Unit 8 - Neuraxial Anesthesia Flashcards
curves of the spine
- Cervical & lumbar lordosis
- Thoracic & sacral kyphosis
what are the 5 divisions of the spinal column and how many vertebrae are in each
cervical = 7
thoracic = 12
lumbar = 5
sacral = 5 (fused)
coccyx = 4 (fused)
anterior and posterior segments of vertebrae
anterior segment = body
posterior segment = vertebral arch
connects anterior and posterior segments of vertebrae
laminae & pedicles
where do anterior and posterior vertebra segments connect
vertebral foramen
contained in vertebral foramen
spinal cord
nerve roots
epidural space
serves as a landmark to determine midline
spinous process
what vertebral level corresponds with the spine of scapula
T3
what vertebral level corresponds with PSIS
S2
what vertebral level corresponds with superior aspect of iliac crest
L4
what vertebral level corresponds with vertebral prominens
C7
what vertebral level corresponds with inferior angle of scapula
T7
what vertebral level corresponds with rib margin 10 cm from midline
L1
angle of spinous processes in cervical and thoracic vertebrae
caudad
requires more cephalad approach with needle
angle of spinous processes in cervical and thoracic vertebrae
caudad
requires more cephalad approach with needle
why is epidural/intrathecal access easier in lumbar vertebrae vs. cervical or thoracic
posterior direction of spinous processes
what provides stability & support to transverse & vertebral processes
muscular attachment
allow head rotation at atlantoaxial joint
C1 (atlas) and C2 (axis)
separates each vertebra and acts as a shock absorber
intervertebral disc
where do spinal nerves exit the vertebral column
via interverbal foramina
what forms anterior border of intervertebral foramina
vertebral body and intervertebral disc
what forms posterior border of intervertebral foramina
facet joints
how can disc degeneration cause nerve compression
can decrease size of intervertebral foramina
s/s spinal nerve compression
pain
parasthesia
motor deficits
how are facet joints formed
inferior articular process of vertebra directly above and superior articular process of vertebra below
guide & restrict movement of vertebral column
facet joints
what is Tuffier’s line
Intercristal line
Horizontal line drawn across the superior aspects of the iliac crest that connects L4 vertebra
what is the interspace above Tuffier’s line
L3-L4
what is the interspace below Tuffier’s line
L4-L5
Tuffier’s line in infants up to 1 year correlates with:
L5-S1 interspace
the sacral hiatus coincides with:
S5
provides entry point to epidural space in sacral area
sacral hiatus
what is the sacral cornua
- Bony nodules that flank sacral hiatus
- Results from incomplete development of facets
what is the conus medullaris
where spinal cords ends in a taper
* Adult = L1-L2
* Infant = L3
cauda equina
bundle of spinal nerves extending from conus medullaris to the dural sac
Comprised of nerves & nerve roots from L2-S5 nerve pairs and coccygeal nerve
where subarachnoid space terminates
dural sac
* Adult = S2
* Infant = S3
Filum Terminale
- Continuation of pia mater caudal to conus medullaris
- Anchors spinal cord to coccyx
where is filum terminale fixated
at conus medullaris & coccyx
internal position of filum terminale
extends from conus medullaris to dural sac
external position of filum terminale
extends from dural sac into sacrum
Structures needle will pass through when performing a spinal anesthetic, midline approach
skin - SQ tissue - supraspinous ligament - interspinous ligament - ligamentum flavum - epidural space - dura mater - subdural space - arachnoid mater - subarachnoid space
runs most of the length of the spine, joins tips of spinous processes
Supraspinous ligament
anatomy of the interspinous ligament
travels adjacent to & joins spinous processes
what is the ligamentum flavum
2 flat flava that run length of spinal canal to form dorsolateral margins of epidural space
where is the ligamentum flavum thickest
lumbar region
what causes loss of resistance when needle enters epidural space
piercing the ligamentum flavum
where does the Posterior longitudinal ligament travel
along posterior surface of vertebral bodies
attaches to anterior surface of vertebral bodies & extends entire length of spine
Anterior longitudinal ligament
what ligaments does the needle pass through in midline approach
1) supraspinous ligament 2) interspinous ligament 3) ligamentum flavum
what ligament does the needle pass through in a paramedian approach
ligamentum flavum only
what is the Taylor approach
- Variation of paramedian performed at L5-S1 interspace
- Needle entry site: 1 cm medial & 1 cm inferior to posterior superior iliac spine
- Needle when inserted 45-55 degrees cephalad & directed medially
3 meningeal layers of spinal cord (outside in)
DAP – dura, arachnoid, pia
in the adult, what correlates with the termination of the dural sac?
