The spinal canal runs from the ____ _____ to the _____ _____.
Where does the spinal cord begin?
At the medulla oblongata
Where does the spinal cord end?
L1-2 conus medullaris->cauda equina
What is the primary site for neuraxial anesthesia?
The lumbar vertebral column
Describe the bony anatomy of the vertebrae
Anterior-vertebral body, disc
Posterior-ring containing the spinal cord-body, fascicles, laminae
What attaches to laminae superiorly & inferiorly?
What is found in the epidural space?
Epidural fat, blood vessels (epidural veins), nerve roots (spinal nerves)
Describe the dura mater
Outer most layer covering the spinal cord
What is the dura mater attached to?
Attached superiorly to the foramen magnum
Where does the dura mater end?
Inferiorly it ends at the S1-S2 vertebra
What covers spinal nerves?
Where do the spinal nerves exit?
Via the intervertebral foramina (in pedicles)
Where do spinal nerves enter?
The paravertebral space
The meninges consist of 3 layers, name them.
Dura mater, arachnoid mater, pia mater
The sympathetic are part of the _______ system.
Describe the thoracolumbar system
Sympathetic nerve fibers run thru the intermediolateral cell column of T1-L2 & consist of preganglionic beta fibers.
What vertebral levels are the cardiac accelerators?
Efferents at every level contribute to ____ ____->sympathectomy causes _______ in proportion to the ______ of ______ blocked.
# of dermatomes blocked
What are the 4 major structural ligaments of the spinal column?
Posterior to anterior
Posterior longitudinal ligament
Anterior longitudinal ligament
What does spinal cord consist of?
An outer white matter & middle gray matter
What does the gray matter consist of
Shaped like a butterfly
Consists of anterior, lateral, & dorsal horns
Sympathetics exit via ____ ____ and then enter into the ____ _____ ____.
lateral sympathetic chain
Explain sympathetically mediated pain?
Afferents (sensory) = activated by stretching, ischemia, and inflammation
How do the afferent nerves affect the SNS?
Activated by stretching, ischemia, & inflammation
What is the only parasympathetic nerve that innervates the heart?
What parasympathetic nerves are affected by epidural blockade?
Only sacral S2-4 (When knocked out, this causes urinary retention)
What parasympathetic nerves are not affected by epidural blockade?
Cranial nerves (III-oculomotor, VII-Facial, IV-glossopharyngeal, X-Vagus, XI-accessory)
Spinal or epidural above _______ leads to increased risk of trauma to spinal cord.
Must go below
Why is it safer to place a spinal or epidural below L1-2?
Cauda equina nerves freely float in CSF = not easily traumatized
Why is the lumbar epidural the most commonly performed block?
Easiest approach d/t near horizontal spinous processes, ligamentum flavum thick in comparison to thoracic, bigger interspaces
What disease process causes difficulty in regards to a lumbar epidural?
What is the most common injection site in a lumbar epidural and why?
How do spinal nerves that come off the spinal cord innervate the body?
In a dermatomal fashion
What do dermatomes correspond with?
The level at which the nerves exit the spinal cord, they don't correspond w/ peripheral nerves
In regards to dermatomes blocking what level leads to hand numbness?
C6, 7, 8
In regards to dermatomes what level affects below the clavicle?
In regards to dermatomes what level affects the nipple line?
In regards to dermatomes what level affects the xiphoid process?
In regards to dermatomes what level affects the umbilical level?
In regards to dermatomes what level affects the ilio-inguinal level?
In regards to dermatomes what level affects the pubic rectal area?
At what level do spinous process meet their maximal angulation?
T7 (60˚ angle)
Where is the site of action of epidurals & why is this important?
Spinal nerve roots, the LA has to cross all 3 layers of meninges = slower onset than spinals
What layer of meninges acts as a major barrier to diffusion in epidurals and what is its effects?
Arachnoid-epidurals set up slower than spinals
What is the mechanism of epidural blockade?
Spread of local in the epidural space (bidirectional spread)
Describe a differential blockade w/ epidurals.
Lower concentrations block sympathetic & sensory fibers while leaving proprioception & motor intact.
What are CV effects dependent on?
Dose & level obtained
At what level would adrenal afferents be knocked out and what is the effects?
T6-L1; increased vagal tone->blunts HR response
What factors cause a decrease in arterial pressure?
↓ peripheral resistance
↓ CO d/t ↓d venous return & T1-T5 blocked-> ↓d HR & contractility
↓ in central venous pressure d/t venodilation
What is the major factor causing a decrease in arterial pressure and why?
