neuraxial final

Spinal and Epidural Anesthesia

Jedarlyn G. Erardo, RPh, MD

Topic OutlineAnatomy

Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose

Combined Spinal-Epidural

Caudal Anesthesia

Complications

Spinal or Epidural Anesthesia

Anatomy

Surface Anatomy

• spine of C7 - first prominent spinous process in back of neck

• spine of T1 - most prominent spinous process and immediately follows C7.

• 12th thoracic vertebra can be identified by palpating the 12th rib and tracing it back to its attachment to T12

• A line drawn between the iliac crests crosses the body of L5 or the 4-5 interspace.

Ligaments•Supraspinous ligament•Ligamentum nuchae•Interspinous ligament•Anterior and posterior ligaments•ligamentum flavum

•thickest in the midline •farthest from the spinal meninges in the midline

Epidural space

• b/w the spinal meninges and the sides of the vertebral canal.• Cranial: foramen magnum• Caudal: sacrococcygeal

ligament (sacral hiatus)• Posteriorly: ligamentum flavum

and vertebral pedicles• discontinuous compartments -

opened up by injection of air or liquid

Epidural Fat

• w/ clinically important effects on the epidurally and intrathecally administered drugs.

• increasing lipid solubility resulted in opioid “sequestration” → reducing the bioavailability of drug

Meninges

• Dura mater• outermost and thickest• begins at the foramen magnum

forming the cephalad border of the epidural space.

• Caudally, it ends at approximately S2

• Plica medianis dorsalis• responsible for difficulty in

inserting epidural catheters and for unilateral epidural block.

• Subdural space. • Occasionally a drug intended

for either the epidural space or the subarachnoid space is injected here

• Arachnoid Mater • vascular membrane• principal physiologic barrier for

drugs moving between the epidural space and the spinal cord

• Subarachnoid Space• between the arachnoid mater

and the pia mater• contains the CSF

• in continuity with the cranial CSF and provides an avenue for drugs in the spinal CSF to reach the brain

• Contains the spinal nerve roots and rootlets

• pia mater• adherent to the spinal cord

In the adult, the caudad tip of the spinal cord typically lies at the level of the first lumbar vertebra.

The spinal cord gives rise to 31 pairs of spinal nerves, each composed of an anterior motor root and a posterior sensory root.

The skin area innervated by a given spinal nerve and its corresponding cord segment is called a dermatome

• preganglionic sympathetic neurons• Located in the intermediolateral gray

matter of the T1 through L2 spinal cord segments

• run with the corresponding spinal nerve to a point just beyond the intervertebral foramen where they exit to join the sympathetic chain ganglia.

• spinal cord ends between L1 and L2, the thoracic, lumbar, and sacral nerve roots run increasingly longer distances in the subarachnoid space to get from their spinal cord segment of origin to the intervertebral foramen through which they exit.

• cauda equina• nerves that extend beyond the end of

the spinal cord to their exit site


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


• Onset • Within few minutes regardless of the

drug used• Time to reach peak block is different

• Any procedure that can be performed under spinal can also be performed under epidural and requires same block height

Factors that may influence the spread of local anesthetics in the epidural space

• Injection site• Segmental block

• Drug volume and dose• ↑ volume ~ greater spread and density

• Drug concentration• Position • Age

• ↑ in elderly (less compliant epidural space and ↓ ability of LA to escape via intervertebral foramina)

• Height and weight

Onset

• Detected within 5 minutes• Peak effect

• Short acting 15 to 20 minutes• Long acting 20-25 minutes

• ↑ dose – speeds onset of motor and sensory block

• Block height• Baricity and patient position

• Onset• duration


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


• Site of Action• Can occur at any or all points along the

neural pathways extending from the site of drug administration to the interior of spinal cord

• Differential neural block• SNS nerve fibers appear to be blocked

by the lowest concentration followed by fibers responsible for pain, touch, and motor function

• SNS>Sensory>Motor

• Differential block is manifest as a spatial separation in the modalities blocked (sympathetic block may extend 2-6 dermatomes higher than sensory block, which is 2-3 dermatomes higher than motor block)

• Result from gradual decrease in local anesthetic concentration within the CSF as a fxn of distance from the site of injection

• Central neuraxial block produces sedation, potentiates sedative drugs and markedly decreases anesthetic requirements

Cardiovascular

• Blockade of SNS efferent fibers is the principal mechanism by which spinal anesthesia produces cardiovascular derangements• Incidence of significant hypotension or

bradycardia is generally related to the extent of SNS blockade, which in turn parallels block height

• Hypotension is the result of arterial (↓ SVR) and venous (↓ preload responsible for decreased CO) dilation

Fig 25-7

• HR slows significantly in 10-15% of patients (blockade of sympathetic cardioaccelerator fibers or diminished venous return and assoc decreased stretch of intracardiac stretch receptors)

• Can also produce 2nd and 3rd degree heart block.

