolam - Tramadol - Dexamethasone - Droperidol
Have also been studied but are not commonly used
Epidural Additives - Carbonation and Bicarbonate
Many local anesthetic preparations have a pH between 3.5 and 5.5 for chemical stability and bacteriostasis
At these low pHs, a higher proportion of the drug is in the ionized form and is therefore unable to cross nerve membranes to reach the internal binding site on sodium channels
Both carbonation of the solution and adding bicarbonate have been used in an attempt to increase the solution pH, and therefore the non-ionized free-base proportion of local anesthetic
Although carbonation may theoretically increase the speed of onset and quality of the block by producing more rapid intraneural diffusion and more rapid penetration of connective tissue surrounding the nerve trunk, available data suggest that there are no clinical advantages for carbonated solutions
Epidural Technique
Preparation
Position
Projection and Puncture
Paramedian Approach
Epidural Technique - Preparation
Patient preparation
Patient preparation as previously described for spinal anesthesia must equally be applied to epidural anesthesia, namely consent, monitoring, and resuscitation equipment, intravenous access, and choosing the patient and drugs appropriately depending on comorbidities and the nature of surgery
Sterility
Sterility is arguably even more important than spinal anesthesia because a catheter is often left in situ
Surgical field
The extent of the surgical field must be understood so that the epidural may be inserted at the appropriate level—that is, the lumbar, low-, mid-, or high-thoracic, or less commonly, cervical
Epidural needles
A variety of epidural needles have been used for epidural anesthesia, but Tuohy needles are most common
These needles are usually 16 to 18 g in size and have a 15- to 30-degree curved, blunt “Huber” tip designed to both reduce the risk of accidental dural puncture and guide the catheter cephalad
The needle shaft is marked in 1-cm intervals so that depth of insertion can be identified
Epidural catheter
The catheter is made of a flexible, calibrated, durable, radiopaque plastic with either a single end hole or multiple side orifices near the tip
Several investigators have found that multiple-orifice catheters are superior, with a reduced incidence of inadequate analgesia
However, the use of multiorifice catheters in pregnant women resulted in a more frequent incidence of epidural vein cannulation
Method identifying the epidural space
The method of identifying the epidural space must also be predetermined
Most practitioners use a loss-of-resistance technique to either air or saline, rather than the hanging drop technique, both of which are described later
If a loss-of-resistance technique is used, an additional decision about the type of syringe (i.e., glass versus low-resistance plastic and Luer-Lok versus friction hub) is required
Epidural Technique - Position
The sitting and lateral decubitus positions necessary for epidural puncture are the same as those for spinal anesthesia
As before, inadequate positioning of the patient can complicate an otherwise meticulous technique
Shorter insertion times occur in the sitting position for thoracic epidurals compared with the lateral decubitus position, but ultimately, success rates are comparable
As with spinal anesthesia, epidurals are performed with the patient awake
Epidural Technique - Projection and Puncture
The level of needle insertion depends on:
Location of surgery
Epidural Technique - Projection and Puncture
Important surface landmarks needle insertion include:
Vertebra prominens
(C7)
Root of the scapular spine
(T3)
Inferior angle of the scapula
(corresponding to the T7 vertebral body)
Intercristal line
(corresponding to the L4-L5 interspace)
Epidural Technique - Projection and Puncture
Ultrasonography may be useful to identify the correct thoracic space; it is less commonly used for thoracic epidural insertion, however, because
Acoustic shadows make visualization of landmarks such as the ligamentum flavum and intrathecal space more difficult
Epidural Technique - Projection and Puncture
A variety of different needle approaches exist, including:
Midline
Paramedian
Modified paramedian (Taylor approach)
Caudal
Epidural Technique - Projection and Puncture
Suggested Epidural Insertion Sites for Hip surgery, Lower extremity, Obstetric analgesia:
Lumbar L2-L5
Epidural Technique - Projection and Puncture
Suggested Epidural Insertion Sites for Colectomy, Anterior resection
Upper abdominal surgery:
T6-T8
Lower thoracic
Spread more cranial than caudal
Epidural Technique - Projection and Puncture
Suggested Epidural Insertion Sites for Thoracic Surgical Procedures
T2-T6
Midpoint of surgical incision
Epidural Technique - Projection and Puncture
Which needle approch approach is commonly chosen for lumbar and low thoracic approaches
Midline approach
Epidural Technique - Projection and Puncture
Describe the Midline approach?
