Regional Flashcards
What are the 5 divisions of the spinal column, and how many vertebrae are present in each?
The vertebral column is made up of 33 vertebrae. Cervical- 7, Thoracic -12, Lumbar-5, sacrum- 5 fused, coccyx- 4 fused
What are the anatomic borders of the facet joint?
The facet joint is formed by the superior articular process of one vertebra and the inferior articular process of the vertebra directly above.
Injury to the facet joint can compress the spinal nerve that exits the respective intervertebral foramina, causing pain and muscle spasm along the associated dermatome
What ligament covers the sacral hiatus? what is the significance of this?
The sacral hiatus is covered by the sacrococcygeal ligament.
The ligament is punctured during the caudal approach to the epidural space
order the 5 ligaments of the spinal column from posterior to anterior.
Supraspinous ligament
interspinous ligament
ligamentum flavum
posterior longitudinal ligament
anterior longitudinal ligament
What ligaments are penetrated during the midline approach to the epidural space? how about the paramedian approach?
midline approach: the needle will pass through 3 ligaments
*supraspinous ligament
* interspinous ligament
* ligamentum flavum
Paramedian approach: the needle will pass through 1 ligament
* ligamentum flavum
The paramedian approach bypasses the other ligaments. With either approach the needle should NEVER pass through the anterior or posterior longitudinal ligaments.
List all the structures and spaces between the skin and the spinal cord as they would be encountered during a subarachnoid block.
Skin
subcutaneous tissue
muscle
supraspinous ligament
interspinous ligament
ligament flavum
epidural space
dura mater
subdural space
arachnoid mater
subarachnoid space
pia mater
spinal cord
what happens when you accidently inject local anesthetic into the the subdural space during a SAB? How about during an epidural?
The subdural space is a potential space between the dura mater and the arachnoid mater.
Inadvertent injection of local anesthetic into the subdural space yields the following outcomes:
*Epidural dose-> high spinal with delayed onset (15-20 min)
*spinal dose-> failed spinal
What is Batson’s plexus? and what is its significance?
The epidural veins (Batson’s plexus) drain venous blood from the spinal cord. These valveless veins pass through the anterior and lateral regions of the epidural space.
Obesity and pregnancy increase intra-abdominal pressure, causing engorgement of the plexus. This is associated with an increased risk of needle injury or cannulation during neuraxial techniques.
What is plica mediana dorsalis, and what is its significance?
While its existence remains controversial, many speculate that a band of connective tissue courses between the ligamentum flavum and the dura mater. If it does exist, it could conceivably create a barrier that would impact the spread of medications within the epidural space. The plica mediana dorsalis has long been considered the culprit for difficult epidural catheter insertion as well as unilateral epidural blocks.
What is a dermatome, and which ones are important as you assess neuraxial anesthetic?
the dermatome relates to an area of skin that is innervated by a spinal nerve- it is not necessarily the area of skin that is the same plane as the spinal nerve.
C6- 1st digit (thumb)
C7- 2nd and 3rd digits
C8- 4th and 5th digits
T4- Nipple line
T6- xyphoid process
T10- umbilicus
T12- Pubic symphysis
L4- anterior knee
Compare and contrast the site of action for spinal vs epidural anesthesia.
site of action: Spinal anesthesia
* The primary site of local anesthetic action is on the myelinated preganglionic fibers of the spinal nerve roots.
* Local anesthetics also inhibit neural transmission in the superficial layers of the spinal cord
Site of action : Epidural anesthesia
* Local anesthetics in the epidural space must first diffuse through the dural cuff before they can block the nerve roots
* local anesthetics also leak through the intervertebral foramen to enter the paravertebral area. Here, local anesthetics cause multiple paravertebral blocks
What factors do and do NOT contribute to the spread of local anesthetics in the subarachnoid space?
Significantly affect spread:
Controllable factors:
* Baricity of local anesthetic
* Patient position during and after block placement
* dose
* site of injection
Non-controllable factors:
* VOlume of CSF
* Density of CSF
Does NOT significantly affect spread
* Barbotage
* Increase intra-abdominal pressure (coughing, labor)
* speed of injection
* orientation of bevel
*addition of vasoconstrictor
* weight
*gender
What is the primary determinant of spread for epidural anesthesia?
