Neuraxial Principles Flashcards
ASRA
normal PT (prothrombin time)
What pathway does it measure?
12-14 seconds
* extrinsic pathway
ASRA
Normal International normalized ratio (INR)
What pathway does it measure?
0.8-0.11
- extrinsic pathway
ASRA
Normal Activated Partial Thromboplastin Time (aPTT)
What pathway does it measure?
25-32 seconds
- extrinsic pathway
ASRA
Normal Bleeding Time
what is it related to?
3-7 minutes
- r/t platelet aggregation/activation/adhesion
ASRA
Normal Platelet Levels
150,000 - 300,000 mm3
Intrinsic Pathway Factors
“if you can’t buy the intrinsic pathway for $12, you can buy it for $11.98
- XII, XI, IX, VIII
Extrinsic Pathway Factors
“For 37 cents, you can purchase the extrinsic pathway”
- III, VII
Final Common Pathway Factors
“The final common pathway can be purchased at the five (V) and dime (X) for 1 (I) or 2 (II) dollars on the 13th (XIII) of the month”
- V, X, I, II, XIII
Spine Landmarks
C7
Vertebra Prominens
Spine Landmarks
T3
Root of Spine of Scapula
Spine Landmarks
T7
Inferior Angle of Scapula
- good place to do a thoracic epidural
Spine Landmarks
What is the rib margin from midline @ L1?
10cm
Spine Landmark
L4
Superior Aspect of Iliac Crest
- important for central neuraxial
Spine Landmark
S2
Posterior Superior Iliac Spine
Spine Landmarks
What is the Intercristal line (Tuffier’s Line)?
- A horizontal line that runs across the top edges of the hip bones (iliac crests)
- matches the L4 vertebra
- helps identify spaces b/w vertebra for inserting spinal anesthesia needles
Spine Landmarks
What does the space above Tuffier’s Line align with?
L3-L4 vertebrae
Spine Landmarks
What does the space below Tuffier’s line align with?
L4-L5
Where does the spinal cord end?
- Adults - L1
- Peds - L3
Spine Landmarks
What area does the intercristal line correspond to in infants up to 1 yr old?
L5-S1 intervertebral space
Spine Landmarks
What are the landmarks for caudal anesthesia?
Sacral Cornu
- LA goes in the sacral hiatus that is covered by the sacrococcygeal ligament
Where does the spinal cord start & end?
Starts - Medulla Oblongota (rostral region)
Ends - Conus Medullaris (L1)
*b/w L1-L2 in adults
Where does the cauda equina extend from?
conus medullaris — dural sac
* nerve roots from L2-S5 vertebrae & coccygeal nerve
Where does the dural sac end?
S2 in adults, S3 in infants
Where does the filum terminale extend from?
What is its purpose?
- extends from conus medullaris to coccyx (continuation of pia mater)
- function is to anchor spinal cord to coccyx
Internal Filum Terminale Location
Extends from conus medullaris to dural sac (L1-S2)
External Filum Terminale Location
Extends from dural sac into the sacrum (S2-S5)
What signal does the anterior spinal cord take care of?
Motor
What signal does the posterior spinal cord take care of?
Sensory (S after M - so sensory in the back)
- PS - i love neuraxials
Is the afferent nerve sensory or motor?
sensory - toward the brain (ascending limb)
Is efferent sensory or motor?
motor - away from the brain (descending)
Order of Meningeal layers from outer to inner
- Dura Mater: outermost
- Arachnoid Mater: middle layer
- Pia Mater: innermost (covers the spinal cord)
Where is the epidural space located? What does it contain?
- located outside the dura mater (before the dura)
- contains fat and small epidural veins
Where is the subdural space located?
- potential space b/w dura mater & arachnoid mater
Where is the subarachnoid space located? What does it contain?
- b/w the arachnoid mater and pia mater
- contains CSF - cushions/protects the cord
What is the cranial border of the epidural space?
Foramen Magnum
What is the caudal border of the epidural space?
Sacrococcygeal ligament (S5 - coccyx)
What is the anterior border of the epidural space?
posterior longitudinal ligament
What are the lateral borders of the epidural space?
vertebral pedicles
What are the posterior borders of the epidural space?
ligamentum flavum & vertebral lamina
What are the contents of the epidural space?
- nerves, fatty tissue, lymphatics, blood vessels
What is Batson’s Plexus?
- plexus formed by valveless epidural veins that drain blood from the cord and its linings
When are epidural veins more engorged?
- density increases laterally
- engorged in obesity & pregnancy
When do we do a paramedian approach with epidural placement?
- positioning issues
- spinal deformitities (disc issues)
What is the Plica Mediana Dorsalis?
- band of connective tissue located b/w ligamentum flavum & dura mater
The _______ _______ ________ can act as a barrier in the epidural space & affect how medications spread.
Plica Mediana Dorsalis
What are 4 things we can do to help w/ a unilateral epidural block?
- re-position the pt
- give narcotics (in the epidural)
- pull the catheter out 1cm
- re-do the epidural
Where can epidural anesthesia be done?
- Thoracic
- Lumbar
- Caudal
Where is the SA space located?
b/w the arachnoid & Pia mater
Is the SA space a potential space?
No. It contains CSF, nerve roots, spinal cord
Where is the primary target for a spinal anesthetic?
- SA space
Where is the Subdural space located?
- potential space in b/w the dura and arachnoid mater
What can happen when LA intended for epidural space goes to subdural space?
- can cause a high spinal - med affects larger area than intended
What can happen when LA intended for spinal use is injected into subdural space?
- failed spinal block
What is the tough fibrous shield that protects the spinal cord?