After local anesthetic infiltration of the skin, the nondominant hand can be rested on the back of the patient, with the thumb and index finger holding the needle hub or wing
The angle of approach should be only slightly cephalad in the lumbar and low-thoracic regions, whereas in the midthoracic region, the approach should be more cephalad because of the significant downward angulation of the spinous processes
In a controlled fashion, the needle should be advanced with the stylet in place through the supraspinous ligament and into the interspinous ligament, at which point the stylet can be removed and the syringe attached
Needle should rest firmly in the tissues if in the correct place
Epidural Technique - Projection and Puncture
Which methods could be used to confirm needle placement in the ligamentum of flavum?
Loss-of-resistance method
Hanging-drop method
Recommended before attaching the syringe, but this may be difficult, particularly for novices; however, this may allow an improved appreciation of epidural anatomy for the operator
Epidural Technique - Projection and Puncture
If the needle is merely inserted into the supraspinous ligament and then loss-of-resistance or hanging-drop insertion is begun, there is an increased chance of
False loss-of-resistance
Possibly because of defects in the interspinous ligament
Such false-positive rates can be as high as 30%.
Epidural Technique - Projection and Puncture
Two most non-compressible media used to detect lost of resistance when identigying the epidural space
Air or saline
Each involves intermittent (for air) or constant (for saline) gentle pressure applied to the bulb of the syringe with the dominant thumb while the needle is advanced with the nondominant hand
A combination of air and saline may also be used, incorporating 2 mL of saline and a small (0.25 mL) air bubble
Epidural Technique - Projection and Puncture
Which structure is usually identified as a tougher structure with increased resistance, and when the epidural space is subsequently entered, the pressure applied to the syringe plunger allows the solution to flow without resistance into the epidural space
Ligamentum flavum
Epidural Technique - Projection and Puncture
There are reports that air is less reliable in identifying the epidural space - Why?
Results in a higher chance of Incomplete block
May also cause both Pneumocephalus
(which can result in headaches)
Venous air embolism in rare cases
If air is chosen, the amount of air injected after loss-of-resistance should therefore be minimized
Epidural Technique - Projection and Puncture
T/F: A recent meta-analysis suggested that there was no difference in adverse outcome in the obstetric population when air or saline was used to confirm needle placement
True
Epidural Technique - Projection and Puncture
T/F: Fluid inserted through the epidural needle before catheter insertion reduces the risk of epidural vein cannulation by the catheter
True
Epidural Technique - Projection and Puncture
What’s a disadvantage of using saline to identify the epidural space?
More difficult to readily detect an accidental dural puncture
Epidural Technique - Projection and Puncture
An alternative method of identifying the epidural space whereby After the needle is placed into the ligamentum flavum, a drop of solution such as saline is placed within the hub of the needle. When the needle is advanced into the epidural space, the solution should be “sucked in.” This method is known as:
Hanging-drop technique
The theory behind this maneuver has traditionally been attributed to subatmospheric pressure in the epidural space, although recent experimental evidence in the cervical region suggests that using negative-pressure methods are poorly reliable and only useful in the sitting position
The subatmospheric pressure has been related to expansion of the epidural space as the needle pushes the dura away from the ligamentum flavum
The negative intrathoracic pressure may influence the pressure in the epidural space in the thoracic region and should be maximal during inspiration
Timing needle advancement to coincide with inspiration may be difficult, however.