↓ CO d/t venodilation causing ↓ venous return
Also blocks T1-5
How does arterial vasodilation & ↓ BP affect limb blood flow?
Limb BF below the block is improved
Limb BF above the block is reduced
At what level are CV effects of neuraxial blockade at maximal level?
T1 (after T1 will result in profound bradycardia)
Arterial vasodilation but local compensation:
Only ____-____% ↓ total vascular resistance.
Mean arterial pressure only ↓ ___-____% even w/ high block provided CO maintained.
Venodilation may be maximal
There may be ____ ____ w/ changes in posture.
What do pooling effects lead to?
↓ preload & CO
What is CO determined by?
May be normal if ______ & _____ ____ _____ ____.
May be normal if normovolemia, & legs above heart level.
What happens to the HR w/ a T1-T4 block?
What happens to HR if RA pressure is decreased?
Decreases (usually ↓ 10-15% unless T1 block or ↓↓ RA pressure)
What is the key to preventing a decrease in HR?
If a patient c/o nausea what could be the cause and how should it be treated?
Describe how neuraxial blockade can effect the respiratory system.
Can block the phrenic nerve if C3C4 blockade ("high spinal").
Chest wall heaviness common - Intercostal muscles segmentally innervated - Lack of sensation (proprioception).
Describe how neuraxial blockade can effect the GI system.
Unopposed vagal tone-> ↑ in GI motility
↓ incidence of colonic anastomotic dehiscence d/t improved BF
What are the indications for epidural blockade?
Surgical anesthesia, relief of acute & chronic pain
What procedures are associated w/ acute pain and would be relieved w/ epidurals?
OB, post-op pain, fractured ribs, etc...
Epidurals block ____ & _____ at the level of the nerve root.
Afferents & efferents
How should an epidural be placed in order to minimize SE & maximize therapeutic effects?
Should be placed at the center of the dermatome providing the maximal stimulation. Epidurals provide segmental analgesia->spreads from a central area where they are placed then cephalic & caudal.
What are the advantages of epidurals in OB?
Sympathectomy early ↑ing UBF (if BP maintained)
Motor blockade can be minimized
Lower body only
2nd stage labor (S2-4) needs deeper block (need larger volume)
Easy to convert for c-section
Advantage in certain OB complications
↓ the BP on pre-eclamptic pts
What are the absolute contraindications for epidurals?
Hypovolemia, ↑d ICP, infection at site, septicemia, hypocoagulation states, patient refusal (assault), critical AS
Why is it contraindicated to perform an epidural on a pt w/ critical stenosis?
Restrict the ability of the ♥ to ↑ CO as compensation for hypotension d/t the sympathectomy induced by neuraxial anesthesia. In these circumstances, the hypotension can become refractory to tx.
What are the relative contraindications for epidurals?
Severe AS (need a-line)
Chiari malformation & cerebral aneurysms (risk occurs w/ wet tap)
Degenerative spine ds w/ neurologic findings (sciatica, foot drop, etc)
Unstable neurologic ds
Spine pathology (prior sx, severe scoliosis)
What is the most common approach for epidurals?
Lumbar midline approach-pt in upright or lateral position.
____ _____ is at L4 spinous process.
What level is the best place for epidurals?
What factors need to be considered in regards to lateral positioning in men & women, especially w/ spinals?
Women have larger hips->will cause hyperbaric LA to travel more cephalad
Men have broader shoulders->higher chance of inadequate spinal
What techniques are used in neuraxial anesthesia?
Paramedian lumbar & thoracic approach
Midline thoracic approach
Describe the paramedian approach
Bypasses the supraspinous & interspinous ligaments->resistance can be boggy until ligamentum flavum is engaged.
What is the purpose of a test dose?
To check for proper placement and that you do not have intrathecal or intravascular injections.
What drugs and dosages are used w/ epidural test doses?
1.5% lido w/ epi 1:200,000
3cc = 45mg lido + 15 µg epi
Allow enough time (sensory check)
Why should each dose of an epidural be treated as a test dose?
Catheters can migrate intrathecally after a negative test dose->need to aspirate & don't give big doses as a bolus = high spinal
What is the level of insertion for labor analgesia?
What is the level of insertion for hip/knee surgery?
What is the level of insertion for laparotomy under GA?
What is the level of insertion for a thoracotomy or fractured ribs?
At relevant interspace usually T5-T7
What is the MOA of duramorph?
↓ substance P mediated transmission from A-delta & C fibers by ↓ing presynaptic Ca influx & hyperpolarizing the 2nd order ascending nerve by ↑ing K conductance->suppresses expansion of nociceptive field of 2nd order neuron-> ↓s c-fos expression.
What is the DOA of duramorph?
