Neuraxial Flashcards
5 different types of central neuraxial techniques
Subarachnoid: -Spinal -Intrathecal -Spinal Anesthetic Block (SAB) Epidural -Epidural -Caudal
Spine vertebrae (different sections, how many per section)
Cervical: 7
Thoracic: 12
Lumbar: 5
Sacral: 5
Vertebrae components
Vertebral body Pedicles (2) Transverse Processes (2) Laminae (2) Spinous process Articular processes (4) -Superior (2) vs Inferior (2) -Stack to make the intervertebral foramina
Spinous processes at cervical/thoracic level vs lumbar
Cervical/Thoracic: -Angles in caudal direction, overlap -Need to adjust needle angulation to access epidural space Lumbar -Easier to access -Less acute angle, more open space
Spinal cord (adult) terminates at ____
L1-L2
- Important for spinal technique, need to enter below this level so you don’t injure the cord
- Epidural doesn’t necessarily follow this since you don’t (aren’t supposed to) enter this space
Ligaments supporting the spinal cord
Supraspinous -Joins the apexes of the spine of the vertebrae -Major ligament in cervical and thoracic spine Interspinous -Joins spinous processes -Very thin Flavum -3-5mm thick -Helps maintain posture -Yellow color -Right before epidural space
Meninges (3 different layers and characteristics)
3 membranes: Dura -Outermost layer, thick -Most of the protection of the CNS -Feels like popping through a water balloon Arachnoid -Thin -Very close to the dura matter in the back (minimal subdural space) -Subarachnoid space is under this Pia -Thin -Directly covers the spinal cord
Epidural space
- Runs entire length of the spine
- Segmented and interconnected
- Contains: Blood vessels, fat, lymphatics, nerve roots
- Typical distance from skin->epidural space in adults = 5-8cm
- Average lumbar AP distance = 5mm
Spinal blood supply
Anterior spinal artery -2/3 of anterior cord -originates from vertebral artery Posterior spinal arteries (2) -1/2 of posterior cord -originates from cerebellar arteries Segmental spinal arteries -artery of Adamkiewicz: anterior lower 2/3 of cord Veins: Spinal veins (3 anterior, 3 posterior) communicate with epidural veins
Cerebral Spinal Fluid (characteristics, where it’s produced, how much is produced, specific gravity)
Characteristics -Clear -Occupies subarachnoid space -Acts as a cushion and shock absorber Produced in choroid plexus -500mL/day Specific gravity: 1.004-1.009 -Affect drug choice
Surgical types appropriate for neuraxial anesthesia
General surgery (below bellybutton)
Urology procedures
Rectal procedures
Lower extremity procedures
Pros of neuraxial anesthesia
Narcotic sparing Blunted stress response Decreased blood loss (tourniquet use) Can do cases awake (C-section, TURP) -Safer for less optimized patients Less overall med usage (less N/V, alert) Avoid airway manipulation, meds associated with it
3 absolute contraindications for neuraxial anesthesia
Patient refusal/inability to cooperate
Localized sepsis (in area needle will enter)
Increased ICP
Relative contraindications for neuraxial anesthesia
Previous spine surgery
-Variable block d/t epidural space violation (rather than contraindicated because of complications)
-Ligaments aren’t there for landmarks
Evidence for other neurological issues aren’t rooted in evidence
-Back pain, spinal stenosis, MS
-Spina bifida: Increased risk of damage to neurological structures
Aortic stenosis
-D/t decreased afterload from vasodilation -> cardiac/circulatory arrest
Hypovolemia
Thromboprophylaxis
Coagulopathies
-Plt<100,000
-PT or aPTT 2x normal value
Infection
-OK if afebrile and being treated
Differential blockade
When transmission is altered in one type of nerve fiber but not another
- Sympathetic=always the first to go/spreads out to the furthest dermatomes. 2 above sensory
- Sensory=2 above motor
- Motor
Myelination and Function of A-a, A-B, A-d, B, and C fibers
A-a: Heavy myelination, Motor
A-B: Moderate myelination, Touch/Pressure
A-d: Light myelination, Pain/Temperature
B: Light myelination, Preganglionic Autonomic
C: No myelination, Pain/Temperature
Mechanism of Action of blockade (Primary and secondary)
Bind to Na channel in inactive state, stop potentiation
Primary: Spinal roots
Secondary: Spinal cord, brain
Factors that affect the level of blockade
Patient position Baricity of drug Drug dose/volume Site of injection Others -Age -Spinal issues -Intra-abdominal pressure (pregnant, spinal column Is smaller/compressed -> less meds will spread more) -Injection pressure
Baricity (CSF SG, ratios of hyper/hypo/iso)
How LA is compared to the CSF (ratio of LA SG: CSF SG)