Epidural Technique - Projection and Puncture
When a lumbar midline approach is used, the depth from skin to the ligamentum flavum commonly reaches
4 cm
with the depth in most (80%) patients being between 3.5 and 6 cm; it can be longer or shorter in obese or very thin patients, respectively
Ultrasonography may be useful to predict the depth before needle insertion
In the lumbar region, the ligamentum flavum is 5 to 6 mm thick in the midline
Epidural Technique - Projection and Puncture
When a thoracic approach is chosen, needle control is of equal or greater importance because
injury to the spinal cord is possible if the needle is advanced too far
Epidural Technique - Projection and Puncture
T/F: There are no data to suggest that approaching the epidural space at the lumbar level is any more or less safe than at the thoracic level
True
This may be partly because those using the thoracic technique are most often anesthesiologists with considerable experience in lumbar epidural anesthesia
In addition, the increased angle of needle insertion in the thoracic region may theoretically provide an element of safety in that the more acute angle necessary to gain access to the epidural space provides some margin of safety
Epidural Technique - Projection and Puncture
When the epidural space is identified, the depth of the needle at the skin should be noted - How should the syringe and the catheter be then manipulated?
The syringe can then be removed and a catheter gently threaded to approximately the 15- to 18-cm mark to ensure a sufficient length has entered the epidural space
The needle can then be carefully withdrawn, and the catheter is withdrawn to leave 4 to 6 cm in the space
Epidural Technique - Projection and Puncture
What risks are associated with catheter space less than 4 cm in length in the epidural space?
Catheter dislodgement
Inadequate analgesia
Epidural Technique - Projection and Puncture
Threading more catheter may increase the likelihood of:
Catheter malposition or complications
Epidural Technique - Projection and Puncture
What is one of the causes of a failed block
False loss-of-resistance
As described earlier, a false loss-of-resistance can occur and is one of the causes of a failed block
Epidural Technique - Projection and Puncture
The test that stimulates the spinal nerve roots with a low electrical current conducted through normal saline in the epidural space and an electrically conducting catheter is also known as:
Tsui test
The Tsui test may be used to confirm the epidural catheter position
Epidural Technique - Projection and Puncture
How is the Tsui test performed?
A metal-containing catheter must be used, with the cathode lead of the nerve stimulator connected to the catheter via an electrode adapter, whereas the anode lead is connected to an electrode on the patient’s skin
At currents of approximately 1 to 10 mA, corresponding muscle twitches (i.e., intercostal or abdominal wall muscles for thoracic epidural catheters) can be used to identify catheter tip location
Subarachnoid and subdurally positioned epidural catheters elicit motor responses at a much lower threshold current (<1 mA), because the stimulating catheter is in very close or direct contact with highly conductive CSF
Epidural Technique - Projection and Puncture
When the catheter is positioned at the desired depth, it must be secured to the skin - How is this achieved?
Commercial fixation devices
Commercial fixation devices exist, and some are superior to tape alone
Tunneling
Tunneling can reduce catheter migration and improve lasting block success
However, tunneling has not been compared with noninvasive catheter fixation devices in a welldesigned study
Epidural Technique
Which approach is particularly useful in the mid- to high thoracic region, where the angulation of the spine and the narrow spaces render the midline approach problematic
Paramedian approach
Epidural Technique - Paramedian approach
Describe the Paramedian approach
The needle should be inserted 1 to 2 cm lateral to the inferior tip of the spinous process corresponding to the vertebra above the desired interspace
The needle is then advanced horizontally until the lamina is reached and then redirected medially and cephalad to enter the epidural space
Epidural Technique - Paramedian approach
The modified paramedian approach via the L5-S1 interspace, which may be useful in trauma patients who cannot tolerate or are not able to maintain a sitting position is also known as
Taylor approach
The needle is inserted 1 cm medial and 1 cm inferior to the posterior superior iliac spine and is angled medially and cephalad at a 45- to 55-degree angle.
Epidural Technique - Paramedian approach
Before initiating an epidural local anesthetic infusion, a test dose may be administered - The purpose of this is:
To Exclude intrathecal or intravascular catheter placement
A small volume of lidocaine 1.5% with epinephrine is traditionally used for this purpose
Epidural Technique - Paramedian approach
What’s the best pharmacologic method of detecting intravascular placement of epidural catheter?
A recent systematic review found reasonable evidence that 10 to 15 μg of epinephrine alone in nonpregnant adult patients was the best pharmacologic method of detecting intravascular placement
Endpoints of an increase in systolic blood pressure more than 15 mm Hg or an increase in heart rate more than 10 beats/min may be used
Epidural Technique - Paramedian approach
What’s the optimal method of detecting intrathecal or subdural catheter placement?
Could not be ascertained