What are the disadvantages of duramorph?
Can cause delayed respiratory depression up to 12˚
What are the differences between duramorph & lipid soluble opioids?
Duramorph spread more = > risk for CNS SE
What are the advantages of lipid soluble opioids?
Quick onset, low risk of respiratory depression (less dermatomal spread)
What are the disadvantages of lipid soluble opioids?
Short DOA, must be injected near the site of action (d/t less dermatomal spread), rapid systemic absorption
What are the S.E. of neuraxial opioids?
Respiratory depression (may be delayed 8-12˚), N&V, pruritis, urinary retention, ↓ GI motility (less than w/ IV)
Why does urinary retention occur w/ neuraxial opioids?
Due to inhibition of sacral parasympathetics
Describe why pruritis occurs w/ neuraxial opioids and how its treated.
Mu receptor, peripheral histamine release
Antihistamines have limited efficacy, narcotic agonist/antagonist best-naloxone
How does addition of epi affect neuraxial blockade?
Vasoconstriction-> ↓d uptake of LAs, prolongs block, ↓d spinal cord BF, intensifies motor block, direct α-2 mediated antinociceptive effects on 1˚ afferents & descending pathways.
How does addition of phenyephrine affect neuraxial blockade?
Vasoconstrictor->prolonged block, ↓d uptake
May ↑ risk of TNS
Describe effects of adjuvant clonidine & neuraxial blockade
Inhibit A-delta & C fiber afferents by ↑d K conductance
Rapid systemic absorption->peripheral inhibition of norepi release
Describe effects of adjuvant neostigmine & neuraxial blockade
Acetylcholinesterase inhibitor-> ↑ Ach, stimulates receptors in substantia gelatinosa
What is a disadvantage of neostigmine?
High incidence of nausea
Describe effects of adjuvant ketamine & neuraxial blockade?
Non-competitive NMDA antagonist-> ↓s central sensitization "wind up"
Describe effects of adjuvant ketorolac & neuraxial blockade?
COX inhibitor (NSAID)->under investigation, may enhance opioid & clonidine analgesia
What patients cannot be sedated prior to epidural blockade?
Between ephedrine & phenylephrine which is a better choice in treatment of hypotension & why?
Ephedrine best (↑ preload & CO)
Phenylephrine (↑ afterload)
Why is atropine a poor choice in the treatment of hypotension?
↑ HR & MVO2
What factors affect the spread of LAs in the epidural space?
Rapidity of dose (>), volume injected (>), placement of catheter, position, unique epidural anatomy (prior sx, spinal stenosis, pregnancy, ht)
Describe the difference in subarachnoid block vs epidural block.
Dura & arachnoid intentially punctured, smaller needle gauge, pencil point needles (less risk of PDPH), introducer needles used.
Why are introducer needles used w/ subarachnoid blocks?
Due to smaller needle gauge (25-27 ga), prevents skin "coring" & provides rigidity.
Where are spinals performed?
Below L2-3->spinals above L2-3 carry the additional risk of direct trauma to the cord (iatrogenic syringomyelia) or the posterior spinal artery.
With a subarachnoid block where is the drug deposited?
Into the CSF
How are spinals performed?
With a subarachnoid block what determines the level?
Baricity & positioning
Describe onset of the subarachnoid block
Rapid->LA doesn't have to diffuse across dura & arachnoid->rapid sympathectomy
What are the advantages of a subarachnoid block?
Lower dose of LA needed, slower absorption of LA
Both decrease risk of systemic toxicity
Where do subarachnoid blocks work?
Directly on nerve roots & spinal cord (Virchow-Robin spaces)
What factors affect the distribution of subarachnoid anesthetics?
Relative baricity of LA, position, volume inj, level where spinal was placed, rapidity of inj
How does the rapidity of the injection affect the subarachnoid block?
Provides good mixing w/ the CSF->causes turbulence
____ is duration. ____ determines the level.
Dose is duration
Positioning determines the level
Compare epidural vs spinal blockade
Covering the nerves-onset
Location of action
Differential blockade-more difficult w/ spinals
What dermatome level is necessary for upper abdominal surgery w/ a spinal?
What dermatome level is necessary for intercostal sx (including appy, gynecologic pelvic sx, & ureter & renal pelvic sx) w/ a spinal?
What dermatome level is necessary for a TURP, obstetric vaginal delivery, & hip sx w/ a spinal?
What dermatome level is necessary for TURP, if no bladder distention; thigh sx; lower limb amputations w/ a spinal?
L1 (inguinal ligament)
What dermatome level is necessary for foot surgery w/ a spinal?
