Epidural anesthesia factors affecting height and local anesthetic used
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Soli Deo Gloria . Epidural Anesthesia: Factors Affecting Height and Local Anesthetic Used . Developing Countries Regional Anesthesia Lecture Series Daniel D. Moos CRNA, Ed.D . U.S.A [email protected] Lecture 11. Disclaimer.

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Epidural anesthesia factors affecting height and local anesthetic used l.jpg

Soli Deo Gloria

Epidural Anesthesia: Factors Affecting Height and Local Anesthetic Used

Developing Countries Regional Anesthesia Lecture Series

Daniel D. Moos CRNA, Ed.D. U.S.A [email protected]

Lecture 11


Disclaimer l.jpg
Disclaimer

  • Doses are only general recommendations. There are several factors that may result in either an inadequate or high epidural block.

  • Every effort was made to ensure that material and information contained in this presentation are correct and up-to-date. The author can not accept liability/responsibility from errors that may occur from the use of this information. It is up to each clinician to ensure that they provide safe anesthetic care to their patients.


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Introduction to Epidural Anesthesia

  • Epidural anesthesia produces a reversible loss of sensation and motor function much like a spinal with the exception that local anesthetic is placed within the epidural space.

  • Larger doses of local anesthetic are required to produce anesthesia when compared to a spinal anesthetic.

  • Doses must be monitored to avoid toxicity.


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Introduction to Epidural Anesthesia

  • An epidural catheter allows the versatility to extend the duration of anesthesia beyond the original dose by the administration of additional local anesthetic.

  • Epidural catheters may be left in place for postoperative analgesia.


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Epidural Anesthesia Indications

  • Cesarean section

  • Procedures of the uterus, perineum*

  • Hernia repairs

  • Genitourinary procedures

  • Lower extremity orthopedic procedures

  • Excellent choice for elderly or those who may not tolerate a general anesthetic


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Epidural Anesthesia

  • Should NOT be used in patients who are hypovolemic or severely dehydrated.

  • Patients should be pre-hydrated with .5 – 1 liter of crystalloid solutions (i.e. ringers lactate) immediately prior to the block.


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Epidural Anesthesia

  • Higher failure rate for procedures of the perineum.

  • Lower lumbar and sacral nerve roots are large and there is an increased amount of epidural fat which may affect local anesthetic penetration and blockade.

  • This is known as sacral sparing.


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Epidural Anesthesia Advantages

  • Easy to perform (though it takes a bit more practice than spinal anesthesia)

  • Reliable form of anesthesia

  • Provides excellent operating conditions

  • The ability to administer additional local anesthetics increasing duration

  • The ability to use the epidural catheter for postoperative analgesia


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Epidural Anesthesia Advantages

  • Return of gastrointestinal function generally occurs faster than with general anesthesia

  • Patent airway

  • Fewer pulmonary complications compared to general anesthesia

  • Decreased incidence of deep vein thrombosis and pulmonary emboli formation compared to general anesthesia


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Epidural Anesthesia Disadvantages

  • Risk of block failure. The rate of failure is slightly higher than with a spinal anesthetic. Always be prepared to induce general anesthesia if block failure occurs.

  • Onset is slower than with spinal anesthesia. May not be a good technique if the surgeon is impatient or there is little time to properly perform the procedure.


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Epidural Anesthesia Disadvantages

  • Normal alteration in the patient’s blood pressure and potentially heart rate (generally slower onset with less alteration in blood pressure and heart rate than with a spinal anesthetic). It is essential to place the epidural block in the operating room/preoperative area with monitoring of an ECG, blood pressure, and pulse oximetry. Resuscitation medications/equipment should be available.

  • Risk of complications as outlined in Introduction to Neuraxial Blockade chapter. There is an increase in the complication rate compared to spinal anesthesia.


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Epidural Anesthesia Disadvantages

  • Continuous epidural catheters should not be used on the ward if the patient’s vital signs are NOT closely monitored.

  • Risk for infection, resulting in serious complications.