superior iliac spines (S2)
what correlates with the sacral hiatus and sacrococcygeal ligament
S5
what correlates with the iliac crests
Tuffier’s line
used as landmarks for caudal anesthesia
sacral cornua
what spinal level coincides with the conus medullaris in an adult
L1-L2
what spinal level coincides with the conus medullaris in an infant
L3
what spinal level coincides with dural sac in an infant
S3
- supraspinous ligament
- interspinous ligament
- ligamentum flavum
- posterior longitudinal ligament
- anterior longitudinal ligament
what forms the dorsolateral margins of the epidural space
2 flava of ligamentum flavum that run the length of the spinal cord
- supraspinous ligament
- interspinous ligament
- ligamentum flavum
- posterior longitudinal ligament
- anterior longitudinal ligament
- spinal cord
- pia mater
- subarachnoid space
- arachnoid mater
- subdural space (potential space)
- dura mater
- epidural veins
- epidural space
- ligamentum flavum
where is epidural space deepest
lumbar region
where does the epidural space end
at the sacrococcygeal ligament
borders of the epidural space
- Cranial: foramen magnum
- Caudal: sacrococcygeal ligament
- Anterior: posterior longitudinal ligament
- Lateral: vertebral pedicles
- Posterior: ligamentum flavum & vertebral lamina
how does the epidural space communicate with paravertebral space
via intervertebral foramina
contained in intervertebral foramina
nerve roots, fat pads, blood vessels
how does the intervertebral foramina affect bioavailability
acts as a lipid sink, decreasing bioavailablility
(bupivacaine > lidocaine/fentanyl > morphine)
how does the intervertebral foramina affect bioavailability
acts as a lipid sink, decreasing bioavailablility
(bupivacaine > lidocaine/fentanyl > morphine)
what is batson’s plexus
epidural veins that drain venous blood from spinal cord
why do obese and pregnant patients have increased risk for needle injury or cannulation during neuraxial techniques
increased IAP leads to plexus engorgement
what is the plica mediana dorsalis
band of connective tissue that courses between ligamentum flavum and dura mater
existence is controversial
what is the plica mediana dorsalis
band of connective tissue that courses between ligamentum flavum and dura mater
existence is controversial
Considered culprit for difficult epidural catheter insertion & unilateral epidural blocks
plica mediana dosalis
1st meningeal layer
dura mater
where does the dura mater begin and end
Begins at foramen magnum, ends at dural sac
what is the subdural space
Potential space between dura mater & arachnoid mater
thin layer of connective tissue that neighbors dura mater
arachnoid mater
2nd meningeal layer
thin layer of connective tissue that neighbors dura mater
arachnoid mater
2nd meningeal layer
what is contained in subarachnoid space
CSF, nerve roots, rootlets, spinal cord
target when performing spinal anesthetic
subarachnoid space
target when performing spinal anesthetic
subarachnoid space
layer deep to arachnoid mater
subarachnoid space
when is a characteristic “pop” felt while administering a spinal block
when needle passes through dura mater
external covering of spinal cord
pia mater
how many spinal nerves are in the spinal cord
31 paired nerves
what forms each spinal nerve
each formed by a posterior (dorsal) nerve root or anterior (ventral) nerve root
which nerve root carries sensory information
posterior (dorsal)
which type of nerve root carries motor and autonomic information
anterior (ventral)
what is a dermatoma
an area of skin that’s innervated by a dorsal (sensory) spinal nerve
cutaneous innervation of C6 nerve root
1st digit (thumb)
cutaneous innervation of C7 nerve root
2nd and 3rd digits
cutaneous innervation of C8 nerve root
4th and 5th digits
cutaneous innervation of T4 nerve root
nipple line
cutaneous innervation of T6 nerve root
xiphoid process
cutaneous innervation of T10 nerve root
umbilicus
cutaneous innervation of T12 nerve root
pubic symphysis
cutaneous innervation of L4 nerve root
anterior knee
sensory input to the face
from 3 branches of trigeminal nerve (CN 5) - NOT a spinal nerve
- V1 = ophthalmic n.
