(PM3B) Pain & Analgesia Flashcards
What are the components of pain?
(1) Sensory
(2) Emotional
Hence why it is subjective
What are some different methods to rate pain?
(1) Numeric rating scale
- 1-10
- functional scale
(2) Visual analogue scale
- No pain to worst possible pain
(3) Verbal Pain Intensity Scale
- for young/ disabled patients
- no pain to unimaginable/ unspeakable pain
- also a 1-10 scale
What do the different numbers (1-5) of a functional pain scale correspond to?
0 = no pain
1 = tolerable + pain does not prevent activities
2 = tolerable + pain prevents some activities
3 = Intolerable + pain does not prevent use of phone/ TV/ reading
4 = Intolerable + pain prevents use of phone/ TV/ reading
5 = Intolerable + pain prevents verbal communication
What is the purpose of acute pain?
Protective mechanism
e.g. thermal burns
What are the types of pain?
(1) Nociceptive pain
(2) Neuropathic pain
What type of pain is caused by a tissue injury?
Nociceptive pain
How long does acute nociceptive pain last?
<3-6 months
Desirable
How long does chronic nociceptive pain last?
> 6 months
Undesirable
What is allodynia?
Pain after stimulation
Not normally painful
What is hyperalgesia?
Increased pain from a stimulus that normally causes pain
What is neuropathic pain?
Nerve injury
What are some conditions that are associated with neuropathic pain?
(1) Diabetic neuropathy
(2) Phantom limb pain
(3) Cancer pain
(4) Chemotherapy-induced peripheral neuropathy
(5) Postherapeutic neuralgia
How may neuropathic pain be described?
(1) Severe
(2) Sharp
(3) Burning
(4) Cold
(5) Numb
(6) Tingling
(7) Weakness
What is the pain pathway?
(1) Detection of pain in the periphery
(2) Transmission of pain signals from periphery to spinal cord
(3) Reception of signal by higher central brain centres
Describe the role of local neuronal circuits and descending inhibitory pathways from higher brain centres.
Signals are amplified or inhibited
Describe the myelination state of non-nociceptive Aß.
Myelinated
Describe the myelination state of nociceptive C.
Unmyelinated
What sensation do non-nociceptive Aß fibres produce?
Touch + pressure
What sensation do nociceptive C fibres produce?
Dull + burning pain
What sensation do nociceptive A-delta produce?
Sharp pain
What is the gate control theory of pain?
Melzack + Wall’s theory
Inhibitory interneurons in spinal cord control incoming sensory information before it’s transmitted to the brain
(1) Activation of C/ A-∂ fibres open gate (increased pain)
- direct excitation of gate OR inhibition of SG interneurons
(2) SG interneurons inhibit
- close the gate
- reduce pain
(3) Activation of Aß fibres close gate by excitation of Sg interneurons
(4) Descending inhibitory pathways from CNS close gate
- inhibit the gate OR direct activation of SG interneurons
What are some inflammatory mediators of peripheral pain?
(1) Bradykinin
(2) Substance P
(3) ATP
(4) Protons
(5) Prostaglandins
- particularly PGE2 + PGF2
What is the role of bradykinin as an inflammatory mediator of peripheral pain?
Activates B2 receptors in nociceptive neurones + B1 receptors via a metabolite
What is the role of substance P as an inflammatory mediator of peripheral pain?
Activates NKA (neurokinin) receptors in nociceptive neurones
What is the role of ATP as an inflammatory mediator of peripheral pain?
Activates P2X3 receptors
What is the role of protons (H+) as an inflammatory mediator of peripheral pain?
Activate acid-sensing ion channels (ASICs)
What is the role of prostaglandins as an inflammatory mediator of peripheral pain?
PGE2 + PGF2
Greatly increase responses to bradykinin and 5-HT
Increase sensitisation
What are prostanoids?
Prostaglandins + thromboxane
Produced from precursors in cell membrane
What are some important neurotransmitters in hyperalgesia?
(1) Glutamate
- acts at AMPA to mediate acute pain
- acts at NMDA receptors (delayed)
(2) Substance P
- acts at NK1 receptors
- enhances NMDA action (hypersensitivity)
(3) Nitric oxide
- enhances further transmission of pain signal
What factor limits non-opioids?
Ceiling effect
Dose above which there is no further pharmacological action
What is the mechanism of action of opiates?
Increase descending inhibitory pathways
Decrease neuropeptide release