-Resting position of 2 fluids with different specific gravities when they’re mixed
CSF SG: 1.004-1.009
Hyperbaric: SG>1.015
-Add dextrose
-Drug sinks to gravity
Isobaric: SG=1
-Add NS or CSF
-Use for hip cases so when they lay on their side both LEs stay numb
Hypobaric: SG<0.999
-Add sterile water (not really used in practice)
Factors you can control that contribute to the pharmacological spread
Total dose of drug
Site of injection
Baricity of drug
Patient position after injection
Cardiovascular effects of neuraxial block
Arterial dilation
Decreased SVR
Increased venous pooling
Decreased preload
Where sympathetic fibers arise from vs sympathetic cardio accelerator fibers
Sympathetic fibers: T5-L1 (vasomotor tone)
Sympathetic cardio accelerator fibers: T1-T4
-Unopposed vagal tone -> Bradycardia/Asystole
Treatment for cardiovascular effects after neuraxial block
IVF to increased preload -Colloid vs crystalloid is controversial Alpha/Beta agonists 5-HT3 antagonists Atropine if it's a high spinal
Pulmonary effects of neuraxial block
Loss of accessory muscles Loss of perception of breathing Small decreased in VC Phrenic nerve impairment if total spinal (C3-C5) Impaired cough
GI effects of neuraxial block
Unopposed vagal tone
Increased peristalsis
Relaxed sphincters
Miscellaneous effects of neuraxial block
Decreased thermoregulation
Decreased stress response
Immediate complications of neuraxial block
Total spinal -If epidural volume is injected into spinal space (20mL vs 3mL), avoid with test dose Cardiac arrest Failed spinal GI complications IV injection/LAST
Complications of total spinal block
Rapid onset, ascends into cervical levels
-Restless, hypotensive, bradycardic, apneic
Complications of IV injection/LAST
Restless, seizures, coma, cardiac collapse
-Follow LAST protocol
How to avoid IV injection during neuraxial block
Always aspirate on epidural catheter before injecting (blood if intravascular, although slow; CSF if past dura)
Give test dose after placing an epidural catheter
How to do test dose on epidural catheter, what to watch for
- 3-5mL 1.5% lidocaine with 1:200,000 Epi
- Rules out intrathecal placement: Would get numbness in toes within 10 seconds if it was spinal
- Rules out intravascular placement: Would see 15% increase in baseline HR because of Epi
4 potential places epidural catheters could be
Epidural space
Epidural space: In blood vessel
Intrathecal/Subarachnoid space (wet tap)
Flavum (can’t thread catheter)
Overall complications to tell patients before neuraxial block
Post dural puncture headache (PDPH) Urinary retention Backache Transient neurological symptoms (TNS) Caudal equina syndrome Nerve injury
Post dural puncture headache (PDPH) factors, mechanism, symptoms, treatment
Factors
-Needle guage (spinal needles=smaller, 24-29g, less likely 1/100 vs epidural needles 17-18g, more likely 60-80%)
-Cutting (more likely) vs pencil tip
-Bevel direction (parallel to dural fibers minimize risk)
Mechanism
-Decrease in CSF -> brain/brainstem drops into the foramen magnum -> tug on meninges
-Possibly vasodilatory mechanisms from lack of CSF
Symptoms
-Light sensitivity
-Postural headache (have to lay flat, less pressure on brainstem dropping)
-Nausea/Vomiting
Treatment
-Gold standard: Blood patch
-Sphenopalatine ganglion block
-Fluid, caffeine, rest
Neurological injury from neuraxial blocks
Rare, subdural or epidural hematoma
-Can usually rule out patients who this could happen to during preop interview (bruising/bleeding questions, thrombophylaxis, thrombocytopenia)
Causes
-Needle trauma, surgical trauma, positional
-Chemical (drug), virus, bacteria
-Ischemia
*Devastating effect, can lead to paralysis
*Neuro checks, referral for rapid decompression if needed (goal=<8 hours after symptoms present)
Cauda equina syndrome (Symptoms, cause)
Persistent paralysis of nerves of cauda equina -> LE weakness, bowel/bladder dysfunction
Associated with microcatheters, small needles, repeat dosing, hyperbaric local anesthetics (5% lidocaine)
-Repeat spinal dosing=risky
-FDA removed small needles and microcatheters in 1992
Transient neurological syndrome
Symptoms -Pain in buttocks/LEs -Bowel/bladder dysfunction Risk -5% Lidocaine (Other anesthetics have been implicated but it'll much more prevalent after spinal lidocaine) -Chloroprocaine (when it used to have preservatives) Treatment -Usually resolves on its own -Can give NSAIDs
Infection after neuraxial block (2 types, treatment, prevention)
Meningitis -Contaminated equipment -Glass particles -Coring of tissue Epidural abscess -Back pain with fever Treatment -Antibiotics, surgical decompression Prevention -Sterile field, remove catheters after 96 hours