- V2 = maxillary n.
- V3 = mandibular n.
sensory input to the face
from 3 branches of trigeminal nerve (CN 5) - NOT a spinal nerve
- V1 = ophthalmic n.
- V2 = maxillary n.
- V3 = mandibular n.
sensory level neuraxial block required for upper abd. surgery, c-sections, cystectomy
T4 (nipple line)
sensory level neuraxial block required for lower abd surgery, appendectomy
T6-T7 (xiphoid process)
sensory level neuraxial block required for THA, vaginal delivery, TURP
T10 (umbilicus)
sensory level neuraxial block required for lower extremity surgery
L1-L3 (inguinal ligament)
sensory level neuraxial block required for foot surgery
L2-L3
sensory level neuraxial block required for hemorrhoidectomy
S2-S5
epidural catheter insertion location for thoracic surgery, spread pattern, and dosing
thoracotomy, thoracic aneurysm, breast surgery
- catheter: T2-T6 (upper thoracic)
- spread pattern: T2-T6
- dosing: 5-10 mL LA
epidural catheter insertion location, spread pattern, & dosing for abd surgery
gastrectomy, esophagectomy, pancreatectomy, hepatic resection
- catheter: T6-L1 (lower thoracic)
- spread: T1-L4
- dosing: 10-20 mL LA
epidural catheter insertion location, spread pattern, & dosing for lower extremity surgery
TKA, THA
- catheter: L2-L5
- spread: T8-S5
- dosing: 20 mL LA
advantages of thoracic epidural over lumbar epidural
- superior analgesia
- minimizes surgical stress response
- reduces the incidence of postop pulmonary complications
- can spare nerves that innervate legs (allows for postop ambulation)
increased risks assoc. with thoracic epidural + GA
- bradycardia (blockade of cardioaccelerator nerves)
- hypotension
- changes in airway resistance (increased vagal influence on airways)
primary site of action for spinal anesthetic
LA action on myelinated preganglionic fibers of spinal nerve roots
LAs also inhibit neural transmission in superficial layers of spinal cord
primary site of action for spinal anesthetic
LA action on myelinated preganglionic fibers of spinal nerve roots
LAs also inhibit neural transmission in superficial layers of spinal cord
LA site of action for epidural anesthesia
- LA 1st diffuses through dural cuff before anesthetizing nerve roots
- LAs also leak through intervertebral foramen to enter paravertebral area
factors that significantly affect spread of spinal anesthesia
Controllable factors:
- Baricity of LA
- Patient position
- Dose
- Site of injection
Non-controllable factors:
- Volume of CSF
- Density of CSF
most reliable determinant of intrathecal spread when using hypo- or isobaric solution
dose
most reliable determinant of intrathecal spread when using a hyperbaric solution
Baricity
factors that significantly affect spread of epidural anesthesia
Controllable factors:
- LA volume
- Level of injection
- LA dose
Non-controllable factors:
- Pregnancy
- Old age
factors that have a small effect on epidural LA spread
Controllable factors:
- LA concentration
- Patient position
Non-controllable factors:
- Height
- Body weight
- Pressure in nearby body cavities
most important drug-related determinant of epidural spread
LA volume
most important procedure-related determinant of epidural spread
level of injection
