Neuraxial blocks 3 Flashcards
_____ is the primary determinant of epidural block height
Volume
The initial dosing for epidural is
1-2 mL per segment to be blocked
The “top-up” dose for epidurals is
50-75% of the initial dose
A “top-up” dose should be administered
before the block recedes more than 2 dermatomes
The volume of the epidural space is smaller in the thoracic region when compared to the lumbar region. Therefore, for a given volume of local anesthetic, you’ll achieve ______ spread in the thoracic region as compared to the lumbar region.
Greater
________ is the primary determinant of epidural block density
Concentration
The following drugs can be used for epidural dosing
2-chloroprocaine 3%
lidocaine 2%
ropivacaine 0.1-0.75%
bupivacaine 0.0625-0.5%
levobupivacaine 0.0625-0.5%
Describe the onset of action for chloroprocaine, lidocaine, ropivacaine, bupivacaine, and levobupivacaine for epidural use.
2-chloroprocaine- 5-15 minutes
lidocaine- 10-20 minutes
ropivacaine, bupivacaine, and levobupivacaine 15- 20 minutes
Identify the MOST appropriate techniques for subarachnoid block in a patient scheduled for hemorrhoidectomy.
a. lidocaine 5% in 7.5% dextrose and the sitting position
b. bupivacaine 0.3% in water and the jackknife position
c. Tetracaine 0.2% in water and the sitting position
d. procaine 10% in water and the jackknife position
a & b.
______ describes the density of a local anesthetic solution relative to the CSF
Baricity
When injected inside the subarachnoid space, a hyperbaric solution will
sink
When injected inside the subarachnoid space, a hypobaric solution will
rise
When injected inside the subarachnoid space an isobaric solution
will remain in place
As a general rule, solutions in dextrose are______
hyperbaric
As a general rule, solutions in saline are _____
isobaric
As a general rule solutions in water are______
hypobaric
_________ is an exception to the general rules of baricity because it contains many molecules making it hyperbaric
Procaine 10% in water
If we are using a hyperbaric solution and we keep the patient in the sitting position after the block,
a hyperbaric solution will sink and anesthetize the sacral nerve roots causing a saddle block
If we lay a patient supine after a block with a hyperbaric solution, the solution will
slide down the lumbar lordosis and eventually pool in the sacrum and the thoracic kyphosis (pools low)
If we keep the patient in the sitting position after a hypobaric block, the solution will
rise towards the brain
How does neuraxial anesthesia affect respiratory mechanics?
a. impaired inspiration
b. impaired expiration
c. no impairment
d. impaired inspiration and expiration
D. - accessory muscle function is reduced by neuraxial blockade
Systemic effects of neuraxial anesthesia to the cardiovascular system include
hypotension
vasodilation
variable effect on HR & CO
bradycardia
How can neuraxial anesthesia result in bradycardia?
inhibition of cardioaccelerator fibers at T1-T4
unloading of ventricular mechanoreceptors–> Bezold-Jarisch reflex
unloading of the stretch receptors in the SA node
What are the respiratory effects of neuraxial anesthesia.
in healthy patients has negligible effects on minute ventilation, tidal volume, RR, dead space, and arterial blood gas tension
accessory muscle function is reduced including impairment of the intercostal and abdominal muscles resulting in decreased pulmonary reserve
Describe the CNS effects of neuraxial anesthesia
drowsiness
Describe the neuroendocrine effects of neuraxial anesthesia
diminished sympathetic response to surgical stress
Describe the gastrointestinal effects of spinal anesthesia
relaxation of sphincters and increased peristalsis
Describe the effects to the kidney and liver when performing neuraxial anesthesia.
as long as systemic blood pressure is maintained, hepatic and renal blood flow and function are unchanged
What spinal levels give rise to the cardioaccelerator fibers?
T1-T4
What reflex contributes to asystole that occurs with spinal anesthesia?
Bezold-Jarisch reflex- the heart slows to allow it adequate time to fill
How does a spinal to T4 affect minute ventilation in healthy patients?
it has a negligible effect
What is the most likely cause of apnea due to spinal anesthesia
Brainstem hypoperfusion (not phrenic nerve paralysis or high concentrations of LA in the CSF
When compared to intrathecal fentanyl, which findings are MORE likely with intrathecal morphine?
a. wider band of analgesia
b. increased risk of nausea
c. late respiratory depression
d. higher plasma concentration
e. faster onset
f. sympathectomy
A, B, C
An opioid deposited into the intrathecal space can easily
diffuse into the spinal cord
An opioid deposited into the epidural space must first diffuse across _________ before entering the CSF. Some of the drug also diffuses into the __________.
dural cuff; bloodstream
Neuraxial opioids inhibit
afferent pain transmission in the substantia gelatinosa (lamina 2 of the dorsal horn)
Neuraxial opioids do NOT cause:
sympathectomy, skeletal muscle weakness, changes in proprioception
______ is the most lipophilic opioid, and _____ is the most hydrophilic opioid.
Sufentanil; morphine
Key characteristics of lipophilic opioids include
a shorter duration of action, less spread in the CSF, and risk of early respiratory depression
Key characteristics of hydrophilic opioids include
longer duration of action, greater spread in the CSF, and risk of early and late respiratory depression
When combined with local anesthetics, ______ create a denser block
neuraxial opioids
Identify the MOST common side effect of neuraxial opioid administration.
A. pruritus
B. respiratory depression
C. urinary retention
D. Nausea & vomiting
A. pruritus
The four key side effects of neuraxial opioids include:
pruritus
respiratory depression
urinary retention
Nausea & vomiting
Respiratory depression is more common with_______- in neuraxial opioid administration.
high opioid doses
co-administered sedatives
low lipid solubility (hydrophilic)
advanced age
opioid naivety
increased intrathoracic pressure
__________ is most common in young males, and it’s more common with neuraxial opioids when compared to IV and IM administration.
Urinary retention
_________ reduces the efficacy of epidural opioids.
2-Chloroprocaine
Epidural morphine may _________ in obstetric and postpartum patients.
reactivate herpes simplex labialis
Any opioid that enters the systemic circulation becomes available to
cross the placenta and enter the fetus
When treating pruritus related to intrathecal injection of opioids, what medications should be given?
can be treated with an opioid antagonist such as naloxone
diphenhydramine doesn’t fix the cause, but its sedative effects may be beneficial
Nausea and vomiting is caused by activation of the opioid receptors in the
area postrema of the medulla and vestibular appartus
Transfer of opioids from the epidural space to breast milk is
minimal
What is the mechanism of neuraxial opioid-induced urinary retention?
inhibition of sacral parasympathetic tone. this causes bladder detrusor muscle relaxation and urinary sphincter contraction
