Transcript Neuraxial Opioid-Induced Pruritus: A Review

Neuraxial Opioid-Induced
Pruritus
Tariq Alzahrani
Demonstrator
College of Medicine
King Saud University
Definition
Is a sensation that provokes the desire to
scratch & can be aroused by variety of
mechanical, electrical & chemical stimuli.
 It is bothersome to the patient &
sometimes may be more unpleasant
than pain itself for the patient.

Incidence
It is varies from 30% to 100%.
 Parturients appear to be the most
susceptible, reported between 60% &
100% & appears to be dose-dependent.
This increased incidence may be due to
an an interaction of estrogen with opioid
receptors.
 In orthopedic surgery between 30% &
60%

Pathophysiology
The sensation of itch arises from the
superficial layers of the skin, the mucous
membranes & the conjuctivae.
 Based on microstimulation studies, the
current view is that nerve endings in the
subepidermal area cluster densely
around itch points that correspond to
areas that are very sensitive to
pruritogenic stimuli in humans.

Postulated the C fiber may represent the
afferent units mediating itch sensation.
 The exact mechanism of neuraxial
opioid-induced pruritus is unclear.

 Postulated
mechanisms include :
-The presence of an itch center in the
CNS
-Medullary dorsal horn activation
-Antagonism of inhibitory transmitters
-Modulation of the serotoninergic pathway
-Involvement of prostaglandins
The presence of an itch center in the
CNS
Koenigstein has described the presence
of an itch center in the lower medulla that
includes the trigeminal nucleus.
 Injection of high doses of morphine(0.2
to 1mg/kg) into the cisterna
cerebellomedullaris of cats induced itch
behavior.
 Intracisternal injection of alizarin blue
produced itch & stains in depth only the
lower part of the medulla oblongata.

Antagonism of inhibitory
neurotransmitters
Opioid antagonism of GABA & glycine in
the CNS .
 Intrathecal administration of the glycine
antagonist strychnine in cats produces
similar itch & scratch behavior as large
doses of intrathecal morphine.

Medullary dorsal horn activation &
serotonin

Morphine produces part of its analgesic effect
through the release of serotonin.
 There are dense concentration of serotonin
receptors in the dorsal part of spinal cord & the
nucleus of spinal tract of the trigeminal nerve
in the medulla, in which opioid receptor density
is also high.
 These observations suggest that the 5-HT
receptor may be implicated in the development
of the pruritus associated with neuraxial
opioid.
Prostaglandins
PGE1 & PGE2 enhance C fiber
transmission to the CNS.
 They are also known to release
histamine & to potentiate pruritus
induced by histamine.


Co-administration of epinephrine may
have an influence on spinal & epidural
opioid-induced pruritus.
Prevention & Treatment
Pharmacologic agent
Mechanism
Site of action
Opioid antagonist
Mue-receptor inhibition
Medullary dorsal horn,
nucleus trigeminalis
Propofol
Depression of nerve
transmission
Medullary dorsal horn
NSAIDs
Cyclooxygenase enzyme Endoplasmatic reticulum
inhibition
of macrophages
Droperidol
Depression of nerve
transmission
5-HT3 receptor inhibition
Medullary dorsal horn,
nucleus trigeminalis
5-HT3 antagonist
5-HT3 receptor inhibition
Medullary dorsal horn,
nucleus trigeminalis
Conclusion
Although pruritus after neuraxial
administration of opioids is a common
side effect, to date few studies have
elucidated the mechanisms, mediators,
neural pathways & pathophysiology of
this symptom.
 A better understanding of the
pathophysiology would lead to improved
preventative & treatment strategies.


In the management of neuraxial opioidinduced pruritus we recommend that
minimal analgesic doses of opioids
should be used to provide pain relief
during & after surgical operation.
5-HT3 receptor antagonists
(ondansetron) the drug of choice due to :
-Minimal side effects ( headach )
-No effect on the quality of analgesia
-Ability to prevent & treat potoperative
nausea & vomiting
 With multiple pathways involved in the
pathophysiology of pruritus, combination
therapy should be examined.
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