3 - Neuraxial Anesthesia Flashcards
How many vertebrae are in the spinal column?
33
Number of vertebrae:
Cervical
Thoracic
Lumbar
Sacral
Coccygeal
7 cervical
12 thoracic
5 lumbar
5 sacral (fused)
5 coccygeal (fused)
The epidural space extends from ____ to ______
foramen magnum
sacral hiatus
Which vertebrae have no epidural fat?
Cervical
Dura Mater
Thickest, outermost meningeal layer
Arachnoid Mater
Laminar layer over the inner surface of the dura
Trabecular spider formations connect the laminar layer to the pia mater
Does the dura or arachnoid membrane most impede drug movement through the meninges?
Arachnoid
Is CSF primarily in the subdural or subarachnoid space?
Why?
Subarachnoid
low permeability of arachnoid mater keeps it from migrating out into the subdural space
What percentage of CSF is water?
99%
Adult total volume of CSF
100-160 ml
What is the main production site of CSF?
Parenchymal Capillaries of the brain and spinal cord
Which direction does CSF flow?
Not unidirectional
Transmitted cardiac oscillations produce local mixing
Where is CSF absorbed?
Parenchymal capillaries of the brain and spinal cord
Which grows faster in a fetus: the spinal cord or the vertebral cloumn?
The vertebral column
Where does the spinal cord end in adults?
Newborns?
L1
L3
How are spinal nerves and dermatomes named in cervical regions?
All other regions?
Lower vertebrae of the foramen they pass through
Upper vertebrae of the foramen they pass through
What is the cauda equina?
the lumbar and sacral spinal nerves that extend beyond the tip of the spinal cord
When using hyperbaric drugs, you should position the operative side ________
down
When using isobaric or hypobaric drugs, you should position the operative side _______
UP
For C/S spinal lying down, which side should the patient lie on?
Right side
Which is usually larger: epidural or spinal needle?
Epidural
What length of catheter should be inserted into the epidural space?
5 cm
The two most important factors that determine the spread and duration of subarachnoid anesthesia are
Density and Dose
How is hyper/hypo/isobaric determined?
It’s the ratio of two densities:
Dnesity of the CSF
Density of the drug
Hyperbaric solutions are ______ dense than CSF
More
How are local anesthetics made hyperbaric?
Mixed with dextrose
In a supine patient, hyperbaric anesthetics will flow to
The upper thoracic region
Vasopressors prolong the effect of _______ in intrathecal anesthesia, but not ________
tetracaine
lidocaine, bupivicaine
How does intrathecal precedex effect duration?
Prolongs the duration of subarachnoid anesthesia and analgesia
What amount of fentanyl is optimal as an adjuvant to spinal analgesia?
Smaller doses are just as effective and cause less itching
How is epidural spread effected by age?
Spreads further in older people
May worsen hypotension
In epidurals, the large the dose, the _________ spread
larger
What is the effect of using sodium bicarb as an adjuvant
Raises the pH, which increases non-ionized circulating amount
Decreases the speed on onset
Inreases the density of block
What is the effect of using A2 agonists as adjuvants?
Epinephrine decreases systemic absorption of the drug
Precedex/Epi/Clonidine improve speed of onset and duration
Who do A2 agonists improve the analgesia of a block?
Stimulation of A2 receptors produces analgesia
Most common complication in obstetric epidural management
Accidental injection of drugs into intrathecal space
What abnormal things are you looking for when test dosing an epidural with lidocaine?
Tingling in feet at 2-3 minutes
Motor loss at 3 minutes
Unrecognized subdural injection would cause what?
Excessive epidural block
Subarachnoid anesthesia occurs mostly in the ________
Spinal nerve roots
How does neuraxial block effect MAC?
Decreases MAC of inhaled volatile gases
What effect does neuraxial anesthesia have on sedatives?
Potentiates their action
Also causes sedation on its own
Why do patients with neuraxial anesthesia lose sensation to a greater degree than motor use?
Sensory fibers are thinner than the large, thick motor fibers
A patient with a sensory block at T10 may have a sympathetic block _______
Much higher
smaller fibers
Sensitivity of fibers to neuraxial anesthesia:
Motor
Sensory
Sympathetic
small
intermediate
large
What happens to CO and SVR after intrathecal block?
Increases
Decreases
What vertebral level is sympathetic stimulation of the heart?
What would happen if it was blocked?
T1-T4
Disproportionate vagal response —-> severe bradycardia
What are the differing effects of using phenylephrine vs ephedrine for neuraxial hypotension?
Phenylephrine will not increase the heart rate, and in fact will decrease it
Ephedrine will increase the heart rate
What are four ways to alleviate N/V with spinal anesthesia?
Fix hypotension
Administer oxygen
Fluids
Zofran
Why does patients with neuraxial anesthesia get nauseated?
Increased vagal activity increases peristalsis
Hypotension causes hypoperfusion of the vomiting trigger chemoreceptor in the medulla
Opiates, when included in the injection
A patient with a Thoracic block and normal respiratory function may still be prone to aspiration. Why?
The abdominal muscles are crucial in coughing
Postdural puncture headaches usually effect the _____ and _____ regions of the head
front
occipital
Which needles are pencil point?
Whitaker
Spratte
What needle is a cutting needle?
Quincke
How often is a blood patch effective in fixing PDPH?
95%
When does PDPH usually develop
24-72 hours after dural puncture
Why does hearing loss sometimes occur with spinal anesthesia?