Volume
Discuss the differential blockade of spinal anesthesia.
Different types of nerves have different sensitivities to the local anesthetic blockade.
* Autonomic fivers are blocked first
* Sensory fibers are blocked second
* Motor neurons are blocked last
Why is this important?
* Autonomic blockade is 2-6 dermatomes higher than sensory block
* sensory block is 2 dermatomes higher than motor block
How is differential blockade different with epidural anesthesia?
There is no autonomic differential blockade with epidural anesthesia
Sensory block is 2-4 dermatomes higher than motor block
Compare and contrast nerve fibers in terms of subtype, myelination, function, size, conduction velocity, and block onset.
Discuss the cardiovascular effects of neuraxial anesthesia.
Sympathectomy vasodilates the arterial and venous circulations, although it predominantly affects the venous capacitance vessels. Consequently, there is a reduction in venous return, cardiac output, and blood pressure. Volume loading with around 15mL/kg and vasopressors will minimize HoTN.
bradycardia is caused by:
* blockade of the preganglionic cardioaccelerator fibers at T1-T4. This promotes a relative increase of parasympathetic tone.
* unloading of cardiac mechanoreceptors (bezold- jarisch reflex)
*unloading of the stretch receptors in the SA node.
Discuss the respiratory effects of neuraxial anesthesia.
In healthy patients, neuraxial anesthesia has negligible effects on minute ventilation, tidal volume, respiratory rate, dead space, and arterial blood gas tensions.
Accessory muscle function is reduced. Impariment of the intercostal muscles (inspiration and expiration) as well as the abdominal muscles (ability to cough and clear secretions) will decrease pulmonary reserve. This is particularly important for the patient with severe COPD.
Apnea is usually the result of brainstem hypoperfusion (decreased blood flow to the ventilatory centers in the medulla).
Apnea is usually NOT the result of phrenic nerve paralysis or high concentrations of local anesthetic in the CSF.
How does neuraxial anesthesia affect the neuroendocrine response to stress?
By inhibiting afferent traffic originating from the surgical site, neuraxial anesthesia diminishes the surgical stress response. This reduces circulating levels of catecholamines, renin, angiotensin, glucose, thyroid-stimulating hormone, and growth hormone
How does neuraxial affect GI function?
The gut receives parasympathetic innervation from the vagus nerve (CN 10) and sympathetic innervation from the sympathetic chain (T5-L2)
Neuraxial local anesthetics inhibit the sympathetic tone, which increases the parasympathetic tone to the gut. This relaxes the sphincters in the gut and increases peristalsis.
How does neuraxial anesthesia affect renal and hepatic blood flow?
So long as systemic blood pressure is maintained, hepatic and renal blood flow and function are unchanged
What is the risk of neuraxial anesthesia in the patient with coagulopathy? What lab values are considered contraindications to a neuraxial technique?
Risk of spinal or epidural hematoma.
Neuraxial blocks are contraindicated in significant pathologic or therapeutic coagulopathic states.
* platelet count <100,00mm
* PT, aPTT, and/or bleeding time twice the normal value
what cardiac pathologies present a risk of hemodynamic collapse with neuraxial anesthesia?
Valve lesions with fixed stroke volume.
* severe aortic stenosis
* severe mitral stenosis
* Hypertrophic cardiomyopathy
what is the risk of a neuraxial technique in the patient with intracranial HTN?
There is an increased chance of brain herniation with sudden change in CSF pressure
What is the relationship between neuraxial anesthesia and multiple sclerosis?
Classic teaching suggests that, while epidural anesthesia is safe, an intrathecal technique may exacerbate symptoms. In practice, there is no good data to support this.
If spinal anesthetic would benefit the patient with MS, you should inform the patient about a small risk of symptom exacerbation.
If you move forward with a spina, understand that demyelinated fibers may be more susceptible to local anesthetic-induced neurotoxicity. It’s best to use a lower dose and concentration of LA.
What is baricity , and how does it influence your selection of local anesthetic?
Baricity describes the density of a local anesthetic solution relative to the CSF.
- An isobaric solution describes a local anesthetic solution whose baricity is similar to CSF.
