pain and analgesia Flashcards
what is pain?
Pain is a subjective experience
Sensory discriminative: Location, intensity, threshold
experience associated with, or resembling that associated with actual or potential tissue damage (IASP, 2020)
important alert system
what is acute pain
examples
< 12 weeks
Acute pain is a protective mechanism
broken bones
surgery
dental work
labor and childbirth
cuts
burns
- to ensure healing
how can you rate pain
Numeric Rating Scale
Visual Analog Scale (VAS)
Verbal Pain Intensity Scale
(young/disabled patients
functional scale
0 = no pain
1 = tolerable and pain does not prevent any activities
2 = tolerable and pain prevents some activities
3 = intolerable and pain does not prevent use of telephone, TV viewing or reading
4 = intolerable and pain prevents use of telephone, TV viewing or reading
5 = intolerable and pain prevents verbal communication
what is chronic pain
“Pain in one or more anatomic regions that persists or recurs for longer than three months and is associated with significant emotional distress or significant functional disability”
types of chronic pain?
Nociceptive/Inflammatory
e.g., osteoarthritis, post-operative pain,
rheumatoid arthritis
Neuropathic
e.g., nerve injury,
multiple sclerosis, stroke, amputation, neuropathies
Nociplastic
e.g., fibromyalgia,
irritable bowel syndrome
what is NOCICEPTIVE / INFLAMMATORY PAIN
examples
- tissue injury
Aches and sprains (back pain)
Arthritis
Cancer pain
Post-operative pain
Headache
Nociceptive pain may be
acute : lasting < 3 months, desirable defence mechanism
chronic : lasting >3 months, undesirable, lack of warning function, beyond normal healing
what is Allodynia
Pain after stimulation which is not normally painful
what is Hyperalgesia
Increased pain from a stimulus that normally provokes pain.
what is NEUROPATHIC PAIN
examples
Damage to peripheral (neuralgia, neuropathy due to injury or infection) or central (trauma, stroke, MS) nerves
Neuropathic pain can be intermittent or constant, and spontaneous or provoked.
Neuropathic pain may be described as:
severe, sharp, burning, cold, producing numbness, tingling or weakness.
Neuropathic pain is a major health problem that affects a significant number of patients, resulting in personal suffering, reduced productivity and substantial health care costs.
Diabetic neuropathy
Phantom limb pain
Cancer pain
Chemotherapy-induced peripheral neuropathy
Postherpetic neuralgia
NOCIPLASTIC PAIN
Mechanisms not entirely understood
”Pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain” (IASP, 2017)
Patients can have a combination of nociceptive and nociplastic pain
Observed symptoms:
multifocal pain that is more widespread or intense, or both;
fatigue, sleep, memory, and mood problems.
Fibromyalgia,
Complex regional pain syndrome type 1,
Irritable bowel syndrome
what is chronic pain
Pain that persists past normal healing time: post surgical pain; migraine.
It lasts or recurs for longer than 3 months.
pain control mechanism (treatment options)
acute treatment
preventive treatment
Acute treatment: symptoms of pain (e.g., anti-inflammatory to stop a single headache attack, opioid to reduce post-surgical pain)
Preventive treatment: underlying disorder (e.g.; mirror therapy in phantom limb syndrome
Aspirin and other NSAIDS
Morphine and other opioid/cannabinoids
diff between chronic secondary pain and chronic primary pain
both can last over 3 months
can happen together
Chronic Primary Pain
Widespread Pain (fibromyalgia)
Complex regional pain syndrome
Primary headache
Irritable Bowel syndrome
Musculoskeletal pain
(nonspecific low-back pain)
Chronic Secondary Pain
Cancer Pain
Post surgical Pain
Visceral Pain
Neuropathic pain
Headache and orofacial pain
Nociceptive pathway
1.Detection of pain in the periphery.
