Neuraxial Anesthesia: Spinal and Epidural Flashcards
1
Q
How many vertebrae in the spine? Categories of vertebrae?
A
- The building blocks of the spine are the individual bones called vertebrae.
- Cervical (7)
- Thoracic (12)
- Lumbar (5)
- Sacral (5) fused
- Coccygeal (4)fused
2
Q
Features to the vertebrae?
A
-
all vertebrae have a vertebral body (Except C1)
- vertebral body increases in size as you go down the spinal column
-
have 2 pedicles from the vertebral body which join together with lamina
- transverse process for muscle attachmenet
- spinous process also for muscle attachment
-
pedicle with lamina and vertebral body make the vertebral foramen, which houses the spinal cord
- superior and inferior articulating processes/facets
- where adjoining vertebrae articulate
- when 2 vertebral come together, intervertebral foramen is created
- this is where spinal nerves exit the vertebral column
- superior and inferior articulating processes/facets
-
spinous process shape changes down vertebral column
- cervical region- spinous process short and bifid until C7 (vetebral prominent)
- thoracic- spinous process elongated and inferior/posterior direction
- spinous process overlay inferior body of next vertebrae
- lumbar- spinous process is short and hatchet shaped
3
Q
What are the vertebral curves in the supine position?
A
- High
- C5
- L3
- Low
- T5
- S2
4
Q
What are the ligaments of the spinal column? Purpose?
A
- Purpose of ligaments (5 ligaments)
- to Stabilize Vertebral body
- Supraspinous- runs C5-sacrum
-
Interspinous- entire length
- in between each spinous process
- Ligamentum flavum
- Posterior longitudinal ligament- posterior surface of vertebral bodies (C2-sacrum)
- Anterior longitudinal ligament- anterior surface of vertebral bodies (C1-sacrum)
5
Q
What is the ligamentum flavum?
A
- extends from the foramen magnum to the sacral hiatus
- Tough wedge shaped ligament composed of elastin
- Thickest in the mid-line (3-5mm at L3 in adult)
- so-called yellow ligament
- Major landmark for neuraxial anesthesia placement
- will feel needle become anchored. if you let go of the needle, it’ll stick straight out from the skin
-
in young, healthy individuals, this ligament is very robust
- when piercing through ligament, you should feel/here a pop
6
Q
What are the spinal meninges?
A
- Protective membranes continuous with cranial meninges:
- Dura mater
- Arachnoid mater
- Pia mater
7
Q
What is the dura mater?
A
- thickest meningeal tissue
- Begins at foramen magnum and ends caudally at S2/Dural sac (posterior superior iliac spine); S3 in infants
- Abuts the arachnoid mater (subdural space)
8
Q
What is arachnoid mater?
A
second meningeal layer
- Principal physiologic barrier for drugs moving between the epidural space and the spinal cord
- Pressure of CSF pushes arachnoid against Dura Mater
- underneath arachnoid mater is subarachnoid space
- Gives rise to the Subarachnoid space
- house CSF
- Ends at S2; delicate and nonvascular
9
Q
What is the subarachnoid space?
A
- Contains CSF
- Continuous with the cranial CSF and provides vehicle for drugs in the spinal CSF to reach the brain.
- Houses the spinal nerve roots and rootlets
10
Q
What is the pia mater?
A
Adheres to the spinal cord
11
Q
Anatomy of spinal cord?
A
- Foramen magnum to conus medullaris (termination of the spinal cord)- L1-L2
- Spinal cord ends at L1 in adults, L3 in pediatrics
- Gives rise to 31 pairs of spinal nerves
- Each with an anterior root (motor) and posterior root (sensory)
- Roots are in turn composed of rootlets.
-
Conus medullaris ends L1 in adult
- has cauda equina in area
- Cauda equina (ventral/dorsal roots of lumbar and sacral region)
- has filum terminal internum
- comprised of pia mater
- as pierces dural sac–> picks up arachnoid and dura mater form filum terminal externum (anchors SC to coccyx)
- comprised of pia mater
- has cauda equina in area
- Dural sac- ends at S2 (PSIS)
12
Q
Where does the dural sac end?
What composes the cauda equina?
What is the filum terminal internum? filum terminal externum?
A
S2
- Superficial landmark is posterior superior iliac spine (PSIS)
- cauda equina is ventral and dorsal roots of lumbar and sacral region of spinal cord
- filum terminal internum (pia mater) piereces dura sac and picks up arachnoid and dura mater which becomes flium terminal externum
- anchors SC to coccyx
13
Q
What are the components of the nerve roots?