Treating Hemodynamic Changes• Ephedrine boluses of 5 to 10 mg increase blood

pressure by restoring cardiac output and peripheral vascular resistance.

• Dopamine may be preferable to ephedrine for long-term infusion because tachyphylaxis can develop to repeated ephedrine boluses.

• Phenylephrine(increase BP by increasing SVR, w/c may decrease CO, may be specific tx for hypotension during epidural anesthesia provided by epinephrine containing local anesthetic solutions)

• Prehydrating patients with 500 to 1,500 mL of crystalloid does not reliably prevent hypotension.

• 500 mL 6% hetastarch may be an alternative to crystallloids

Respiratory

• Spinal and epidural blocks to midthoracic levels have little effect on pulmonary function in patients without preexisting lung disease.

• The negative impact of high blocks on active exhalation suggests caution when using spinal or epidural anesthesia in patients with obstructive pulmonary disease who may rely on their accessory muscles of respiration to maintain adequate ventilation.

• Patients with high spinal or epidural blocks may complain of dyspnea despite normal or elevated minute ventilation. (inability to feel the chest wall move while breathing adequately treated by reassurance)

• A normal speaking voice, as opposed to a faint gasping voice, suggests ventilation is normal.

GI

• secretions increase, sphincters relax, and the bowel becomes constricted

• Nausea is a common complication of spinal and epidural anesthesia• associated with blocks higher than T5,

hypotension, opioid premedication, and a history of motion sickness

Endocrine-metabolic

• spinal and epidural anesthesia have been shown to inhibit many of the endocrine–metabolic changes associated with the stress response• result from blockade of the afferent

sensory information that helps initiate the stress response


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Absolute

• Patient refusal• Coagulopathy• Infection at site• Hypovolemia/Septic shock• Increased ICP• Allergy to amides/esters

Relative

• Infection at site remote from injection• Viral infections

• (Herpes, Varicella, HIV)• Pre-existing CNS disease

• (MS, NTD)• Antiplatelet/anticoagulant drugs

• (ASA, NSAIDS, COX-2, Plavix, Warfarin, Heparin,LMWH)

• Decrased Platelet counts• < 100,000


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


• The outside diameter of both epidural and spinal needles is used to determine their gauge.

• Larger gauge (i.e., smaller diameter) spinal needles are less likely to cause postdural puncture headaches (PDPH), but are more readily deflected than smaller gauge needles.

• Epidural needles are typically sized 16 to 19 gauge and spinal needles 22 to 29 gauge.

Sedation

• Generally, the patient should not be heavily sedated because

• successful spinal and epidural anesthesia requires patient participation to maintain good position,

• evaluate block height, and

• indicate to the anesthesiologist about paresthesias if the needle contacts neural elements.

• Once the block is placed and adequate block height assured, the patient can be sedated as deemed appropriate


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Position

• sitting• often easier to identify the midline in

obese patients• allows one to restrict spinal block to the

sacral dermatomes• prone jackknife position

• Consider when surgery is to be performed in this position

• Hypobaric solutions produces sacral block for perirectal surgery.

• lateral decubitus

• patient lies with the operative side down when using hyperbaric local anesthetic solutions

• patient's shoulders and hips are both positioned perpendicular to the bed (prevent rotation of the spine)

• knees are drawn to the chest, the neck is flexed, and the patient is instructed to actively curve the back outward (spread the spinous processes apart and maximize the size of the interlaminar foramen)

• Remove jewelry/watches• Wash hands!• IV Access/fluid bolus if needed• Emergency drugs/equipment• Positioning• Sedation• Monitoring• NIBP/SPO2/ECG• Verbal contact with patient

• Using the iliac crests as a landmark, the L2–3, L3–4, and L4–5 interspaces are identified and the desired interspace chosen for needle insertion

• All antiseptic solutions are neurotoxic, and care must be taken not to contaminate spinal needles or local anesthetics with the prep solution.

Midline• subcutaneous tissue

• supraspinous ligament

• interspinous ligament

• ligamentum flavum

• epidural space

• dura mater

• arachnoid mater.

Paramedian

• inability to flex the spine or heavily calcified interspinous ligaments needle is inserted

~1 cm lateral to this point and is directed toward the middle of the interspace by angling it ~45 degrees cephalad with just enough medial angulation (~15 degrees) to compensate for the lateral insertion point.

Lumbosacral (or Taylor) approach

• paramedian approach directed at the L5-S1 interspace


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Continuous spinal anesthesia

• similar to “single shot” spinal anesthesia except that a needle large enough to accommodate the desired catheter

• After inserting the needle and obtaining free-flowing CSF, the catheter is simply threaded into the subarachnoid space a distance of 2 to 3 cm.