typical spread of lumbar epidural
mostly cephalad
typical spread of midthoracic epidural
equally cephalad and caudad
typical spread of cervical epidural
mostly caudad
what is differential blockade
For a given LA dose, the heights of motor, sensory, and autonomic block will be different
level of sensory block is (higher/lower) than motor block
higher
Sensory fibers (pain and touch) are blocked by LA concentrations that don’t affect motor neurons
level of sensory block is (higher/lower) than motor block
higher
Sensory fibers (pain and touch) are blocked by LA concentrations that don’t affect motor neurons
level of SNS block is (higher/lower) than sensory and motor block
higher
SNS fibers blocked by LA concentrations that don’t affect sensory or motor neurons
level of SNS block is (higher/lower) than sensory and motor block
higher
SNS fibers blocked by LA concentrations that don’t affect sensory or motor neurons
sensory block in spinal anesthesia in relation to motor block
sensory block is 2 dermatomes above motor block
autonomic blockade in spinal anesthesia in relation to sensory block
autonomic block is 2-6 dermatomes above sensory block
sensory and ANS blockade in relation to motor block in epidural anesthesia
Sensory and ANS blockade are 2-4 dermatomes above motor block
No autonomic differential blockade with epidural anesthesia
sensory and ANS blockade in relation to motor block in epidural anesthesia
Sensory and ANS blockade are 2-4 dermatomes above motor block
No autonomic differential blockade with epidural anesthesia
Modified Bromage Scale
- 0 = no motor block
- 1 = patient can’t raise extended leg but can move legs and feet
- 2 = patient can’t raise extended leg or move knee but can move feet
- 3 = complete motor block (can’t move legs, knees, or feet)
evaluates lumbosacral motor block
Modified Bromage Scale
- 0 = no motor block
- 1 = patient can’t raise extended leg but can move legs and feet
- 2 = patient can’t raise extended leg or move knee but can move feet
- 3 = complete motor block (can’t move legs, knees, or feet)
evaluates lumbosacral motor block
most significant controllable factors affecting spinal block height
dose, baricity, and patient position
which typically causes a denser block - spinal or epidural
spinal
what structure must be traversed by epidural LAs and what is their primary target
LAs in epidural space must first diffuse through dural cuff before anesthetizing nerve roots
primary drug-related determinant of LA spread in epidural space
volume of LA administered
what type of nerve fiber is blocked first after spinal anesthetic
type B - preganglionic ANS fibers
function of A alpha peripheral nerves
skeletal muscle - motor
proprioception
function of A beta peripheral nerves
touch
pressure
function of A gamma peripheral nerves
skeletal muscle tone
function of A delta peripheral nerves
fast pain
temp
touch
function of C peripheral nerves
sympathetic: postganglionic ANS fibers
dorsal root: slow pain, temp, touch
peripheral nerve fibers responsible for slow pain
C fibers (dorsal root)
primary determinant of epidural block density
LA concentration
for a spinal, how many mL of 0.75% bupivacaine are required to produce a T10 block?
