Chapter 30 Intrathecal Opioid Injections for Postoperative Pain Flashcards Preview

Essentials of Pain Medicine > Chapter 30 Intrathecal Opioid Injections for Postoperative Pain > Flashcards

Flashcards in Chapter 30 Intrathecal Opioid Injections for Postoperative Pain Deck (43):

Common uses
of IT opioids for postoperative analgesia

obstetric and gynecologic surgery, orthopedic joint and spine procedures,
thoracic and vascular procedures, cardiac bypass, pediatric surgery, urologic procedures, and abdominal procedures.


Fibers that play a major role in the transmission of pain

Nociceptive information is transmitted by multiple afferent
neurons with small-diameter unmyelinated and thinly
myelinated fibers (C-fibers and Ad-fibers, respectively)


Central terminals of small unmyelinated fibers are located in

Rexed’s laminae I, II, and III


What provides the anatomic basis for selective analgesia by opioids injected into the cerebrospinal fluid (CSF)

Opioid receptors exist in
Rexed’s laminae I, II, and V in the dorsal horn of the spinal cord.


Spinal cord analgesia is likely mediated by what receptors?

mu- and k-receptors.


substance P

substance P is released into the CSF by electrical stimulation. This release is inhibited by the administration of morphine
into the CSF and possibly mediated by gammaaminobutyric
acid (GABA) presynaptically and glycine postsynaptically



Lipophilicity (versus hydrophilicity) is the key property affecting the speed of onset and duration of action. Highly lipid-soluble drugs such as fentanyl and
sufentanil have a faster onset but shorter duration of action when used intrathecally


Highly lipid-soluble drugs have shorter duration of action when used intrathecally

Shortly after injection,
CSF levels are barely detectible as the drug is quickly distributed to the spinal cord. This may result in a more
segmental spread of analgesia and a lower concentration reaching the brain, decreasing the risk of delayed respiratory
depression (e.g., 12 to 24 hr after injection)


Hydrophilic opioids

Hydrophilic opioids, such as morphine, have a slower onset and longer duration of action, and remain detectable
in the CSF long after injection. Delayed respiratory depression may be more likely with morphine than other
lipophilic drugs, as morphine remains in the CSF long enough to circulate rostrally to the brainstem and respiratory


Only opioid has strong enough local anesthetic
properties to be used as a sole agent for surgery.

meperidine. IT injection of meperidine produces spinal anesthesia that
is qualitatively similar to that achieved with conventional local anesthetics.


Why can meperidine be used as the sole agent in
spinal anesthesia?

It is likely the combined action of its local anesthetic properties and its opioid receptor binding


meperidine vs. fentanyl

The onset of action for meperidine is similar to that of fentanyl despite being significantly less
lipid soluble; however, its duration is longer than fentanyl


meperidine vs. morphine

Meperidine has a shorter duration of action than
morphine, as meperidine dissipates from the CSF four times faster than morphine.


IT opioids dose vs. IV or epidural

Equianalgesic doses
of IT opioids are typically a small fraction of those used for intravenous or epidural use


The duration of analgesia for a hydrophilic opioid compared to IV or epidural

The duration of analgesia for a hydrophilic opioid
such as morphine is greater compared to intravenous or
epidural administration


A single IT injection of morphine 0.04 to 0.5 mg will provide analgesia up to

15 to 24 hr of analgesia.


hemodynamic changes of opioids when
applied intrathecally

Unlike neuraxially administered local anesthetics, which
may result in vasodilation and hypotension, opioids do not per se cause adverse hemodynamic changes when applied intrathecally and may not significantly attenuate
the neuroendocrine stress response even when administered
in extremely large doses (4.0 mg)


effect of opioids on motor blockade or sensory

opioids do not cause motor blockade or sensory loss,
potentially allowing earlier ambulation


benefit of IT opioids when used with local anesthetics

IT opioids do provide a sparing effect for local anesthetics, allowing lower doses to be used intrathecally or epidurally while still maintaining adequate analgesia



most feared complications are respiratory depression
and arrest


Respiratory depression typically occurs when

within minutes to hours for the lipophilic opioids (fentanyl, sufentanil) with early respiratory depression (minutes) not being reported with a hydrophilic opioid such as morphine