A
- Dorsal/Posterior (sensory) roots—> dermatomes
- Ventral /Anterior (motor/autonomic) roots–> myotome
14
Q
Highlights mentioned for this picture during lecture?
A
- cross section of spinal cord has gray matter (internal H)
- posterior horn- sensory
- anterior horn- somatic/skeletal muscle
- lateral horn
- contains intermediolateral cell column- visceral motor
- T1–> L2/L3
- location of sympathetic visceral fibers
- contains intermediolateral cell column- visceral motor
- white matter (outer aspect)
- dorsal column
- ventral column
- lateral column
- rootlets- form dorsal root (dorsal root ganglion- neuron cell bodies of sensory fibers)
- ventral root and dorsal root form together to make spinal nerve which exits intervertebral foramen
- divides into
- posterior primary rami - innervates deep muscles of back and sensory of back
- ventral primary rami- innervates everything else in body
- divides into
15
Q
What is a dermatome?
Segment?
Which dermatomes do we need to memorize?
A
- The portion of the spinal cord that gives rise to all the rootlets of a single spinal nerve is called a segment
- Dermatome is the skin area innervated by a spinal nerve and its segment
- Cutaneous distribution of spinal nerves
- C6 (thumb)
- C7 (2nd and 3rd finger)
- C8 (4th and 5th finger)
- T4 (nipple)
- T6 (xiphoid)
- T8 (last rib)
- T10 (umbilicus).
16
Q
Volume and SG of CSF?
A
- Volume
- 150 cc subarachnoid space
- CSF volume replaced 3-4 X day
- Produced 21ml/hr by choroid plexus
- Specific gravity
- 1.004-1.008
17
Q
What provides blood supply of spinal cord?
A
- Spinal cord supplied by one anterior spinal artery and two posterior spinal arteries
- anterior spinal artery not sufficient to supply blood to lower/inferior portion of spinal cord and needs radicular branches
- Radicular branches come off of aorta supply these three arteries
- artery of adamkiewicz is important to maintain anterior blood supply to SC
- Two posterior arteries have better continuity of blood supply than the anterior spinal artery
18
Q
What are some targets of neural blockade?
A
- Local anesthetic bathes the nerve roots in that space
-
Sub-arachnoid Block (Spinal Anesthesia)
- Local anesthetic is injected into CSF to directly bathe the nerve root, leads to rapid onset of block
- get very dense blockade in 1-2 minutes
- Local anesthetic is injected into CSF to directly bathe the nerve root, leads to rapid onset of block
-
Epidural Anesthesia
- Local anesthetic is injected into epidural or caudal space and diffuses through the dural cuff before bathing the nerve root, leads to slower onset of block
- with diffusion and baxton plexus (absorbs LA) results in slow and not as profound onset of blockade
- Local anesthetic is injected into epidural or caudal space and diffuses through the dural cuff before bathing the nerve root, leads to slower onset of block
19
Q
Goal of neuraxial anesthesia?
A
- Goal: Blockade of nociceptive impulses
- Nociceptive impulse is a stimulus that causes pain or injury
- Blocks all impulses regardless of fiber type (also order of blockade. Return of sensation happens in REVERSE order)
- Autonomic
- Sensory
- Proprioception
- Motor
-
Autonomic and motor function are also blocked !!
- blocking both dorsal and ventral root
-
Order of fibers blocked (this was not covered adv prin, but covered in previous classes? don’t know if we need this level of detail…)
- B fibers – lightly myelinated, pre-ganglionic ANS fibers
- C fibers – sympathetic, non-myelinated post ganglionic ANS fibers
- C fibers – dorsal root, non-myelinated slow pain fibers – slow pain/ temperature / touch
- A delta – medium myelination, fast pain, temperature touch
- A gamma – medium myelinated, skeletal muscle tone
- A beta – heavy myelinated touch/pressure
- A alpha – heavy myelinated, skeletal muscle, motor, proprioception.
20
Q
What is a differential blockade?
A
Different nerve types have different sensitivities to local anesthetic (LA)
- Autonomic nerves highly sensitive with rapid onset of blockade
- will see decrease in BP and hypotension before loss of sensory/motor
- if blockade high enough, can see bradycardia
- Sensory nerve intermediate sensitivity
- next modality blocked
- Motor nerves more resistant to LA and have slower onset of blockade
- last modality to be blocked
- patient may not be able to sense leg, but will be able to move it until motor is blocked
21
Q
How does the autonomic and motor blockade differ between SAB and Epidural blockade?
