neuraxial opioids Flashcards
outside the dura, can have a sensory block - a motor block - or both
epidural anesthesia
directly in CSF - quick side of effect
subarachnoid
what is the point of ERAS protocols?
to decrease amount of opioids being used by moving towards multimodal administration of meds
what is receptor distribution in spinal cord
All three (mu, kappa, delta) are present in high concentrations in the dorsal horn of the spinal concentrations in the dorsal horn of the spinal Cord -gelatinosa mainky mu
where else are mu receptors found in spinal?
substantia gelatinosa
a grey matter structure of the dorsal spinal cord primarily involved in the transmission and modulation of pain, temperature, and touch
substantia gelatinosa
what requires a higher dose of neuroaxial opioids?
epidural dose 5-10X subarachnoid dose
dose of morphine epidural vs subarachnoid:
epidural dose up to 5 mg
- spinal dose 0.25 – 1 mg
what type of pain are neuroaxial opioids best for?
visceral (organ) pain
MOA of Opioids placed in the epidural space
diffuse
across the dura to affect mu receptors on
the spinal cord AND are absorbed to
produce the effects like IV opioids
what opioid has slower onset in epidural space and why?
morphine because of lower lipid solubility so will have an increase in duration
what opioids will absorb more systematically?
fentanyl and sufentanil r/t higher lipid solubility
Fentanyl – CSF peak concentration
20 mins
Sufentanil – CSF peak concentration
6 mins
Morphine – CSF peak concentration
1-4 hours
what % of morphine epidural dose enters CSF?
3%
how are epidural opioids absorbed?
via the extensive venous plexus
in the epidural space
Fentanyl – peak blood conc epidural administration
5-10 mins
Sufentanil - peak blood conc epidural admin
<5 mins
Morphine - peak blood conc epidural admin
10-15 mins
how can absorption be decreased with epidural opioids?
add epinephrine to mixture: the epi vasoconstricts the venous plexus
does epinephrine affect the diffusion across the dura?
NO
what happens when epinephrine and morphine is injected into subarachnoid space?
the analgesia is enhanced compared to injection
of morphine alone.
duration of epidural fent?
50-100 mcg – lasts 1-3 hours
duration of epidural morphine
2-5 mg – lasts 4-24 hours
this is scary bc SE could last this long!
how does Higher lipid solubility affect mvmt of opioids in epidural space?
limits the movement cephalad as the
drug is taken up by the spinal cord
how does lower lipid solubility affect mvmt of opioids in epidural space?
allows longer
time in the CSF and movement cephalad
(think morphine)
what two things effect mvt of epidural opioids cephalad?
coughing and increase in pressure (straining)
NOT BODY MVMT
4 classic side effects of neuroaxial opioids?
pruritus
nausea and vomiting
urinary retention
Resp depression
most COMMON side effect of neuraxial opioids?
pruritis
MOA of pruritis with neuraxial opioids
Likely due to opioids in CSF moving up to interact with OR in the trigeminal nucleus
what type of patients does pruritis affect more and why?
OB pts due to estrogen
treatment of pruritis? (3)
-Opioid antagonist like Narcan
– Antihistamines
– Gabapentin
type of patients that urinary incontinence is more prevelant?
young males
what is urinary retention caused by?
interaction of opioid with opioid
receptors of the sacral spinal cord
inhibition of sacral parasympathetic outflow causing
detrusor muscle relaxation, increased bladder capacity
treatment of urinary retention?
narcan
With epidural morphine, how long can urinary retention last?
15 mins of admin to 16 hrs
describe the onset of ventilatory depression with neuraxial morphine
unpredictable and delayed - may be within minutes or 6-12 hours after
affects receptors in ventral medulla
describe onset of ventilatory depression with neuraxial fent and sufent
within 2 hours due to systemic absorption more than cephalad movement of opioid
risk factors for ventilation depression? (6)
– Larger dosages – Geriatric age – Receiving other opioids or sedatives – Prolonged or extensive surgery – Presence of co-morbidities – Thoracic surgery
2 things that cause an Increased risk of delayed depression
– Patient also receiving IV opioid or sedative
– Patient coughing to move opioid cephalad
what pt population does vent depression affect least
OB bc of progesterone !!!!
what is Most reliable sign of ventilatory depression and why?
decreased LOC bc pao2 late sign
treatment of vent depression?
narcan 0.25 mcg/kg/hr (maybe)
what neuraxial opioid is most r/t to sedation
sufent
explain the MOA of CNS excitation from neuraxial opioid (rare)
cephalad migration of opioid in CSF
and interaction with non-opioid receptors in
the brainstem or basal ganglia
what two neurotransmitters can opioids potentially block inhibition
GABA and glycine (meaning there is more)
what virus is reactivated by neuraxial morphine 2-5 days after admin?
herpes due to trigeminal nucleus interaction
will you see vent depression in neonate?
YES
Related to systemic absorption of opioid
–– Minimal opioid found in breast milk
Don’t withhold analgesics from C-section patients
what can neuraxial opioids do to the eyeballs
Miosis, nystagmus, vertigo
other side effects of neuraxial opioids?
- delayed gastric emptying
- decreased body temp
- water retention (vaso)