Decreased CSF pressure reduces the function of the inner ear
When does hearing reduction from spinal anesthesia usually resolve?
Within 1 month
Cervical and thoracic vertebrae have spinous processes that _______________
angle acutely in a caudal direction
Very tight construction and angles, making needle insertion difficult
Why is the lumbar area easier to cannulate?
spinous processes shorter and broader with posterior orientation
Relatively large gaps between processes
What is the average distance from skin to lumbar epidural space?
5cm
Where is the epidural space largest?
midline midlumbar region
Why are midline epidural approaches preferred?
Epidural space is larger anterior to posterior than it is laterally
The plexus is most prominent in the lateral portion
what happens to epidural veins in pregnant women?
Engorged d/t increased abdominal pressure
What is a differential block?
Iterrupts autonomic transmission but not sensory or motor
A sympathetic block can be as much as ______ above the sensory blockade
six dermatomes
Do patients with neuraxial anesthesia have a higher or lower incidence of urine retention that general anesthesia?
Lower
What is selective anesthesia?
small doses of local injected into only the nerve roots inolved in the surgical field
Usually CSE
What type of local anesthetic is used in prone cases?
Hypobaric
Conducting a spinal in a patient with increased ICP may cause
Brain herniation
Which musculoskeletal deformity is a risk factor for CNB complications?
Osteoporosis
What is a double crush phenomenon?
CNB peripheral neuropathy on top of Pre-existing neuropathy
Why is garlic a concerning herbal medication?
How long should it be d/c’d prior to sx?
Inhibits platelet aggregation
Increases fibrinolysis
7 days
Why is ginkgo a concerning herbal medication?
How long should it be d/c’d prior to sx?
inhibits platelet activation
36 hours
Why is ginseng a concerning herbal medication?
How long should it be d/c’d prior to sx?
lowers blood glucose
increases PT/PTT
34 hours
What is the most common pathogen associated with epidural abscesses?
S. aureus
What is the best test for suspected epidural hemorrhage or abscess?
MRI
Which type of heart failure is a relative contraindication to CNB?
preload dependent (hypertrophic, severe Ao Stenosis)
These patients can’t tolerate even short periods of bradycardia or decreased preload from vasodilation
What is specific gravity
density of a substance compared to water
What factors can increases the specific gravity of CSF?
Hyperglycemia
Uremia
Age
What factors can decrease the specific gravity of CSF?
temperature (increased temp)
Bilirubin in the CSF (from jaundice/liver fx)
What is the ratio of specific gravity of an isobaric anesthetic to CSF
1
What is the baricity of a hypobaric solution?
Hyperbaric?
< 0.999
> 1.0015
Name three highly protein bound drugs.
Do they have a long or short duration?
Tetracaine
Bupivicaine
Ropivicaine
Long
Name two low protein-bound drugs.
Do they have a long or short duration?
lidcocaine
mepivicaine
Short
To minimize the risk of PDPH, the epidural needle should be turned _________
with the bevel parallel to dural fibers
How far should a CSE catheter be threaded?
2-3 cm
To avoid PDPH with CSE, how long should the catheter be left in place if possible?
40 hours
Cauda Equina Syndrome
persistent paralysis of the cauda equina nn
lower extremity weakness
bowel and bladder dysfunction
Transient Neurologic Syndrome
pain originating in the gluteal region radiating to both lower extremities
spontaneously resolved within 10 days
Use of spinal lidocaine in CSEs is associated with which two syndromes?
cauda equina
transient neurologic
The sympathetic nerve fibers that innervate the heart are called the _______
cardiac accelerators
What is a 5-HT3 drug?
Why are they used to prevent SIH?
ondansetron
given prophylactically
thought to block the reflexive bradycardia and hypotension caused by sympathetic blockade
In managin SIH when should ephedrine be used?
Phenylephrine?
bradycardia
normal or tachycardia
Ephedrine effects _______ receptors
phenylephrine effects _______ receptors
A and B
A
Bezold-Jarisch Reflex
stimulation of mechanoreceptors in the left ventricle causes bradycardia
What is the largest interlaminar space?
L5
What effect does neuraxial anesthesia have on the bowel?
Unopposed parasympathetic innervation:
Constriction
Increased peristalsis
Sympathetic innervation of the gut originates at
T5-L2
The cauda equina extends from ____ to ______
L1 to S5
To what degre will epinephrien extend the action of lidocaine?
Tetracaine?
Bupivicaine?
A little
A lot
hardly at all
In the supine position, the most dependent level of the spine is at
T4
What is normal CSF pressure?
10-20
Where are the two enlargements of the spinal cord?
Why?
cervical enlargement: C4 to T1 - Brachial Plexus
Lumbosacral: L2 to S3 - Lumbar and sacral plexus
When is a caudal epidural block frequently used?
Neonatal abdominal surgery
What is the preload crystalloid dose?
15ml/kg
The classic epidural test dose is
3ml, 15mg lidocaine
How can CSF be distinguished from saline?
Warm
+ for glucose
Which drugs are associated with increased incidence of POUR?
Opiods, anitcholinergics, sympathomimetics
When performing CSE, _______ should be used for loss of resistance while placing the epidural
Air
Prevents confusion of saline with CSF
A patient who received duramorph intraop develops pruritis, nausea, and ventilatory depression. What may be helpful?
Antiemetics
Narcan for ventilatory depression and pruritis