- 0.75% = 7.5 mg/mL
- T10 dose = 10-15 mg
- volume = 1.25-2 mL
spinal dose & onset of bupivacaine 0.5-0.75% (no dextrose)
T10 block = 10-15 mg
T4 = 12-20 mg
onset = 4-8 min
duration of spinal bupivacaine 0.5-0.75%
plain: 130-220 min
w/ epi: + 20-50%
dose, onset, & duration of spinal 2-chloroprocaine 3% (+/- dextrose)
T10 dose = 30-40 mg
T4 dose = 40-60 mg
onset = 2-4 min
duration = 40-90 min
primary determinant of epidural block height
LA volume
initial epidural dose
1-2 mL per segment to be blocked
“top up” epidural dose
50-75% of the initial dose
should be admin. before block recedes > 2 dermatomes
why will a given volume of LA achieve greater spread in thoracic region compared to lumbar
Volume of epidural space is smaller in thoracic compared to lumbar region
primary determinant of epidural block density
LA concentration
how is a “walking epidural” achieved in OB
using a low enough concentration that provides analgesia while preserving motor function
concentration, onset, & duration of epidural 2-chloroprocaine
concentration = 3%
onset = 5-15 min
duration = 30-90 min
concentration, onset, & duration of epidural lidocaine
concentration = 2%
onset = 10-20 min
duration = 60-120 min
concentration, onset, & duration of epidural bupivacaine
concentration = 0.0625-0.5%
onset = 15-20 min
duration = 160-220 min
ratio of mass of substance relative to its volume (mass/volume) varies inversely with temperature
density
density of a substance relative to density of reference substance
specific gravity
analogous to specific gravity, but ratio is density of LA solution to density of CSF
baricity
density of water vs CSF
water = 0.9933
CSF = 1.003
Specific gravity of water vs CSF
water = 1
CSF = 1.002-1.009
baricity of water vs CSF
water = 0.9930
CSF = 1
describes the density of LA solution relative to CSF
baricity
baricity of isobaric LA solution
similar to CSF
Remains in place
As a general rule, solutions in saline are isobaric
Exception: procaine 10% in water 10% solution contains a lot of molecules, making it hyperbaric
baricity of hyperbaric solution
- LA solution with higher density than CSF
- Baricity > 1
- Solution will sink
what LA additive increases baricity
dextrose
LA solution with lesser density than CSF
hypobaric
baricity < 1
solutions that are hypobaric as a general rule
solutions in water
*Exception: procaine 10% in water - 10% solution contains a lot of molecules, making it hyperbaric
what happens to a hypobaric solution
will rise
highest points of lordosis in supine position
C5 and L3
highest points of kyphosis in supine position
T5-T7 and S2
for a spinal, how many mL of 3% 2-chloroprocaine required to produce a T4 block?
- 3% 2-chloroprocaine = 30 mg/mL
- T4 dose = 40-60 mg
- volume to give = 1.33-2 mL
in sitting position, how will a hypobaric solution spread in intrathecal space
towards brain
in supine position, how will hypobaric solution spread in intrathecal space
concentrate in lower lumbar region
after admin. a hyperbaric solution, the block is not as high as you expected. what can you do?
if block hasn’t already set, can place pt in T-burg
what happens after hyperbaric solution given if pt keeps sitting after block
solution will sink and anesthetize sacral nerve roots (saddle block)
what happens after admin hyperbaric solution if we lay pt supine after block
solution will slide down lumbar lordosis and eventually pool in sacrum & thoracic kyphosis
where does spinal anesthetic tend to level off
T4
what happens if If the patient becomes hypotensive immediately after SAB with hyperbaric solution and pt placed in Trendelenburg
the highest point of kyphosis shifts to T1 & creates possibility of high spinal
when is it safe to change positions after giving hyperbaric spinal solution
once the block is “set”
why does hypobaric solution not float towards cervical region if supine after spinal block
this would require LA to sink into thoracic kyphosis
what spinal levels give rise to cardioaccelerator fibers
T1-T4
what reflex contributes to asystole in spinal anesthesia
