Transduction
detect noxious stimuli
Transmission
from noxious stimuli to brain
Perception
how the brain interprets pain
Modulation
descending inhibition of nociception through the release of NT
What is acute pain and how long does it last?
from tissue injure and resolves when it heals
less than 3 months
How long does pain have to last before it becomes chronic pain and is acute pain treatment effective for chronic pain?
greater than 3 months
NO
Poorly controlled acute pain can lead to peripheral and central changes that result in _______ ____
chronic pain
Neuronal plasticity
acute pain induced change in the CNS
Allodynia
painful response to a perviously non painful stimuli
Hyperalgesia
increased response to pain
What surgical procedure are most associated with chronic pain?
Amputation
Thoracotomy
Open inguinal hernia repair
Abdominal hysterectomy
Open cholecystectomy
Nephrectomy
Mastectomy
What is the goal of acute pain control?
block nociceptive pain
What are the 3 classes of acute pain?
Background
Breakthrough
Intermittent
What is preemptive analgesia?
blocking pain transmission prior to stimulus
What is preventative analgesia?
block development of sustained pain
What is the required criteria of preventative analgesia?
1. Adequate depth of analgesia blocking all nociceptive input
2. Analgesic technique adequate to block the entire surgical field
3. Analgesic duration includes surgical and post-surgical periods
What is multimodal analgesia
Combining a variety of medications and anesthesia techniques to improve synergistic actions of each method
How do opioids work on receptors in the periphery?
Receptors on primary afferents neurons inhibit release of substance P
How do opioids work on receptors in the dorsal horn?
Inhibit Ca presynaptic to reduce NT release
Enhance K efflux postsynaptic to hyperpolarize cell
Activate descending pathway to inhibit brainstem GABA
How do opioids work on receptors in the supraspinal area?
Receptors are in periaqueductal grey, nucleus raphe magnus, and rostral ventral medulla
What is opioid induced hyperalgesia (OIH)?
paradoxical response to opioids
increased sensitivity to pain after opioid administration
What drugs is OIH associated with?
high does phenanthrene opioids (Morphine)
Versed
How do you prevent OIH?
coadministration of NMDA antagonists (ketamine)
Change to phenyl piperdine (fentanyl)
Should meperidine (a phenylpiperdine opioid) be used for long term use?
No
What receptors does Methadone work on and what is it ideal for?
Mu agonist
NMDA antagonist
MOA inhibitor
neuropathic pain
What is COX 1 enzyme good for?
gastric protection/hemostasis
What is COX 2 enzyme good for?
prostaglandins that mediate pain, inflammation, and fever
How does Acetaminophen/Paracetamol act?
central inhibition of COX enzyme
Receports: opioid, cannabinoid, NMDA
What is NMDA activation associated with?
Persistent postoperative pain
Wind-up/Allodynia
OIH
Opioid tolerance
What are a few actions of Ketamine?
blocks NMDA and Na channels
Cholinergic (salivation)
Name 3 weak NMDA antagonists?
Memantine
Dextromethorphan
Methadone
MOA of a2-adrenergic agonists
-CNS pre-synaptic ?2 activation decreases release of NE
-Reduces sympathetic outflow which lowers BP
-Noradrenergic receptors cause sedation
-Modulate descending pain pathway (analgesia)
Spinal cord post-synaptic ?2 activation
-Dorsal horn (substantia gel
What are 2 a2-adrenergic agonists?
clonidine
dexmedetomidine
How does a2-adrenergic agonists help with peripheral and spinal nerve blockade?
inhibits a-delta and c-fiber transmission
What do Gabapentinoids prevent?
antihyperalgesic (NOT analgesic)
What are complications of regional anesthesia?
nerve damage
bleeding
incomplete block
What drugs work on transduction of pain?
LAs
capsaicin
anticonvulsants
NSAIDs
ASA
Acetaminophen
nitrate
What drugs work on the transmission of pain before the dorsal horn?
LA
opioids
What drugs work on the transmission of pain in the dorsal horn?
LA
a2-agonists
What drugs work on the perception of pain?
opioids
a2-agonists
TCA
SSRI
SNRI
What drugs work on the modulation of pain?
TCA
SSRI
SNRI
What pain level should be expected after surgery?
5
Persistent Post Surgical Pain (PPSP)
Defined as pain that persists beyond normal healing timeframe (1-2 months after surgery)
What surgeries have high risk of developing PPSP?*
Amputations
Breast surgeries
Inguinal hernia repair
Thoracotomy
What are risk factors for PPSP?
Higher pain sensitivity
Anxious
Catastrophizing
Suffering depression
What can peripheral nocioceptors become sensitized to?
mechanical, thermal, and chemical stimuli
What is the central mechanisms of chronic pain?
loss of segmental inhibition in dorsal horn
Wide Dynamic Range neurons
Reorganization of neural connections
Name the neurochemical mediators of peripheral sensitization
Histamine
Bradykinin
Prostaglandin
Substance P
Glutamate
How is TNF-A released after never damage associated with hyperalgesia?
decreases K conduction
What are neurochemical mediators of central sensitization?