Common Side Effects of Intrathecal Opioids

Mild respiratory depression
Urinary retention


Uncommon Side Effects of Intrathecal Opioids

Respiratory arrest
Generalized muscle rigidity
Epileptic seizure
Water retention


The risk of respiratory depression increases with

the addition of systemic opioids or sedatives, increasing age, lack of opioid tolerance (i.e., opioid-naive state), obesity, and sleep apnea


mechanism of hydrophilic opioids causing respiratory

the migration of opioid
within the CSF to and reaction with opioid receptors in
the ventral medulla


treatment of respiratory
depression due to opioids

Naloxone has been used effectively
to treat respiratory depression from IT opioids,



Oil–Water Partition
Coefficient*: 1.4
Typical Adult
Intrathecal Dose: 0.05- 0.6mg
Onset of Analgesia
(minutes): 30-60
Duration of Analgesia
(minutes: 480-1440



Oil–Water Partition
Coefficient*: 39
Typical Adult
Intrathecal Dose: 10-100mg
Onset of Analgesia
(minutes) : 2-12
Duration of Analgesia
(minutes: 60-400



Oil–Water Partition
Coefficient: 816
Typical Adult
Intrathecal Dose: 10-50mcg
Onset of Analgesia
(minutes) : 5-10
Duration of Analgesia
(minutes): 30-120



Oil–Water Partition
Coefficient: 1727
Typical Adult
Intrathecal Dose: 2.5- 12.5mcg
Onset of Analgesia
(minutes): 3-6
Duration of Analgesia
(minutes: 60-180


Advantages of Intrathecal Opioids

Long duration of action
Small doses required for equianalgesic effect
Almost undetectable vascular absorption
Ease of cannulating the intrathecal space
Minimal hemodynamic changes
No motor blockade
No sensory loss


IT opioid-induced
pruritus is likely due to

cephalad migration of the drug and interaction with opioid receptors in the trigeminal nucleus located superficially in the medulla, the exact etiology is not clear. Itching does not appear to be histamine mediated
nor is it related to systemic absorption of the drug. Antihistamines are minimally effective as a treatment;


IT opioid-induced
pruritus treatment

Opioid receptor antagonists, such as
naloxone, and opioid agonists–antagonists are effective in the treatment for pruritus. Low-dose intravenous naloxone may be effective in attenuating pruritus
but does not generally decrease the analgesic efficacy of IT opioids


unconventional IT opioid-induced pruritus treatment

Propofol in a 2-mg dose may relieve pruritus without affecting analgesia, but is less effective than μ receptor antagonists. Ondansetron may be an effective agent for treating spinal or epidural morphine induced pruritus. Prophylactic ondansetron 0.1 mg/kg
intravenous (IV) has also been shown to reduce the incidence of pruritus after IT morphine


The presumed mechanism of IT opioid-induced n/v

the cephalad migration of drug and subsequent interaction
with opioid receptors in the area postrema


Treatment of IT opioid-induced n/v

Naloxone is generally effective in the treatment of nausea and vomiting induced by IT opioids. Long-acting opioid antagonists may not be as
effective in treating nausea, but there may be a benefit if given prophylactically.


mechanism of IT opioid-induced Urinary retention

related to opioid receptor–induced inhibition of sacral
parasympathetic nervous system outflow, resulting in detrusor relaxation and an increase in bladder capacity


Treatment of IT opioid-induced Urinary retention

Naloxone may be effective in treatment, although bladder
catheterization is frequently required


Relationship between IT morphine and Herpes

Herpes simplex labialis virus reactivation has been reported following IT morphine. Epidural
morphine has also been postulated to cause reactivation of herpes. Opioids reach the sensory ganglia where the herpes virus lies dormant and may reactivate the virus
through an unknown interaction


IT Sufentanil for Postop Analgesia

Sufentanil (10 mg) improves and prolongs the duration of surgical
analgesia in patients undergoing cesarean section but at the cost of increased hypotension and pruritus


IT morphine doses

IT morphine is clearly beneficial in reducing additional opioid requirements in patients undergoing
orthopedic surgery, but the optimal dose is not clear.
For patients who are opioid-tolerant, higher doses are probably acceptable while doses of less than 0.3 mg may be ideal for opioid-naive individuals


pediatric patients IT morphine doses

in pediatric patients,
IT morphine in doses less than 10 mg/kg has been demonstrated
to be effective in children 6 months of age
or older



Clonidine, an alpha-2 receptor agonist, has been used to improve analgesia in combination with IT opioids as
well as with IT local anesthetics. Clonidine increases the
duration of sensory and motor blockade from bupivicaine
spinal anesthesia through several mechanisms. Alpha-2
adrenergic agonists administered intrathecally may increase the antinociceptive threshold by activating descending noradrenergic pathways in the spinal cord

Decks in Essentials of Pain Medicine Class (80):