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Absolute Contraindications Epidural

  • Patient refusal

  • Infection at the site of injection

  • Coagulopathy

  • Severe hypovolemia

  • Increased Intracranial pressure

  • Severe Aortic Stenosis

  • Severe Mitral Stenosis

  • Ischemic Hypertrophic Sub-aortic Stenosis


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Relative Contraindications

  • Sepsis

  • Uncooperative patients

  • Pre-existing neuro deficits/neurological deficits

  • Demylenating lesions

  • Stenotic valuvular heart lesions (mild to moderate Aortic Stenosis/Ischemic Hypertrophic Sub-aortic Stenosis)

  • Severe spinal deformities


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Controversial

  • Prior back surgery

  • Inability to communicate with the patient

  • Complicated surgeries that may involved prolonged periods of time to perform, major blood loss, maneuvers that may complicate respiration


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Mechanism/Site of Action

  • Administered at a physiologic distance when compared to spinal anesthesia. The intended targets are the spinal nerves and associated nerve roots.

  • Several barriers to the spread of local anesthetic to the intended site of action results in the requirement of larger volumes of local anesthetic when compared to spinal anesthesia.


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Barriers

  • Dura mater between the epidural space and spinal nerve and nerve roots act as a modest barrier.

  • The majority of the solutions is absorbed systemically through the venous rich epidural space.

  • Epidural fatty tissue acts as a reservoir.

  • The remainder reaches the spinal nerve and nerve roots.


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Spread of Local Anesthetic in the Epidural Space

  • Local anesthetic injected into the epidural space moves in a horizontal and longitudinal manner.

  • Theoretically the longitudinal spread could reach the foramen magnum and sacral foramina if enough volume was injected.



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Spread of Local Anesthetics- Horizontal

  • Horizontally the local anesthetic spreads through the intervertebral foramina to the dural cuff.

  • Local anesthetics spread through the dural cuff via the arachnoid villa and into the CSF.

  • Blockade occurs at the mixed spinal nerves, dorsal root ganglia, and to a small extent the spinal cord.




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Distribution, Uptake & Elimination to CSF via arachnoid granules

  • Takes 6-8 times the dose of a spinal anesthetic to create a comparable block.


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This is due to: to CSF via arachnoid granules

  • Larger mixed nerves are found in the epidural space when compared to the subarachnoid space.

  • Local anesthetics must penetrate arachnoid and dura mater.

  • Local anesthetics are lipid soluble and will be absorbed by tissue and epidural fat.

  • Epidural veins absorb a significant amount of local anesthetic with blood concentrations peaking in 10-30 minutes after a bolus.


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Distribution, Uptake & Elimination to CSF via arachnoid granules

  • Local anesthetics absorbed in the epidural veins will be diluted in the blood.

  • The pulmonary systems acts as a temporary buffer and protects other organs from the toxic effects of local anesthetics.

  • Distribution occurs to the vessel rich organs, muscle, and fat.


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Distribution, Uptake & Elimination to CSF via arachnoid granules

  • Long acting amides will bind to alpha-1 globulins which have a high affinity to local anesthetics but become rapidly saturated.

  • Amides are metabolized in the liver and excreted by the kidneys.

  • Esters are metabolized by pseudocholinesterase so rapidly that there are rarely significant plasma levels.


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Factors Affecting Height of Epidural Blockade to CSF via arachnoid granules

  • Volume of local anesthetic

  • Age

  • Height of the patient

  • Gravity


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Volume to CSF via arachnoid granules

  • Can be variable

  • General rule: 1-2 ml of local anesthetic per dermatome

  • i.e. epidural placed at L4-L5; you want a T4 block for a C-sec. You have 4 lumbar dermatomes and 8 thoracic dermatomes. 12 dermatomes X 1-2 ml = 12-24 ml

  • Big range! Stresses importance of incremental dosing!


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Volume to CSF via arachnoid granules

  • If you require only segmental anesthesia than the dose would be less.

  • Volume of local anesthetic plays a critical role in block height.

  • Dose of local anesthetics administered in thoracic area should be decreased by 30-50% due to decrease in compliance and volume.


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Age to CSF via arachnoid granules

  • As age increases the amount of local anesthetic to achieve the same level of anesthesia decreases. A 20 year old vs 80 year old

  • This is due to changes in size and compliance of the epidural space


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Height to CSF via arachnoid granules

  • The shorter the patient the less local anesthetic required.

  • A patient that is only 5’3” may require 1 ml per dermatome while someone who is 6’3” may require the full 2 ml per dermatome


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Gravity to CSF via arachnoid granules

  • Position of patient does affect spread and height of local anesthetic BUT not to the point of spinal anesthesia.

  • i.e. lateral decubitus position will “concentrate” more local anesthetic to the dependent side will a weaker block will occur in the non-dependent area.