Bezold Jarisch reflex
slows heart to allow refill time
what reflex contributes to asystole in spinal anesthesia
Bezold Jarisch reflex
slows heart to allow refill time
Primary mechanism of hypotension with neuraxial anesthesia
anesthetic blockade of pre-ganglionic B fibers in sympathetic chain (sympathectomy)
Also ↓ catecholamine output from adrenal glands, skeletal muscle paralysis, direct effects of LAs that diffuse into systemic circulation
Primary mechanism of hypotension with neuraxial anesthesia
anesthetic blockade of pre-ganglionic B fibers in sympathetic chain (sympathectomy)
Also ↓ catecholamine output from adrenal glands, skeletal muscle paralysis, direct effects of LAs that diffuse into systemic circulation
Complications assoc with hypotension from neuraxial block
- N/V, impaired organ perfusion (heart/brain/gut), CV collapse
- In pregnant patients, impaired placental perfusion puts fetus at risk of ischemia & acidosis
how does neuraxial anesthesia affect preload
decreases
sympathectomy = complete dilation of venous circulation = blood pools in periphery = decreased venous return = decreased preload
how does neuraxial anesthesia affect afterload
decreased
Sympathectomy = partial dilation of arterial circulation
how does neuraxial anesthesia affect afterload
decreased
Sympathectomy = partial dilation of arterial circulation
SVR changes with neuraxial anesthesia in healthy pts vs. elderly pts with CV disease
healthy = decreases ~15%
elderly = decreases ~25%
how is CO affected by neuraxial anesthesia
variable
* dec VR = dec SV = dec CO
* dec SVR = dec CO
how is HR affected by neuraxial anesthesia
increased or decreased
* inc: hypotension = baroreceptor reflex activated
* dec: cardioaccelarator fibers blocked = inc PNS tone, Bezold Jarish reflex
how does a spinal to T4 affect Vm in healthy patients
negligible effect
most likely cause of apnea with spinal anesthesia
brainstem hypoperfusion
likely mediators of Bezold Jarisch Reflex
5-HT3 receptors in vagus n. & ventricular myocardium
how does neuraxial anesthesia affect accessory muscles
reduced function
Impaired intercostal muscles (inspiration & expiration
how does neuraxial anesthesia affect accessory muscles
reduced function
Impaired intercostal muscles (inspiration & expiration
how does neuraxial anesthesia affect accessory muscles
reduced function
Impaired intercostal muscles (inspiration & expiration
why might pt c/o dyspnea with neuraxial anesthesia
Loss of proprioception from chest
how can neuraxial anesthesia cause drowsiness
↓ sensory output to RAS
how does neuraxial anesthesia affect neuroendocrine stress response
By inhibiting afferent traffic from surgical site, neuraxial anesthesia ↓ surgical stress response
also↓ circulating catecholamines, renin, angiotensin, glucose, TSH, and growth hormone
how does neuraxial anesthesia affect neuroendocrine stress response
By inhibiting afferent traffic from surgical site, neuraxial anesthesia ↓ surgical stress response
also↓ circulating catecholamines, renin, angiotensin, glucose, TSH, and growth hormone
how does spinal anesthesia affect hepatic blood flow
not affected as long as systemic BP is maintained
GI effects of neuraxial anesthesia
- inhibit SNS tone, which ↑ PNS tone to gut
- Sphincters relax, peristalsis ↑
MOA of neuraxial opioids
Inhibit afferent pain transmission in substantia gelatinosa (lamina 2 of dorsal horn)
exerts analgesic effect by binding to mu receptors in substantia gelatinosa of dorsal horn
effect of neuraxial opioids combined with LAs
denser block
3 things neuraxial opioids do NOT cause
- sympathectomy
- skeletal muscle weakness
- changes in proprioception
3 directions opioid in intrathecal space can travel
- diffuse into spinal cord
- diffuse. outof intrathecal space
- ascend intrathecal space (rostral spread)
ranking opioids from most to least lipophilic
Sufentanil > fentanyl > meperidine > hydromorphone > morphine
Sexy Fathers Make Happy Mothers
ranking opioids from most to least lipophilic
Sufentanil > fentanyl > meperidine > hydromorphone > morphine