L2-L3 (knee & below)
What dermatome level is necessary for perineal surgery, hemorrhoidectomy, anal dilation w/ a spinal?
When a spinal is done & the pt is laid completely flat where does the LA usually spread & why?
T4, it's a little above the bottom of the thoracic kyphosis (most dependent portion of the thoracic spine)
How is the epidural space identified?
With loss of resistance
How is a combined spinal-epidural performed?
Epidural space identified, subarachnoid block then performed by inserting a spinal needle thru the Touhy/modified Touhy, epidural catheter is then inserted via the Touhy
What are the advantages of a combined spinal-epidural?
Offers the advantages of rapid onset & dense block of a spinal & the flexibility of redosing via an epidural catheter.
After the subarachnoid block is performed, the epidural must be threaded & secured expeditiously so the pt may be positioned to allow proper spread of the subarachnoid LA, what would occur if the pt remained seated too long?
A saddle block would result
When dosing the epidural after spinal block, the epidural exerts a ____ ___ on the epidural space, this will push the spinal level _____ than expected for simple epidural dosing.
When dosing an epidural after a dural puncture, some local will leak thru the puncture site, what does this result in?
Some degree of subarachnoid block.
Describe the complications associated w/ neuraxial anesthesia
Systemic toxicity (less w/ spinals), accidental IV dosing (rare w/ spinals-very placement w/ asp of CSF)
What are the S/S of a high spinal?
High level of sensory & motor blockade, C3-5 paralysis (respiratory arrest), hypotension & apnea.
How are high spinals treated?
ABCs - epi early
Describe the subdural/epiarachnoid space
Potential space between the dura & arachnoid
What occurs w/ an accidental subdural/epiarachnoid blockade?
Unusual presentation-patchy block, high level block, hypotension, respiratory depression, unilateral/bilateral
How is an accidental subdural/epiarachnoid blockade treated?
When does high epidural blockade occur?
With large volumes
How is a high epidural blockade treated?
Supportive, usually resolves w/in 30 minutes
How is a high epidural blockade prevented?
What are the symptoms of a dural puncture?
HA (positional in nature) can be severe-occiput distribution, CN involvement
What can a dural puncture cause?
Subdural hematoma or ICH
How is a dural puncture treated?
Conservative-IV fluids, rest, caffeine, epidural blood patch
What is the success rate of the epidural blood patch?
90-95% provides immediate relief
When should the blood patch be performed?
Sooner the better, no coagulopathy
How does the blood patch work?
Mass effect in epidural space-> ↑ in ICP, blood clots cause a temporary seal
How is the blood patch performed?
Strict sterile technique, same as epidural, draw 20cc of blood from the pt, inject w/o causing pain (nl pressure)
What are the common complaints of pts while receiving blood patches?
Low grade fever, back spasm, radiculopathy, sore back.
What are the common discharge orders after a blood patch?
No lifting for 2 wks, no heavy exercise, tylenol/motrin for pain, heating pad & massage to lumbar musculature, notify MD if radiculopathy, high fever or return of pain
What are the causes of neurologic damage?
Trauma, anterior spinal artery thrombosis, adhesive arachnoiditis, spinal cord compression, injection of a neurolytic agent (accidental, drug toxicity)
What should raise a red flag w/ trauma in regard to neurologic damage?
Describe anterior spinal artery thrombosis.
Rare but catastrophic, rapid, painless permanent paraplegia
How is adhesive arachnoiditis caused and what are the S/S?
Injection of wrong drug (preservatives, betadine, other into CSF)
What causes spinal cord compression, how is it diagnosed & treated?
Immediate decompression laminectomy
Organotomes spinal level for stomach and site of referred pain.
Epigastric or LEFT hypochondrium
Organotomes spinal level for duodenum and site of referred pain.
Epigastric or RIGHT hypochondrium
Organotomes spinal level for jejunum and site of referred pain.
Organotomes spinal level for ileum and site of referred pain.
Organotomes spinal level for cecum and site of referred pain.
Periumbilical or RLQ
Organotomes spinal level for appendix and site of referred pain.
Periumbilical, then to right iliac fossa
Organotomes spinal level for ascending colon and site of referred pain.
Periumbilical or right lumbar
Organotomes spinal level for sigmoid colon and site of referred pain.
Organotomes spinal level for spleen and site of referred pain.
Organotomes spinal level for liver & gallbladder and site of referred pain.
Epigastric-later to right hypochondrium
Organotomes spinal level for pancreas and site of referred pain.
Organotomes spinal level for kidney and site of referred pain.
Small of back, flank
Organotomes spinal level for ureter and site of referred pain.
Loin to groin