- A higher density solution is hyperbaric
- A lesser density solution is hypobaric
A hyperbaric solution will sink, a hypobaric will rise, and an isobaric solution will remain in place.
As a general rule, solutions in dextrose are hyperbaric, in saline are isobaric, and in water are hypobaric. Procaine 10% in water is an exception (it’s hyperbaric; presumably because there are so many molecules in a 10% solution).
how does a hyperbaric solution distribute in the sitting patient? how about the supine patient?
A hyperbaric solution will settle to the lowest point of the spinal canal.
- If we keep the patient sitting, a hyperbaric solution will sink and anesthetize the sacral nerve roots, this is a saddle block.
- If we lay the patient supine after the block, a hyperbaric solution will slide down the lumbar lordosis and eventually pool in the sacrum and the thoracic kyphosis.
Hypobaric solution will rise to brain while laying, or lower lumbar region while laying
What are the 2 classifications of spinal needles?
Cutting and non-cutting (pencil point & rounded bevel)
Cutting- quincke, pitkin
Pencil point- sprotte and whitacre
Rounded bevel- green
What are the three different types of epidural needles? How are they different from each other?
Epidural needles differ in the angle of the needle tip. Notice that the needle angle increases in alphabetical order.
- Crawford= 0 degrees
- Hustead= 15 degrees
- Tuohy= 30 degrees
The tuoy needle has the most pronounced curvature. this curvature plus its blunt tip helps prevent dural puncture
How do you dose a caudal anesthetic in a child? An Adult?
Sacral - pediatric -0.5mL/kg / 12-15mL for an adult
Sacral to low thoracic- 1mL/kg/ Adult 20-39mL
Sacral to mid thoracic- 1.25 mL/kg / adult-N/A
What are the absolute and relative contraindications to caudal anesthesia?
Absolute:
* spina bifida
* Meningomyelocele of the sacrum
* Meningitis
Relative
* Pilonidal cyst
* Abnormal superficial landmarks
* Hydrocephalus
* Intracranial tumor
* Progressive degenerative neuropathy
Discuss the mechanism of action of the neuraxial opioids.
Neuraxial opioids inhibit afferent pain transmission in the substantia gelatinosa (lamina 2) of the dorsal horn.
Neurotransmission is reduced by:
* Decreased cAMP
* Decreased Ca2+ conductance (presynaptic neuron)
* Increased K+ conductance (postsynaptic neuron)
Epidural opioids also diffuse into the systemic circulation, where the blood delivers them to opioid receptors throughout the body
DO neuraxial opioids cause sympathectomy, skeletal muscle weakness, and/or changes in proprioception?
Neuraxial opioids do NOT cause:
* sympathectomy
* Skeletal muscle weakness
* Changes in proprioception
Discuss the commonly used intrathecal and epidural opioids dosing
Rank the opioids from most lipophilic to most hydrophilic. How does lipophilicity affect rostral spread in the subarachnoid space?
Hydrophilic drugs tend to remain in the subarachnoid space and travel upwards to the brain (rostral spread)
Lipophilic drugs tend to diffuse out of the subarachnoid space and enter the systemic circulation.
Hydrophilic: Morphine, hydromorphone, meperidine
Lipophilic: Fentanyl, Sufentanil
Compare and contrast PK/PD profiles of hydrophilic and lipophilic opioids used for spinal anesthesia.
What are the 4 most important side effects of neuraxial opioids? What is the most common?
- Pruritis (most common side effect)
- respiratory depression (hydrophilic drugs are higher risk d/t greater rostral spread)
- Urinary retention
- N/V
What local anesthetic can reduce the efficacy of epidural opioids?
2-Chloroprocaine reduces the efficacy or epidural opioids
What neuraxial opioid can reactivate herpes simplex labialis?
Epidural morphine may reactivate herpes simplex labialis type 1. This is best explained by the cephalad spread of the morphine to the trigeminal nucleus. It usually presents 2-5 days after epidural morphine administration.
Describe the pathophysiology and presentation of postdural puncture headache.
Puncturing the dura causes CSF to leak from the subarachnoid space. As CSF pressure is lost, the cerebral vessels dilate. In addition, the brainstem sags into the foramen magnum, which stretches the meninges and pulls on the tentorium. These factors contribute to PDH.