Excitatory: glutamate, aspartate, sub P, neurokinin A
Inhibitory: glycine, GABA
Na channel dependent transmission is fast pain via ____ and _______ receptors.
AMPA
Kainate
Repeated c-fiber stimulation leads to secondary hyperalgesia (wind up) which leads to _______ _________
central sensitization
What is Facilitation?
The excitatory process by which a neurotransmitter released by one nerve causes the second nerve to release a greater than normal amount of neurotransmitter.
What drugs are used for cancer pain?
opioids with adjuncts
What drugs are used for neuropathic pain?
ANTIDEPRESSANTS*
anticonvulsants
What drug may be effective for fibromyalgia?
Tramadol
MOA of TCAs
block serotonin and NE reuptake
MOA of SNRI
block serotonin and NE receptors
When are TCAs (nortriptyline, amitriptyline, despramine) commonly used for chronic pain?
post herpatic neuropathy (shingles)
diabetic neuropathy
What's the benefit of SNRIs vs TCAs?
non sedating
What are SNRIs (venlafaxine, Duloxetine (Cymbalta), Milnacipran) the first line treatment for?
Diabetic peripheral neuropathy
What are the uses for Anticonvulsants in chronic pain?
Neuropathic pain syndromes- PHN, DPN and spinal cord injury, fibromyalgia
If a patient has paresthesia, should you give them a nerve block?
no
What are the radicular symptoms of herniated disc?
pain- sharp/shooting
paresthesias
numbness
weakness
What is the first choice treatment in herniate disc therapy?
NSAIDs
What are the s/s of spinal stenosis?
-Radicular pain radiates to buttocks, thighs & legs
-Worsens with activity
-Pseudo-claudication (impaired walking)
-Improves with rest and spine flexion ("shopping cart sign")
How is spinal stenosis diagnosed?
MRI
CT
Electromyography
What is the treatment for spinal stenosis?
epidural steroid injection (ESI)
minimally invasive lumbar decompression (MILD)
What is epidural steroid injection indicated for, when is it effective, when does benefit stop?
Symptomatic nerve root compression
Within 2 wks of onset of pain
After 3 months
What's the most effective approach for ESI?
transforaminal (medication placed at nerve root)
What are the S/S of facet joint pain?
Midline back pain
Radiating to buttocks, thigh and knee.
Worsens on hyperextension and lateral flexion
What is the treatment for facet joint pain?
Medial branch blocks
Facet joint injection
What symptom is associated with Sacroiliac joint Syndrome?
medial buttock pain
How is Sacroiliac join syndrome diagnosed?
FABER Patrick test - leg flexed and the thigh abducted and externally rotated
Gaenslen test - hip joint flexed with opposite hip extended
Yeoman and Gillet - supine and hyperextend the hip
Positive results to SI joint injection
How do you treat Sacroiliac Joint syndrome?
-SI joint injection w/ LA and steroid
-Denervation of L5 medial branch and S1-S3 lateral branch
What are the S/S of piriformis syndrome?
Pain with prolonged sitting
Aggravated by hip flexion/internal rotation
Sciatic nerve irritation
How is Piriformis syndrome diagnosed?
Pace sign - resisted adduction
Lasegue sign - leg flexion with adduction and internal rotation
Freiberg sign - forced internal rotation with leg extended
What is the treatment of Piriformis syndrome?
-muscle relaxants, anti-inflammatory, and analgesics
-Injection of LA +/- steroid / Botox
What is myofascial pain syndrome?
painful "trigger point" of taut band of muscle
spot tenderness
What is the treatment of myofascial pain syndrome?
Trigger point injection with LA
Dry needling
What are the symptoms of Fibromyalgia?
3 or more months of allodynia and tender points
Fatigue
Sleep disturbance
Cognitive dysfunction
What is the most common type of neuropathic pain?
Diabetic neuropathy
What neuropathy is associated with a "stocking glove" distribution?
Diabetic
How do you manage diabetic neuropathy?
correction of blood glucose
anticonvulsants
TCA
SNRI
Complex regional pain syndrome 1 and 2 have similar symptoms EXCEPT:
CRPS 2 has a known preceding nerve injury
What triggers complex regional pain syndrome and who is at greatest risk (male or female)?
triggered by surgery, fractures, trauma
Females
What are symptoms of complex regional pain syndrome?
hyperalgesia
sweating
skin color/temp changes
limb stiffness/tremors
How do you treat CRPS?
TENS
sympathetic blocks
NSAIDS
Gabapentin
NMDA antagonists
When do you see symptoms of Post herpatic neuralgia?
pain after herpes zoster skin erruptions
pain persists > 3 months
What causes phantom pain?
neuromas
c-fiber activity
Na channel activation
abnormal interneuron firing
New synaptic connections in cerebral cortex
Treatment for phantom pain
Epidural/Peripheral Nerve Blocks
Opioids
Gabapentin
NMDA antagonists
Antidepressants
TENS/SCS
What is the prophylactic therapy for headaches?
Beta blockers
Calcium Channel Blockers
Amitriptyline
Botox
In what cancer should opioids be reduced?
breast cancer