Where is its location?
- Dura mater
- starts @ foramen magnum goes down to dural sac
What is the thin layer of connective tissue that lies beneath the dura mater?
Arachnoid Mater
What is the thin paper meningeal layer attached to the cord?
It is highly ________.
Pia Mater
- vascular
How many spinal vertebrae and nerves are there?
- 33 vertebrae
- 31 nerves
Spinal nerve locations & #
- Cervical - 8
- Thoracic - 12
- Lumbar - 5
- Sacral - 5
- Coccyx -1
What is special about the C1-C7 nerves?
They exit above the corresponding vertebrae
What does the Anterior (ventral) nerve root carry?
- motor (movement) & autonomic body processes info from spinal cord to body
What does the Posterior (Dorsal) nerve root carry?
- sensory information from the body to the spinal cord
What is the clinical significance to understanding sensory dermatomes?
- tells you where your block levels is (sensory)
- important to know for surgical procedures
What are the target nerves for spinal (intrathecal) anesthesia?
- cauda equina (below L1, conus medullaris)
- LA works on myelinated preganglionic fibers of the spinal nerve roots
How does epidural LA work?
- it diffuses through the dural cuff - reaches nerve roots @ level we want to block
Controllable Factors that affecct SPINAL spread:
- Baricity
- pt position
- dose
- site of injection (L3/L4, L4/L5)
Non-controllable Factors that affect SPINAL spread:
- Volume of CSF
* lower volume = higher block
Who are pts that have a lower volume of CSF?
- increased intra-abdominal pressure (obesity, pregnancy, ascites)
- Elderly
What does NOT affect the spread of a SPINAL anesthetic?
- Barbotage
- speed of injection
- orientation of bevel
- addition of vasoconstrictor & other adjuncts (duration)
- Gender
Controllable factors that have a significant affect on EPIDURAL LA spread:
- LA volume (drug related)
- level of injection (procedure related)
- LA dose
Non-controllable factors that significantly affect EPIDURAL LA spread:
- pregnancy
- old age
Controllable Factors that have a small effect on EPIDURAL LA spread:
- LA concentration
- Pt position
Non-controllable factors that have a small effect on EPIDURAL LA spread:
- Height (taller or shorter)
* shorter people need less
Factors that DO NOT effect EPIDURAL LA spread:
- additives in LA
- orientation of bevel
- speed of injection
Where does lumbar LA spread?
cephalad
Where does mid-thoracic LA spread?
balanced b/w cephalad & caudad
Where does cervical LA spread?
caudad
Nerve Fibers
A-alpha
myelination:
function:
diameter:
Block Onset:
- heavy myelination
- function: skeletal muscle (motor), proprioception
- Diameter: 12-20 micrometers
- Block: 4th
Nerve Fibers
A-beta
myelination:
function:
diameter:
Block onset:
- heavy myelination
- function: touch, pressure
- diameter: 5-12 micrometers
- block onset: 4th
Nerve Fibers
A-gamma
myelination:
function:
diameter:
block onset:
- medium myelination
- function: skeltal muslce (tone)
- diameter: 3-6 micrometers
- Block onset: 3rd
Nerve Fibers
A-delta
myelination:
function:
diameter:
block onset:
- medium myelination
- function: fast pain, temp, touch
- diameter: 2-5 micrometers
- block onset: 3rd
Nerve Fibers
B-fibers
myelination:
function:
diameter:
block onset
- light myelination
- function: preganglionic ANS fibers
- diameter: 3 micrometers
- block onset: 1st
Nerve Fibers
C-fibers (sympathetic)
myelination:
function:
diameter:
block onset:
- myelination: none
- function: postganglionic ANS fibers
- diameter: 0.3-1.3 micrometers
- block onset: 2nd
Nerve Fibers
C-fibers (dorsal root)
myelination:
function:
diameter:
block onset:
- myelination: none
- function: slow pain, temperature, touch
- diameter: 0.4-1.2 micrometers
- block onset: 2nd
Nerve Fibers
block onset order (list)
- B-fibers
- C-fibers (sympathetic & dorsal root)
- A-delta, A-gamma
- A-beta, A-alpha
Where is the sensory level of LA block located?
- 2 levels higher than motor blockade
Where is the sympathetic level of LA blockade located?
2-6 levels higher than sensory level (sympathetic chain)
Blockade level example:
T8 location
motor block?
SNS block?
motor: T10
SNS: T2-T6
Why does sensory block happen at a higher level than motor blockade?\
Autonomic?
Sensory requires lower concentrations of LA
- requires even lower concentration levels of LA
Sense block order (first to last)
- temperature (alcohol swab)
- pain (pinprick)
- touch/pressure
What scale is used to assess motor blockade?
What does it evaluate?
Modified Bromage Scale
* evaluates function of lumbosacral nerves – nothing above this!
Modified Bromage Scale
0
no motor block
Modified Bromage Scale
1
- slight motor block
- ex: cannot raise leg but still move knee & foot
Modified Bromage Scale
2
Moderate Motor Block
* ex: cannot raise extended leg or move knee - can move feet
Modified Bromage Scale
3
Complete motor block
* ex: cannot move legs, knees, or feet
What 2 things should we have prepared with every spinal/epidural?
- Ephedrine (HR low)
- Phenylephrine (HR high)
Diaphragm nerve
C4
Heart Nerve
T3-T4
Esophageal Nerve
T4-T5
Stomach Nerve
T8
Liver & Gallbladder Nerve
T8-T11
Small Intestine Nerve
T10
Colon Nerve
T11
Kidney & Testes Nerve
T10-L1
Bladder Nerve
T11-L1