The classic presentation includes a fronto-occipital headache, which may be accompanied by nausea, emesis, photophobia, diplopia, and tinnitus. In the upright position, gravity makes the headache worse, while the supine position brings relief.
Discuss the risk factors for PDPH
Patient factors: Younger age, female, pregnancy
Practitioner factors: Cutting tip needle, larger diameter needle, using air for LOR with epidural, Needle perpendicular to longer-axis of the neuraxis
no effect: early ambulation, continuous spinal catheter (if placed after spinal block)
How do you treat PDPH?
Bed rest
hydration
NSAIDs
Caffeine (cerebral vasoconstriction)
Epidural blood patch
Opioids are not used to treat PDPH
How do you perform an epidural blood patch? what is the success rate?
it is a definitive tx. 90% success rate. if it does not improve after 2, take into consideration other etiologies.
Sterile technique draw 10-20 mL of venous blood and reintroduce to epidural space. When the patient sense pressure in her legs, buttocks, or back the injection is complete.
Useful for two reasons, increase CSF pressure by compressing the epidural and subarachnoid spaces and acts as a plug that prevents further leaks.
What are the common side effects of an epidural blood patch?
The most common side effects are backache and radicular pain.
What is the primary risk of neuraxial anesthesia in the anticoagulated patient? how does the complication present?
The risk of epidural hematoma is similar during block placement and catheter removal.
An epidural hematoma can cause paralysis. Presenting symptoms include lower extremity weakness, numbness, low back pain, and bowel and bladder dysfunction. Surgical decompression within 8 hrs offers the best chance of recovery.
Know this table
Know this table
Know this table
Compare and contrast the level of the conus medullaris and dural sac in the adult vs infant.
The spinal cord ends in a taper as the conus medullaris.
Adult: L1-L2
Infant: L3
The subarachnoid space terminate at the dural sac.
Adult: S2
Infant: S3
Notice the infant has the number 3 in both answers
What is the cause of cauda equina syndrome? What factors increase the risk?
Cause:
Neurotoxicity is the result of exposure to high concentrations of local anesthetic.
Factors that increase risk:
*5% lidocaine and spinal microcatheters.
*Micro catheters focus local anesthetic on a small area of the cord, exposing this region to a high concentration of LA.
How does cauda equina syndrome present? What is the tx?
S/Sx:
* Bowel and bladder dysfunction, sensory deficits, weakness, and/or paralysis
tx: supportive
what is the cause of transient neurologic symptoms? What factors increase the risk?
Cause: Patient positioning, stretching of the sciatic nerve, myofascial strain, and muscle spasm. It is highly unlikely that neurotoxicity causes TNS
Factors that increase risk:
* Lidocaine, lithotomy position, ambulatory surgery, and knee arthroscopy
typically observed after the use of spinal lidocaine
How do transient neurologic symptoms present? What is the treatment?
S&Sx:
*severe back and butt pain that radiates to both legs.
* it generally develops within 6-36 hrs and persists for 1-7 days
Tx:
*NSAIDs, opioid analgesics, and trigger point injections
What is the most common organism responsible for post-spinal bacterial meningitis?
When placing a neuraxial block, there are two routes by which an infectious organism can reach the CSF.
*Failure of aseptic technique
* Bacteria in the patient’s blood at the time of SAB
Streptococcus viridans is one of the most common culprits responsible for post-spinal bacterial meningitis. It is commonly found in the mouth, and this is why it’s so critical to wear a mask while performing and neuraxial block.
what is the best way to prepare the skin prior to neuraxial anesthesia?
Suitable methods to prepare the skin for neuraxial anesthesia include: chlorhexidine, isopropyl alcohol, and iodine solutions.
According to Miller, the best method is a combination of chlorhexidine and isopropyl alcohol.
Chlorhexidine is neurotoxic, so it’s imperative that you allow it to dry completely before you penetrate the skin with the needle
Be able to identify brachial plexus anatomy on ultrasound for an interscalene block.
Know this table
Describe the sensory innervation to the lower extremity.
Describe the sensory innervation of the foot and ankle
Describe the nerves location in cross section
