Spinal & Epidural Anesthesia Flashcards
Spinal Cord - general
- cord is approx 25 cm shorter than vertebral canal
- enlarged @ C5-7 (brachial plexus) & L2-3 (lumbar & sacral plexus)
- extends from medulla oblongata to L2 (adult) or L3 (peds)
Cauda Equina
- long roots of lumbar and sacral nerves
- extends from L1-S5
Intervertebral Foramina
- superiorly and inferiorly larger
- lateral notches
- allow for passage of nerves
What forms the facet joint?
superior and inferior articular surfaces and lateral notches
Regional Variation: Cervical & Thoracic
-spinous processes are more angled - need more cephalad angle for needle
Regional Variation: Lumar
-larger vertabra, less overlap and larger gaps
Regional Variation: Sacrum
- fused section of vertebra
- sacral hiatus- lamina of last vertebra is incomplete, bridged by ligaments
Caudal Block Landmarks
PSIS
SC
SH
TC
Abnormal Curvatures
scoliosis - lateral
kyphosis - posterior
lordosis - anterior
3 Ligaments
Supraspinous (superficial)
Intraspinous
Ligamentum Flavum (deep)
Ligamentum Flavum
-thickest, “V shaped”
Epidural Space: location, origination and end
lies between ligamentum flavum and dura mater
-contiguous from base of cranium to sacral sulcus
Epidural Space: distance from skin
- varies with level, loosely correlated with weight
- midline, lumbar approach = 2.5-8cm, average 5 cm
Epidural Space: Contents
- veins (valveless, engorge during pregnancy), fat, lymph, segmental arteries and nerve roots
- potential space is largest lumbar >thoracic>cervical
Spinal Cord: Layers
Dura Mater
Arachnoid Mater (holds CSF)
Pia Mater
Spinal Nerves
31 pairs 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
Thoracic nerves & CT placement
-thoracic nerves run along inferior margin of rib, so place a chest tube at superior aspect of rib
Level and vertebra
-cervical correlate with vertebra below, after T1, correlates with vertebrae above
Dorsal
entering sensory root
Ventral
outgoing motor root
H-shaped central gray region…
neuronal cell bodies and unmyelinated fibers, surrounded by white matter (fiber tracts)
Grey Matter
subdivided into 12 laminae of rexed
I-VI = afferent tracts (receive sensory info)
VII - IX = ventral tracts - motor neurons, interneurons involved in motor functions
Lamina II
substanca gelatinosa
White Matter
- organized
- dorsal white - almost exclusively ascending sensory
- lateral & ventral white - descending motor tracts, most cross over at some point
What can the lateral and ventral white matter do?
- ascend to the brain
- associate trat originate and terminate entirely within spinal cord (reflexes)
Sensory Pathways
afferent (ascend)
-transmit pain & temp (epidermis), pressure, touch, vibratory, proprioception (dermis)
2 Classifications of receptors
1 - extroceptors (near surface of skin and oral mucosa)
2 - proprioceptors (deeper skin layers, joint capsules, ligaments, tendons, muscles and periostium)
2 Main Sensory Tracts
Dorsal Column - Medial Lemniscus
Anterolateral Pathway
Dorsal Column - Medial Lemniscus
- carries signals upwards towards the medulla in dorsal column tract
- crosses over at medulla
- carried through brainstem to thalamus in medial lemniscus tract
Anterolateral Pathway
- originates in dorsal horn to laminae I, IV, V, VI where they synapse
- immediately cross over in anterior commissure to anterior and lateral white columns
- go to brainstem or thalamus
Dorsal Column Medial Lemniscus - characteristics
fibers: large, myelinated
conduction speed: 30-110 m/sec
spatial orientation: high with respect to origin
-discrete types of mechanoreceptive sensations
Anterolateral system
fibers: small, myelinated
conduction speed: few - 40 m/sec
spatial orientation: low with respect to origin
-broad spectrum of sensory modalities - pain, warmth, cold, crude touch
SNS
- preganglionic neurons (b fibers, small)
originate: intermediolateral gray horn btwn T1-L2/3 - exit spinal cord via ventral nerve root - white rami communicans
Cervical Ganglia
-divided into superior, medial and inferior ganglia
Cervical Ganglia: SNS stim of superior…
mydriasis (contract radial muscle of eye)
relaxation of ciliary muscle
constriction of blood vessels of head
Damage to superior cervical ganglia, central SNS damage or injury to other paravertebral ganglia..
miosis (small pupil), ptosis (droopy lid), anhydrosis (no sweat)
aka horner’s syndrome
Inferior cervical ganglia fuses with ___ to form the _____
inferior cervical ganglia fuses with the first thoracic to form the stellate ganglia (C5-6)
Pain and temp pathway
some fibers in dorsal horn give off branches that synapse with internuncial neurons - synapse with ventral horn
-part of reflex response to pain
Dermatomes
T4 - nipple line
T 6-7 - xiphoid process
T 10 - belly button
Motor Pathways
motor/efferent (exit) - info from brain to voluntary muscles, smooth and cardiac muscles and some glands
Corticospinal tract
- supplies voluntary muscles of the trunk and extremities
- originates in large, upper motor neurons located in PREcentral gyrus
Damage to corticospinal tract neurons
-located antrior to precentral gyrus
damage = lower motor neurons can overfire (hyperreflexia) or fire simultaneously (spasticity)
Upper motor neuron paralysis
reflexes intact, suppressor fibers impeded, hyperreflexia occurs
Damage to lower motor neurons
produce flaccid type paralysis
Which two disease processes effect the corticospinal tract?
cerebral palsy and ALS
Pro’s of spinal anesthesia
less adverse in-hospital outcomes, less NV, urinary retention, less opioids, less hospital length of stay
-more mental alertness, long term pain control (epidural)
Uptake & Spread from subarachnoid space
- concentration of LA in CSF
- surface area of nerve tissue exposed
- lipid content of nerve tissue
- blood flow
Distribution
baricity, position, dose
Spinal Anesthesia Physiologic changes
- liver - no change if MAP maintainted
- CV - sympathectomy (block height)
- hypotension and bradycardia
- venodilation >arterial dilation
GI- SNS innervation from T6-12 - increased secretions, sphincters relax, bowel constricts
Spinal - prone position
- can use of pt in this position for surgery
- iso or hypobaric
Process
ID iliac crests (L4-5 clean skin drape ID level to block local (use as finder) approach - median, paramedian, taylor
Parethesia
- stop advancing
- remove stylet and check for CSF
PDPH
- up to 25% incidence
- relief when supine
tx: fluids, caffeine, bed rest, analgesics, sumatriptan - can take 1-6 wks to resolve
epidural blood patch 1-2 times
1st sign of CV collapse following spinal…
bradycardia
Epidural
level L2-4, can use adult levels after age 8
Epidural below T4
vasomotor tone controlled by T5-L1
decreased venous return and subsequent decrease CO
Epidural above T4
T1-4 cardiac sympathetic fibers
profound hypotension and brady
Concentration
lower - sensory
higher - may get motor
Key factor,,
volume
adults: 1-2 mL for each level to be blocked
lumbar gets more spread cephalad than caudal
thoracic even spread up and down
-position is not considered a factor
Does age effect epidural dose?
yes, increased age = decreased dose
Epidural height
<5'2" = used 1 mL per level >5'2" = increase by 0.1 mL for each 2"
Epidural: Pregnancy and Obesity
decrease dose, epidural veins engorged
Epidural: Subdural injection
-delayed high spinal
Epidural: Subarachnoid injection
-immediate high spinal