  • A sitting patient will have more local anesthetic delivered to the lower lumbar and sacral dermatomes


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Gravity to CSF via arachnoid granules

  • L5-S2 sometimes will have ‘patchy’ anesthesia due to sparing. By having the patient “sitting” or in a semifowlers position one can concentrate local anesthetic to this area.

  • Trendelenberg or reverse trendelenberg may help spread local anesthetic cephalad or alternatively limit the spread.


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Local Anesthetics used for Epidural Anesthesia to CSF via arachnoid granules


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Considerations in choosing to CSF via arachnoid granules

  • Understanding of local anesthetic potency & duration

  • Surgical requirements and duration of surgery

  • Postoperative analgesic requirements


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Local Anesthetics for Epidural Anesthesia to CSF via arachnoid granules

  • Use only preservative free solutions

  • Read the labels, ensure that it is preservative free or prepared for epidural/caudal anesthesia/analgesia


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Categories according to duration of action to CSF via arachnoid granules

  • Short Acting: 2-chloroprocaine

  • Intermediate Acting: lidocaine and mepivacaine

  • Long Acting: bupivacaine, etidocaine, ropivacaine, levobupivacaine


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Short Acting 2-chloroprocaine to CSF via arachnoid granules

  • Ester local anesthetic

  • Initially associated with disconcerting neurotoxicity (adhesive arachnoiditis) when administered in the intrathecal space (inadvertently)

  • Attributed to bisulfate concentrations


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Short Acting 2-chloroprocaine to CSF via arachnoid granules

  • 1985 bisulfate content decreased

  • 1987 preservative free solution introduced

  • 1996 bisulfate free solution available

  • Since the change in formulation no more reports of neurotoxity.

  • However the other preparations may be available so you need to read labels!

  • Large volumes of local anesthetic injected inadvertently into the subarachnoid space may still cause neurotoxicity


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Short Acting 2-chloroprocaine to CSF via arachnoid granules

  • Other problem, in the past, was patient complaints of back pain after large doses of > 25 ml of local anesthetic

  • Formulations contained EDTA, thought that it “leached” calcium out of the muscle and resulted in hypocalcemia.

  • The preservative free formulations do not appear to cause back pain after large doses have been used


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Short Acting 2-chloroprocaine to CSF via arachnoid granules

  • Best suited for short procedures

  • Good agent for the outpatient

  • Available in concentrations of 2% (for procedures that do not require absolute muscle relaxation) and 3% which provides for dense muscle relaxation.

  • 2-chloroprocaine will interfere with the action of epidurally administered opioids


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Short Acting 2-chloroprocaine to CSF via arachnoid granules


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Intermediate Acting Lidocaine to CSF via arachnoid granules

  • Prototypical amide local anesthetic

  • 1.5-2% concentrations used for surgical anesthesia

  • Epinephrine will prolong the duration of action by 50%

  • Addition of fentanyl will accelerate the onset of analgesia and create a more potent/complete block


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Intermediate Acting Lidocaine to CSF via arachnoid granules


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Intermediate Acting Mepivacaine to CSF via arachnoid granules

  • Similar to lidocaine

  • Amide local anesthetic used in similar concentrations

  • Lasts about 15-30 minutes longer than lidocaine

  • Epinephrine will prolong the duration of action by 50%


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Intermediate Acting Mepivacaine to CSF via arachnoid granules


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Long Acting Bupivacaine to CSF via arachnoid granules

  • Long acting amide local anesthetic

  • 0.5-0.75% concentrations used for surgical anesthesia

  • 0.125-.25% used for epidural analgesia

  • Epinephrine will prolong duration of action but not to the extent of lidocaine, mepivacaine, and 2-chloroprocaine


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Long Acting Bupivacaine to CSF via arachnoid granules

  • 0.75% concentration should not be used in OB

  • In 1983 the FDA came out with this recommendation

  • There were several cardiac arrests due to inadvertent intravascular injection in OB patients

  • Bupivacaine (as well as etidocaine) are more likely to impair the myocardium and conduction system with toxic doses than other local anesthetics


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Long Acting Bupivacaine to CSF via arachnoid granules

  • Bupivacaine has a high degree of protein binding and lipid solubility which accumulate in the cardiac conduction system and results in the advent of refractory reentrant arrhythmias


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Long Acting Bupivacaine to CSF via arachnoid granules


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Long Acting Levobupivacaine to CSF via arachnoid granules

  • S isomer of bupivacaine

  • Used in the same concentrations

  • Clinically acts just like bupivacaine with the exception that it is less cardiac toxic


