Spinal Flashcards
Describe the vertebral column
Extends from the foramen magnum to the tip of the coccyx
7 cervical
12 thoracic
5 lumbar
5 sacral
4 coccygeal
Sacral hiatus
Lamina of the last sacral vertebrae is incomplete and bridged only by ligaments
-we use this as a landmark- caudal is not spinal but low lying epidural
Purpose of transverse process
Muscular attachment
When stacked the notches and articulating surfaces of the spine form the:
Intervertebral foramina
Consequence of disc thinning (poor disc health)
Compression impinges spinal nerve exiting intervertebral foramina
Photo of vertebral body anatomy
Pedicle
Connection on either side of the vertebral foramen connecting the lamina and the vertebral body
3 landmark ligaments on the journey to the subarachnoid space
Supraspinous
Interspinous
Ligamentum flavum
Point spinal cord terminates at the conus medullaris
L1
Cauda equina
Nerve pathways that continue in a collection of rootless floating in CSF past the conus medularis
Anchor of spinal cord in sacrum
Filum terminale
Layers of meninges around spinal cord
Dura
Arachnoid
Pia
Pia mater
Covering directly in contact with spinal cord
Space we are aiming for with a spinal block
Subarachnoid, filled with CSF
Epidural space
Continuous POTENTIAL space outside the dural sac but inside the vertebral canal
Distance between the skin and lumbar epidural space
2.5-8cm
Highly variable
What does the epidural space contain?
Veins, fat, lymphatics, segmental arteries, nerve roots
Artery of adamkiewicz
Arises from aorta, typically unilateral providing major blood supply to the anterior, lower two thirds of the spinal cord
Blood supply of the spinal cord
A single anterior spinal artery and paired posterior spinal arteries
Hour many people have left sided artery of adamkiewicz?
75%
Injury to of artery of adamkiewicz
Ischemia
Anterior spinal artery syndrome=
Paralyzed with preserved sensory input
Sensory tract
Dorsal root-posterior
Afferent signaling
Motor signaling
Anterior-ventral root
Efferent
SNS/sympathetic chain
Thoracolumbar innervation
SNS signaling to the body is a blow horn and immediately goes everywhere
Gray ramus
Unmyelinated, post ganglionic
White ramus
Myelinated preganglionic
Impact of local anesthetic on an action potential
Does not let fiber meet threshold so that it can fire
Impact of acidity on locals
Impairment due to ionization
Amount of a nerve that needs to be blocked
3 nodes or
5-6 mm of unmyelinated fibers
Ester metabolism and identification
One i
Hyrolyzed by plasma esterases
Amide metabolism and identification
Two i’s
Lidocaine
Biotransformation in liver
Basic properties of local anesthetics
Weakly basic tertiary amines
Poorly water soluble
Prepared in strong acids
Pka
Ph at which drug is 50% ionized and 50% nonionized
Speed of onset factor with local anesthetics
Pka
Potency of locals and why
Lipid solubility
Axon and myelin sheath are composed of lipids
Factor that impacts duration of action of locals
Protein binding
-the sodium ion channel is the protein!!
Short acting local
Chloroprocaine
30-45 min
Rapid onset short duration, redose every 30 min for surgical anesthesia
Intermediate local (standard)
Lidocaine
1-2% depending on application
Epi increases duration by 50%
NOT USED in spinal-transient neurological symptoms
Mepivacaine
1.5-2%
Intermediate -60-80min
Suitable for ambulatory
Long duration local
Ropivacaine
Less potent and shorter than Bupivacaine
-Lisa hates this for spinals
Bupivacaine
Potent
Duration 150 min (95% protein bound)
What do we not use in hyper allergic patients?
Esters
-break down into PABA
Allergic reactions and locals
Very little cross sensitivity between esters and amides
What do we tell patients who had a reaction at the dentist?
Dentists use large doses of epinephrine in highly vascular locations…. Feels like an adverse reaction but its really just the epi
Variables in LA effect on nerve fibers
Size of fiber
Myelination
Drug concentration achieved and duration of contact
Are C fibers unmyelinated or myelinated?
Unmyelinated
Why do we get sensory block without motor?