Sexy Fathers Make Happy Mothers
how do hydrophilic vs. lipophilic drugs tend to behave in the CSF
- Lipophilic drugs tend to leave CSF early
- Hydrophilic drugs tend to remain in CSF longer
The longer the drug remains in CSF, the more it spreads in intrathecal space and more likely it is to reach the brainstem
which tends. toproduce a more narrow band of neuraxial analgesia - fentanyl or morphine
fentanyl (more lipophilic)
onset of neuraxial fentanyl vs morphine
fentanyl: 5-10 min
morphine: 30-60 min
duration of neuraxial morphine vs. fentanyl
fentanyl: 2-4 hours
morphine: 6-24 hours
respiratory depression with hydrophilic vs. lipophilic neuraxial opioids
- lipophilic (fentanyl): early only
- hydrophilic (morphine): early + late
early < 6h, late > 6 h
diffusion of neuraxial opioids deposited into intrathecal vs. epidural space
intrathecal space - can easily diffuse into spinal cord
epidural space - diffuse within epidural tissue
why is a higher dose of neuraxial opioid required for epidural opioids
only a fraction reaches the subarachnoid space
sufentanil:
* intrathecal dose
* epidural dose
* epidural infusion
- intrathecal dose: 5-10 mcg
- epidural dose: 25-50 mcg
- epidural infusion: 10-20 mcg/hr
fentanyl:
* intrathecal dose
* epidural dose
* epidural infusion
- intrathecal dose: 10-20 mcg
- epidural dose: 50-100 mcg
- epidural infusion: 25-100 mcg/hr
hydromorphone:
* intrathecal dose
* epidural dose
* epidural infusion
- intrathecal dose: N/A
- epidural dose: 0.5-1 mg
- epidural infusion: 0.1-0.2 mg/hr
meperidine:
* intrathecal dose
* epidural dose
* epidural infusion
- intrathecal dose: 10 mg
- epidural dose: 25-50 mg
- epidural infusion: 10-60 mg/hr
morphine:
* intrathecal dose
* epidural dose
* epidural infusion
- intrathecal dose: 0.25-0.3 mg
- epidural dose: 2-5 mg
- epidural infusion: 0.1-1 mg/hr
4 key side effects of neuraxial opioids
- Pruritis
- Respiratory depression
- Urinary retention
- N/V
most common side effect of neuraxial opioids
pruritis
neuraxial opioid SE that’s most common in OB patients
pruritis
MOA of pruritis with neuraxial opioids
Likely caused by stimulation of opioid receptors in trigeminal nucleus or some other type of opioid-triggered neural process
management of pruritis with neuraxial opioids
- Can be treated with opioid antagonist like naloxone
- Diphenhydramine doesn’t fix the cause but sedative effects may be beneficial
what causes early respiratory depression from neuraxial opioids
systemic absorption
(occurs in < 6 h)
what causes late respiratory depression with neuraxial opioids
results from tendency to ascend towards brainstem, where they can inhibit respiratory center (occurs between 6-12 hours)
6 factors that increase resp depression with neuraxial opioid use
- high opioid doses
- co-administered sedatives
- low lipid solubility
- advanced age
- opioid naivety
- increased intrathoracic pressure
SE of neuraxial opioids most common in young males
urinary retention
MOA of urinary retention with neuraxial opioids
inhibition of sacral PNS tone causes bladder detrusor muscle relaxation & urinary sphincter contraction
Can be reversed with naloxone
MOA of N/V with neuraxial opioids
activation of opioid receptors in area postrema of medulla & vestibular apparatus
neuraxial opioid that can reactivate HSV type 1 in OB & postpartum pts
epidural morphine
Usually presents 2-5 days after admin.
MOA of HSV1 reactivation by epidural morphine
Best explained by cephalad spread of morphine to trigeminal nucleus
neuraxial LA that decreases efficacy of epidural opioids
2-chloroprocaine
neuraxial opioid most assoc. with sedation
sufentanil
how do neuraxial opioids affect peristalsis
slows, increasing gastric transit time
(opposite effect caused by neuraxial LAs)
how do neuraxial opioids cause an antidiuretic effect
increasing vasopressin release
how does epidural opioid admin affect breast milk
Minimal transfer of opioids from epidural space to breast milk
A = transverse process
B = superior articular process
C = lamina
D = spinous process