Spinal needles
All have stylets to avoid coring Quinke -Standard cutting -22-25g Spotte, pencan, Whitacre -Non cutting, pencil tip -Different side port shapes -22-29g (smaller 24-29 need introducer needle
Difference between cutting and pencil tip needles
If name has “K” sound in it it’s most likely a cutting needle
- Cutting needles can pierce a cauda equina root without knowing (damage nerve)
- Cutting needles give less perceptive feedback
- PDPH is 3x higher when using a cutting needle vs pencil tip
- Cutting needles can deviate
Epidural needles, catheters
Needles -Have a curve on the end to thread catheter -17-19g -Touhy, Crawford, Weiss Catheters -Single or multiple orifices -Wire reinforced -Usually 2g smaller than needle
How far to advance epidural catheter
3-5cm past how many cm it took to get to epidural space/loss of resistance
Sitting vs side lying positioning
Sitting
- Easier to achieve interspinous space
- Easier to assess midline
- Easier to assess landmarks
- Patients need to “round out” their back
Tuffier’s Line
Top of iliac crests, intersects with spine at ~L4
Bromage grip
How to anchor needle when placing spinal
- Nondominant hand grasps needle hub between pointer and thumb
- Back of hand/fingers brace against patients back to stabilize your access point
What type of LA/what needle to use before spinal/epidural technique
10-20% lidocaine
25g needle
Paramedian approach
~1’’ off midline ~15 degree approach
- Avoid in horizontal anatomy
- Use if you can’t get good space between vertebrae with rounding back out
Drugs for spinal (LA, opioids, adjunts)
LA -Bupivacaine -Tetracaine -Chloroprocaine Opioids -Morphine -Fentanyl -Dilaudid Adjunts -Vasoconstrictors -Alpha-2 agonists *Everything needs to be preservative free
Bupivacaine for spinal
- 75% in dextrose (1.6-2mL)
- Hyperbaric
- Gives dense block up to T4
- Good for longer procedures (3 hours) - 5% (2.5-3mL)
- Isobaric
- Good for lateral procedures (hip) since won’t sink
- Same DOA and block density as .75%
Chloroprocaine for spinal
2-3% 2-2.5mL
Lasts 1-1.5 hours
-Good for outpatient surgery
Opioids for spinal
*Preservative free Morphine ->200mcg=little analgesic benefit with increased SE -Pruritis, N/V Dilaudid -70-100mcg -Less pruritic/N/V Fentanyl -25mcg
Vasoconstrictors in spinal
Epi
- 1:1000, 0.1-0.2mL (~100mcg)
- Do “Epi wash”=Aspirate 1mL into syringe and then squirt it out, use same syringe to draw up LA
Alpha 2 agonist in spinal
Precedex can prolong the duration of the block
Epidural volume, how to determine density and level
2mL/level
Density=concentration
Level=volume
-Max spread occurs after 15-25 minutes
Bupivacaine in epidural
- 5% for surgical anesthesia (careful, can get close to toxic doses/2.5-3mg/kg)
- 25% for analgesia (not anesthetic dose)
- 125% for sensory>motor block (postop pain relief)
Opioids in epidurals
Fentanyl 50-100mcg bolus Morphine 3mg (>3=high risk of respiratory depression)
OB epidural
- 2% Ropivacaine with 2mcg/mL fentanyl
- 8-10mL/hr
- 4mL bolus q30min (PCA)
Ropivacaine in epidurals
- 2%
- Analgesic block
Spinal vs epidural onset, duration, density
Onset -Spinal=quick -Epidural=variable Duration -Spinal=set -Epidural=variable Density -Spinal=set -Epidural=variable *Epidurals are customizable vs spinals-once injected they're done
Combined spinal epidural (advantages, disadvantages, approaches)
Advantages -Quick onset -Prolonged duration -Confirms needle is in epidural space Disadvantage -Can mask a patchy epidural for ~2hours Approaches -2 level (epidural normal, spinal 1 level down) -Needle through needle -Specialized combined CSE needles
Caudal anesthesia
Used in peds d/t ease of access
Position: Prone, lateral
-Palpate cornua of sacral hiatus
-Needle advanced at steep angle between cornua
-Popping sensation when entering sacral ventral canal
-Needle angle lowered to parallel sacrum/spinal canal, advanced 1-3cm
-Medication injected or catheter placed by catheter over needle technique
0.5-1mL will achieve umbilicus level coverage
How is the sympathetic blockade level judged
Temperature sensitivity
Neuraxial anesthesia doesn’t block ____ nerve
X: Vagus -> unopposed parasympathetic tone
For spinal anesthesia what order are spinal nerves anesthetized in
1: Pre-ganglionic sympathetic
2: Temperature
3: Pinprick
4: Touch
5: Motor
Dermatome level for thoracic/upper abdominal/mid abdominal/lower abdominal/lower extremity epidural placement
Thoracic: T4-8 Upper abdominal: T6-8 Middle abdominal: T7-10 Lower abdominal: T8-11 Lower extremity: L1-L4