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Long Acting Levobupivacaine to CSF via arachnoid granules


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Long Acting Ropivacaine to CSF via arachnoid granules

  • Long acting amide local anesthetic

  • Mepivacaine analogue

  • Used in concentrations of 0.5-1% for surgical anesthetic

  • Used in concentrations of 0.1-0.3% for analgesia

  • Ropivacaine is unique among local anesthetics since it exhibits a vasoconstrictive effect at clinically relevant doses


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Long Acting Ropivacaine to CSF via arachnoid granules

  • Similar to bupivacaine in onset, duration, and quality of anesthesia

  • Key differences include: in doses for analgesia there is excellent sensory blockade with low motor blockade and it is less cardiotoxic than bupivacaine


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Long Acting Ropivacaine to CSF via arachnoid granules


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Long Acting Etidocaine to CSF via arachnoid granules

  • Long acting amide local anesthetic

  • Not used clinically very often due to the profound motor blockade it induces

  • When used for surgical anesthesia it is used in a concentration of 1%


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Long Acting Etidocaine to CSF via arachnoid granules


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Epidural Additives to CSF via arachnoid granules

  • Epinephrine will increase the duration of action of all epidurally administered local anesthetics.

  • There is a large variability among local anesthetics as to the degree of increase

  • The greatest effect is found with lidocaine, mepivacaine, 2-chloroprocaine.

  • Lesser effects found with bupivacaine, levobupivacaine, etidocaine

  • Minimal effects have been found with ropivacaine


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Epidural Additives to CSF via arachnoid granules

  • Epi vs phenylephrine

  • Epi is more effective in reducing peak blood levels

  • Phenylephrine does not appear to reduce the peak blood levels


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Epidural Additives to CSF via arachnoid granules

  • Carbonation of local anesthetics has been touted to improve the quality of epidural blocks due to increased penetration of connective tissue and intraneural diffusion

  • Studies are ambivalent

  • Carbonation may not improve quality or onset; may lead to increased blood levels of local anesthetic; result in a higher incidence of hypotension when compared to non carbonated local anesthetics


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Epidural Additives to CSF via arachnoid granules

  • Sodium bicarbonate can be added to lidocaine, mepivacaine, and 2-chloroprocaine

  • Addition will increase the amount of free base which increases rate of diffusion and speeds onset

  • Studies have found that when added to 1.5% lidocaine speeds onset of blockade and results in a more solid block


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Epidural Additives to CSF via arachnoid granules

  • Generally 1 meq of bicarbonate is added to 10 ml of local anesthetic (i.e. lidocaine, mepivacaine, 2-chloroprocaine)

  • The addition of bicarbonate to bupivacaine is not as popular. Usually 0.1 ml of bicarbonate is added to 10 ml of bupivacaine

  • Bupivacaine precipitates occurs at a pH > 6.8


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Epidural Additives to CSF via arachnoid granules

  • Mixing long acting and short acting local anesthetics may not have much advantage for epidural anesthesia

  • Many choices for local anesthetics and additives


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References to CSF via arachnoid granules

  • Brown, D.L. (2005). Spinal, epidural, and caudal anesthesia. In R.D. Miller Miller’s Anesthesia, 6th edition. Philadelphia: Elsevier Churchill Livingstone.

  • Burkard J, Lee Olson R., Vacchiano CA. Regional Anesthesia. In Nurse Anesthesia 3rd edition. Nagelhout, JJ & Zaglaniczny KL ed. Pages 977-1030.

  • Kleinman, W. & Mikhail, M. (2006). Spinal, epidural, & caudal blocks. In G.E. Morgan et al Clinical Anesthesiology, 4th edition. New York: Lange Medical Books.

  • Niemi, G., Breivik, H. (2002). Epinephrine markedly improves thoracic epidural analgesia produced by small-dose infusion of ropivacaine, fentanyl, and epinephrine after major thoracic or abdominal surgery: a randomized, double-blind crossover study with and without epinephrine. Anesthesia and Analgesia, 94, 1598-1605.

  • Reese CA. Clinical Techniques of Regional Anesthesia: Spinal and Epidural Blocks. 3rd edition. AANA Publishing, 2007.

  • Visser L. Epidural Anaesthesia. Update in Anaesthesia. Issue 13, Article 11. 2001.

  • Warren, D.T. & Liu, S.S. (2008). Neuraxial Anesthesia. In D.E. Longnecker et al (eds) Anesthesiology. New York: McGraw-Hill Medical.


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