Module 6a: physiology and overview of pain Flashcards
What is pain?
unpleasant sensory and emotional experience associated with actual or potential tissue damage or secribed in terms of such damage
How do you classify pain?
Duration: acute/chronic
Site of injury: nociceptive/neuropathic/nociplastic
Describe acute pain?
recent onset
<6 weeks
associated with trauma, surgery or acute illness
limited to area damage
resolves with healing
Describe chronic pain?
no longer associated with normal tissue healing processes
Persists beyond usual course of acute illness/injury/beyond normal tissue healing
What is nociceptive pain?
Pain from actual/threatened damage to non-neural tissue-> activation of NOCICEPTORS
What is neuropathic pain?
lesion/disease of somatosensory nervous system
What is nociplastic pain?
pain that arises from NOCICEPTION despite no clear evidence of actual/threatened tissue damage
What is nociception?
neural process of encoding noxious stimuli
How does somatic and visceral nociceptive pain differ in quality and localization
Somatic:
- quality: sharp, dull, aching, throbbing
- Localization: localized
Visceral:
- Quality: gnawing, squeezing, cramping
- Localization: diffuse, poorly localized, reffered pain
How does nociceptive pain differ from neuropathic pain interms of quality, localization and associated symptoms?
Neuropathic:
- Quality: burning, electric shocks, allodynia
Localization: dermatomal/diffuse
Associated symptoms: tingling, pins and needles, numbness, itching
How does hyperalgesia differ from allodynia?
hyperalgesia: Increased pain from a stimulus that normally provokes pain
allodynia: Pain due to a stimulus that
does not normally provoke
pain.
Describe the pain pathways from injury to somatosensory cortex?
Injury activates 2 things:
- Nociceptors carries impulse via primary order neurons( A beta=fast, sharp pain, C=slow, dull) to dorsal horn
- Arives at dorsal horn, carries impulse via second order neurons in spinothalamic tract to thalamus
- Third order neurons project to somatosensory cortex from thalamus and to the peri-aqueductal grey matter (PAG) from thalamus
What is the function of the peri-aqueductal grey matter
inhibits/facilitates second order neurons
What is the inflammatory soup and what does it do
Histamine
* K
* Bradykinin
* Serotonin
* Prostaglandins
sensitizes nociceptors
Give 3 ways in which a physician manages chronic pain
Gabapentinoids:
Gabapentin &
Pregabalin
Low dose TCA:
Amitriptyline
SNRIs:
Venlafaxine &
Duloxetine
What are the three stages of the analgesic ladder
- simple analgesia: paracaetamol, aspirin, nsaids
- weak opiods: tramadol, codeine, dihyrdocodeine
- strong opiods: morphine, oxycodone, diamorphine, fentanyl
How do you manage acute pain?
Simple analgesia: Local anaesthetics:
Paracetamol Bupivacaine
NSAIDS & COX 2 inhibitors: Lignocaine
Diclofenac
Hypnotic agents:
Ibuprofen Nitrous oxide
Parecoxib Ketamine
Opioids:
Codeine
Tramadol
Morphine
Fentanyl
Alfentanyl
Alpha-agonists:
Clonidine
Dexmedetomidine
Miscellaneous:
Steroids
MgSO4
How does NSAIDS work
nsaids inhibit COX 1 and 2 which prevents the conversion of arachdonic acid into prostaglandins, prostacyclins and thromboxane
What does cox1 and cox 2 do
Cox2: tissue damage and pain
Cox1: physiological functions
What are the side effects of nsaids
Gastric irritation
* Renal dysfunction
* Platelet dysfunction
* Bronchospasm
* Hepatotoxicity
* Myocardial infarction
How do you classify opiods
Weak opioids: codeine, tramadol
Strong opioids:
- Long acting: morphine
- Short acting: fentanyl, remifentanil, sufentanyl & alfentanyl
Opiods side effects?
Nausea and vomiting
* Constipation
* Urinary retention
* Itchiness/ pruritis
* Respiratory depression
* Sedation
* Histamine release (morphine)
* Bradycardia
* Muscle rigidity
What is nalaxone and give side effects
Opioids antagonist
* 1-4mcg/kg IV
Side effects include:
* Arrythmias
* Pulmonary oedema
* Hypertension
* Anti-analgesic
What is ketamine and give its effects
NMDA receptor antagonist
* Tachycardia/ hypertension
* Bronchodilation
* Salivation
* Emergence phenomenon