Size
Baricity
Ratio of the density of a local anesthetic at a specific temperature compared to the density of CSF at the same temperature
Average block height when injected at height of lumbar lordosis
T4-T6
Supine “high points”= C5, L3
Supine low points of spine
T5
S2
Variables impacting intrathecal LA spread
Volume is less significant than Dose
Site
POSITION- during and immediately following block
Barbotage
Turbulent flow of CSF (pulling back and re-injecting multiple times to check placement)
Three most important modifiable factors in distribution of locals anesthetic (spinal)
Baricity
Position of patient
Dose of anesthetic
Dermatome visual
Cardiovascular considerations with blocks
Sympathectomy- don’t kill your patients with cardiovascular disease;)
Don’t trend patients that get hypotensive with a spinal- you’ll just get better coverage of t1-t4….
Neuraxial blockade and pulmonary
Patients may not be able to feel themselves breathing… but they are!
Usually minimal effect
Mechanism of decreased surgical blood loss with neuraxial blockade
Blocking surgical stress prevents the neuro endocrine stress response that would cause increased bleeding/vascular permeability
Neuraxial and the bladder
Loss of autonomic control results in urinary retention until the block wears off
Absolute contraindications for neuraxial
Patient refusal
Sepsis at site
Coagulopathy or anti coagulation (uncorrected)
Elevated ICP
Uncorrected hypovolemia
Allergy
Two names for spinal anesthesia
Intrathecal injection
Subarachnoid block
Placement of LA below this level of spine in adults and kids helps avoid spinal cord trauma
L1 in adults
L3 in kids
Cutting needle
Quincke
Two pencil point needles
Whitacre and sprottle
3 components of the spinal needle set up
Obturator (stylet)
Spinal needle
Introducer (large bore)
This spinous process is most prominent at the base of the neck
C7
Correlates with the base of the scapula
T7
Usual space/vertebra in line with iliac crests
L4
L4-L5 interspace
How do you know you’re in the subarachnoid space?
CSF
Block level for hip
T10
Block level for vagina/bladder/prostate
T10
Block height for lower extremities
T12
Bromage scale
More common in PACU
Grade I-IV
I-free movement of legs
IV unable to move legs or feet
Alice test
Pinch test for feeling
Two most common complications of neuraxial anesthesia
Failed block
PDPH
Material risk
What the normal human wants to know about
-don’t scare the shit out of your patients
Minor/moderate/major complications of SAB
Best monitor?
Patient
Spinal induced hypotension
Sympathetic blockade-vasodilation
T1-T4 or cardiac reflexes
_load with fluids to compensate for reduced venous return?
PDPH, risk categories
Incidence varies
Reduced risk: older patients, smaller gauge needle, pencil point, BMI>30
Increased risk: female, history of PDPH, large needle
Describe PDPH headache
Postural headache typically either a frontal or occipital headache that radiates
N/V
-thought to be caused by traction or on pain sensitive structures due to leak of CSF/pressure changes
Cranial nerves involved in PDPH
VI and VIII
What is PDPH not associated with?
An aura- this would most likely be a migraine
Treating PDPH
Usually resolves in 5-7 days
-hydration
-caffeine
-NSAIDs
-bed rest
Epidural blood patch after 24 hours
Cauda equina syndrome
Nerve compression leading to motor/sensory Loss of lower extremities
-can be due to neurotoxic effects of LAs, associated with continuous spinals
Epidural hematoma
Less of a risk with SAB
Anticoagulation greatly increases risk
Look at clotting times and platelet count
Symptoms of epidural hematoma formation
Severe back pain
Progression of sensory/motor deficits- block should not progress!!
Index of suspicion should be high if block is lasting longer than expected
Treatment of epidural hematoma
Surgical decompression
-always have an evacuation plan in place if working rurally
Anticoagulation guideline app
ASRA
What we need to have memorized from Anticoagulation table (wait times)
Heparin 4-6 hours prior with normal aPTT
Lovenox (enoxaparin)- >12 hours
Aspirin/NSAIDs-no wait
Common 0.75% Bupivacaine dosing to T10
8-12mg
Chloroprocaine 3% dose t10
30mg
What increases our risk of urinary retention?
Opioid adjuncts
Dosing fentanyl intrathecal
10-20 mcg
What do we do when we dose intrathecal opioids?
Check the label!
You are injecting into the spine-take it seriously
Doses differ between epidural and spinal
Platelet count required for neuraxial
> 100,000
75-100k if stable here
Grams/mL and mg/mL in a 10% solution
10gm/100ml
Or
100mg/ml