A
- Spinal (SAB) Blockade:
- Autonomic blockade 2-6 levels above sensory blockade
- Motor blockade 2 below sensory blockade
- Epidural Blockade:
-
Autonomic blockade same level as sensory blockade
- because of diffusion required through dura/arachnoid mater
-
Motor blockade 2-4 levels below sensory blockade
- iif patient says no feeling at nipple line (T4), autonomic blocked at same T4, cardiac accelerators still intact. not as much bradycardia
-
motor blockade at T6-T8
- not as much of a respiratory blockade c/t spinal
-
Autonomic blockade same level as sensory blockade
Example
-
if patient has SAB and says they can’t feel anything at nipple line, sensory blockade is T4
-
autonomic blockade will be 2-6 levels above that. T1-T4 is where cardiac accelerators are
- so patient will lose ability to regulate heart rate in response to vasodilation that occurs with spinal, causing bradycardia/hypotension
-
autonomic blockade will be 2-6 levels above that. T1-T4 is where cardiac accelerators are
-
if same patient has sensory at T4, motor blockade is T6–> impairs accessory respiratory muscles
- may not matter in young, healthy individual but may matter in pt with resp decline (copd etc)
22
Q
Advantages/disadvantages to neuraxial anesthesia
A
Advantages
- Decreased incidence of DVT, cardiac morbidity and death
- Decreased lower extremity vascular graft occlusion, due to vasodilationà increased tissue blood flow below level of blockade
- Decreased incidence of pneumonia
- minimal pain, get up, move, cough, prevent PNA
- Decreased stress response
- decreased catechol release
- beneficial for pt with CAD
- Avoids airway manipulation
- caution neuraxial technique in those with known difficult airway
-
safest option for known difficult airway is to have control over airway throughout the procedure
- if blockade goes high and limits respiratory drive, then have to deal with difficult airway in middle of sx.
- Decreased incidence of PONV
- Intra and postoperative pain relief
Disadvantages
- Hypotension
- If pt can’t tolerate big drop in BP, may want GA
-
ex- pt withs severe aortic stenosis, CAD
- epidural may be better option because hypotension is not as profoudn
- may decide GA is safer
- Delayed case start
- Failure rate depends on experience
- Not a benign anesthetic
23
Q
Considerations for choosing neuraxial technique?
A
- Anatomy
- Age
- young female in 20s will be easier to place epidural/spinal c/t elder back with arthritic changes/osteoporosis
- Pregnancy
- Pathophysiology/Comorbidities
- mild/mod aortic stenosis should do epidural instead of spinal (more controlled onset of autonomic blockade with epidural)
- severe aortic stenosis- may not want neuraxial technique at all
- Sensory level required vs adverse physiological effects
- if need sensory up to T4, then you’re going to get autnomic blockade that blocks cardiac accelerators. can your pt tolerate that?
- may want to do epidural instead of spinal, because autnomic blockade will also only be at T4 with epidural, leaving cardiac accelerators intact.
- Length of procedure
-
a good spinal anesthetic lasts about 2 hours (can prolong)
- if sx is longer, may need epidural with catheter so you can redose
-
a good spinal anesthetic lasts about 2 hours (can prolong)
- Post-op analgesic needs
- need one shot and done, or will you need the added analgesia postop?
24
Q
Indications for neuraxial anesthesia?
A
- Anesthesia
- Sole anesthetic
- Combined Spinal-Epidural Blockade (CSE)
- want rapid setup of a spinal and prolonged pain control of epidural
- allows you to to spinal and then thread catheter for epidural
- Combined GA/Regional
- Major abdominal procedures
- Lower extremity vascular cases
- Analgesia
- Postoperative
- Labor and Delivery
25
Q
Contraindications to neuraxial anesthesia
A
- Patient Refusal<< only absolute C/I
- Infection at injection site
- may need to go to diff level
- Increased ICP
- Clotting defects/anticoagulant therapy
- know pt PLT level
- need >100 k PLT
- know site protocol
- Severe hemorrhage or hypovolemia
- CNS disease/meningitis
- MS or meningitis for example
- Hysteria/inability to remain still for block placement
- Bacteremia
- Septicemia
- Valvular lesions with fixed stroke volume
- severe AS/MS - maybe just use epidural
- hypertrophic cardiomyopathy
- Difficult airway
- Full stomach- relative
- Peripheral neuropathies- relative. need thorough documentation of baseline abnormalities
26
Q
CV effects of neuraxial block
A
- Loss of sympathetic activity results in vasodilation below level of blockade, decreasing SVR (15-20%)à decreased preload therefore CO (decrease 10-15%).