• Although smaller catheters decrease the risk of PDPH, they have also been associated with multiple reports of neurologic injury, specifically, cauda equina syndrome


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Hand-positionNote depthAir or Saline debateCatheter 3-5 cm in space (should go easily)

Loss of Resistance

Air vs Saline LOR Technique

Hanging drop technique


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Continuous Epidural Anesthesia

• greater flexibility • prolong a block that is too short, • extend a block that is too low, • provide postoperative analgesia.

• catheters may migrate • into an epidural vein, • into the subarachnoid space, • or out an intervertebral foramen.

• more likely to result in unilateral epidural block

• through either Tuohy or Hustead needles

• (+) resistance as it reaches the curve at the tip of the needle, • steady pressure will result in passage

into the epidural space.

advance only 3 to 5 cm into the epidural space.


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Epidural test dose

• must be administered before incrementally delivering the entire epidural drug dose.

• risk of undetected iv or subarachnoid migration of the catheter over time, additional test doses must be administered before each top-up dose

• reasonable guideline for top-up doses • half the initial local anesthetic dose at

an interval equal to two thirds the expected duration of the block.

Epidural test dose

• Aspirating the catheter or needle to check for blood or CSF • false negative aspirations is too high

• 3 mL of local anesthetic + 5 mg/mL epinephrine (1:200,000). • subarachnoid injection of LA→ spinal

anesthesia. • Intravenous injection of epinephrine →

average 30 beats per (20 and 40 seconds)


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Combined spinal epidural anesthesia

rapid onset, dense block of spinal anesthesia

+

flexibility afforded by an epidural catheter.

volume effect (compression of the spinal meninges forcing CSF cephalad)

• potential risk • meningeal hole made by the spinal

needle may reach the subarachnoid space


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


1. Backache

• Spinal (11%)• Epidural (30%)• Needle trauma, local anesthetic

irritation, ligamentous strain 2° to muscle relaxation

2. Postdural puncture headache

• mild or absent when supine but head elevation results in fronto occipital headache

• cranial nerve symptoms (diplopia and tinnitus and nausea and vomiting)

• loss of CSF thru the meningeal needle hole resulting in decreased buoyant support for the brain

• In the upright position, the brain sags in the cranial vault, putting traction on pain-sensitive structures and possibly cranial nerves

• decreases with • increasing age• use of small diameter spinal needles with

non cutting tips• Use of fluid than air for determining loss of

resistance• Inserting cutting needles with the bevel aligns

parallel to the long axis of the meninges results in a meningeal opening that is likely to be pulled closed by the longitudinal tension present on the dura mater

• Resolves spontaneously in a few days with conservative therapy (bed rest, analgesics, and caffeine)

• Epidural blood patch (10-20 mL of autologous blood) • relief in 85 to 95% of patients within 1 to

24 hours• Epidural administered fibrin glue

• 3. Hearing loss (transient, lasting 1 to 3 days)

• 4. Systemic toxicity (CNS and cardiovascular toxicity )• Intravascular absorption or accidental

IV injection• Adequate test dose and incremental

injection

5. Total spinal

• entire spinal cord and occasionally the brainstem

• Profound hypotension and bradycardia (sympathetic blockade)

• Apnea (respiratory muscle dysfunction or depression of brainstem control cneters

• Vasopressors, atropine, fluids and oxygen Plus controlled ventilation of the lungs (if managed appropriately will resolve without sequelae)

6. Neurologic injury

• 0.03 to 0.1% • Most common – persistent paresthesia

and limited motor weakness• Hyperbaric 5% lidocaine

• cauda equina syndrome ffg subarachnoid injection thru small bore (high resistance) catheters during continuous spinal anesthesia

• little turbulence and undiluted local anesthetic pool around dependent cauda equina nerve roots

• 7. Transient neurologic symptoms (TNS)• Pain and or dysesthesia in the buttocks

or legs ffg spinal anesthesia (greater with lidocaine regardless of the dose)

• Sx in the lithotomy position and obesity may increase the risk

• resolves in 72 hours• Chloroprocaine

• Preservative free • not associated with TNS

8. Spinal hematoma

• Rare (<1 in 150 000) • lower extremity numbness or weakness• critical time: within 8 hours• Coagulation defects


Pharmacology

Physiology

Contraindications

Technique

Spinal Anesthesia

Continuous Spinal

Epidural

Continuous Epidural

Epidural Test Dose


Caudal Anesthesia

Complications


Spinal Anesthesia

• Less time to perform• More rapid onset• Better quality sensory and motor block• Less pain during surgery

Epidural Anesthesia

• Less risk of post dural puncture headache• Less hypotension if epinephrine is not

added to local anesthetic solution• Ability to prolong or extend block via an

indwelling catheter• Option of using an epidural catheter to

provide post operative analgesia

THANK YOU!

neuraxial final

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