Noxious stimuli (to skin or subcutaneous tissue) activates nociceptors
- Transmission of pain signals from the periphery to spinal cord,
Signals are amplified or inhibited by local neuronal circuits and descending inhibitory
pathways from higher brain centers - Reception of signal by higher central brain centers,
afferent activity generates a pain sensation and initiates an appropriate response
Peripheral nerves contain small and large diameter ‘primary afferent’ fibers
what are there names (3) what is the use?
Medium diameter MYELINATEDfibers (Ad) mediates acute, well-localised or fast pain
Small diameter UNMYELINATEDfibers (C),convey poor localised or slow pain
Large diameter MYELINATED fibers (Non-nociceptive) (Ab) Touch, pressure
Unmyelinated and small myelinated fibers only respond to noxious (‘painful’) stimulation
But in the setting of tissue injury, these nerve fibers will respond to innocuous stimuli
NON-PAINFUL STIMULI HURT!
what are the Inflammatory mediators of peripheral pain
- Bradykinin (produced from precursors in the vasculature) activates
B2 receptors in nociceptive neurones
B1 receptors: via the metabolite des-Arg9BK; ‘upregulated’ by inflammation - Substance P: activate NKA (neurokinin) receptors in nociceptive neurones
- Adenosine triphosphate (ATP): activate P2X3 receptors
- Protons (H+): activate Acid-Sensing Ion Channels (ASICs)
- Prostaglandins, in particular, PGE2 and PGF2 released in inflammation, greatly increase responses to bradykinin and 5-HT = sensitization
what are prostanoids?
Prostanoids (prostaglandins and thromboxane) produced from precursors in cell membrane
In particular, PGE2 and PGF2 released in inflammation, greatly increase responses to bradykinin and 5-HT
= sensitization
Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) such as aspirin block the cyclooxygenase enzyme
what are the important neurotransmitters -
Nociceptive pain is due to excessive peripheral stimulation;
inflammatory mediators cause hyperalgesia
1) Glutamate (excitatory amino acid) acts at:
AMPA receptors mediate acute pain (fast response, sets baseline)
NMDA receptors (delayed response)
2) Substance P (peptide) acts at NK1 (NKA) receptors to enhance NMDA action (hypersensitivity). Often CGRP (peptide) is co-released; leading to…..
3) Nitric oxide (NO) release which enhances further transmission of pain signal (hyperalgesia)
what can be given for pain therapy?
Nociceptive pain: non-opioid (paracetamol, aspirin and other Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)) and opioid analgesics are the main drugs used to treat pain.
Non-opioids are limited by ceiling effect (dose above which there is no further pharmacological action)
what are the Pain therapy: non-opioid drugs
COX - inhibitors
- aspirin
-ibuprofen
what is cox-1 and 2
COX-1
Constitutive enzyme
Expressed in most tissue
‘housekeeping’ role
COX-2
Inducible enzyme
Production of mediators of inflammation
when is NSAID used for pain therapy?
examples
Used for
acute mild to moderate pain
chronic disease accompanied by pain and inflammation
NSAIDs also widely used to prevent blood clots and as anti-pyretic (reduce fever) and anti-inflammatory agents
Aspirin (acetylsalicylic acid)
Used in headache, transient musculoskeletal pain, dysmenorrhoea (period pain) etc.
Non-selective NSAIDs:
Indoles: diclofenac or indomethacin
Propionic acid derivatives: ibuprofen, naproxen and ketoprofen
when is NSAID used for pain therapy?
examples
Used for
acute mild to moderate pain
chronic disease accompanied by pain and inflammation
NSAIDs also widely used to prevent blood clots and as anti-pyretic (reduce fever) and anti-inflammatory agents
Aspirin (acetylsalicylic acid)
Used in headache, transient musculoskeletal pain, dysmenorrhoea (period pain) etc.
Non-selective NSAIDs:
Indoles: diclofenac or indomethacin
Propionic acid derivatives: ibuprofen, naproxen and ketoprofen