- Venous dilation > arterial dilation
- If blockade is at or cephalad to T1-T4 the cardiac accelerators are blocked resulting in bradycardia.
- Results in profound hypotension
- Treatment includes: vasopressors, volume load (15ml/kg), +/- vagolytic drug to treat bradycardia
33
Q
What are common landmarks for an epidural?
A
- C7 – vertebra prominens
- T3- scapular spine
- T7 - inferior angle of scapula
- T12- last rib
-
L4- Intercristal line or Tuffiers line = iliac crest
- Lumbar epidural/SA block
- Stay below level of conus medullaris (L1) → SC ends at L1
- S2- posterior superior iliac spine- for caudal epidural
40
Q
Difference in target zone for epidural versus SAB?
A
- Epidural space in red- target zone for epidural
- intrathecal/Subarachnoid space in purple
- if you inject LA, will get sensory (posterior) and motor (ventral) root. will be blocking autonomics as well
-
if LA injected into epidural space, has to absorbed into dura and arachnoid mater in order to get to root/rootlets
- makes epidural blockade slower to setup
42
Q
Which type of spinal needle has increased risk of PDPH?
What is important about the bevel position with this needle?
A
Cutting Needle (Quincke/Pitkin) (usually not used anymore) – in NM maybe.
- Cutting needles actually cut, so it cuts through the fibers
- Increased risk of PDPH due to increased trauma to the dura
- CSF lost: Cutting > Pencil point
- Increased risk of PDPH due to increased trauma to the dura
- Dural “pop” is less likely to be appreciated due to the sharper tip -> “less tactile”
- Introducer may not be necessary depending on patient size
-
Bevel position important!
- Bevel must be parallel to dural fibers → decreases incidence of PDPH (less fibers cut)
Bevel Position:
-
Sitting: bevel facing left/right
- Ex: Dural fibers run longitudinally (head to coccyx)
-
Lateral: bevel up/down
- Ex: longitudinal fibers are running horizontally
- Less force
- More likely to injure cauda equina
48
Q
Considerations of baricity of LA, patient position and spread of LA?
A
Hyperbaric uses:
- Spinal @ lumbar region w/ HYPERBARIC (sitting) = hyperbaric LA heavier/denser than CSF
→ will settle into sacral region (saddle block)
- If immediately laid flat w/ hyperbaric soln → LA will follow gravity and will increase ht/spread block into thoracic area (following T5 low curvsture) and S2 (low curvature)
Hypobaric soln:
- If immediately lay flat → LA will stay at high lumbar curvature (L3)
- If you do the same thing with an isobaric solution and leave them sitting, it will stay in the same area. If you do hypo, it will rise as your pt is sitting – go to brain, this is not advised.*
- Generally, as soon as your done with a spinal, you want to lay your pt down so it will be a nice spread. Iso it will stay there,*
- Hyper -> it will move down to low curves so you’ll get some cephalad spread. (T5/S2)*
56
Q
Technique for caudal anesthetic?
A
“go in until you feel a pop =
- Identify the sacral hiatus and PSIS
- Needle introduced in a slightly cranial direction through the hiatus at 60-degree angle
- The needle is advanced until a “pop” or click is felt as the needle pierces the sacrococcygeal membrane
- The needle is then lowered to a 20-degree angle and advanced an additional 2-3 mm to make sure the bevel is in the caudal epidural space.
- (The dura ends at S2, but may extend further.) – NO BLOOD OR CSF, epidural.
- Confirm placement into sacral hiatus
- Inject 5 ml saline rapidly through caudal needle while palpating the skin overlying sacrum
- Bulge midline = above sacrum (incorrect placement)
- No bulge = aspirate to confirm no blood/CSF → then inject LA anesthetic while feeling for inadvertent subcutaneous injection with the other hand.
- Inject 5 ml saline rapidly through caudal needle while palpating the skin overlying sacrum
- There should be very little resistance to injection.
- If you feel SUBQ air – wrong position, try again.
