Pain physiology and analgesia Flashcards
(50 cards)
Define pain
‘Pain is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage’
Define nociception
Relay of noxious stimulus from the periphery to the central nervous system
What are the 3 types of acute pain?
Somatic
Visceral
Neuropathic
Describe somatic acute pain
- Chemical, thermal or mechanical stimuli to skin, muscles, bones etc
- Usually localised to injury site
- ‘Sharp, stabbing’ sensation – fast pain transmission
Define visceral acute pain
- Inflammation, ischaemia or distension of viscera
- Poorly localised, diffuse
- ‘Burning, dull’ sensation – slower transmitted C fibres
- Possible autonomic components e.g. vomiting, sweating, tachycardia
Define neuropathic acute pain?
- Primary lesion or dysfunction within nervous system
- May be localised or diffuse (depending on degree of nerve injury)
- ‘Burning, tingling’ sensation, may be intermittent
- Can become a component of chronic pain
What is hyperalgesia?
Exaggerated pain sensation in response to noxious stimulus
What is allodynia?
Perception of pain sensation in response to a normally non-noxious stimulus
What is spontaneous/idiopathic/functional pain?
Pain that arises in absence of detectable tissue or nerve injury
Which type of sensitisation may result in chronic pain?
Central
What is peripheral sensitisation?
- Increased responsiveness of nociceptors (result off a decreased activation threshold)
- Occurs with tissue damage and inflammation
- Causes primary hyperalgesia and allodynia at injury site
What is central sensitisation?
- Changes in membrane excitability and upregulation of post-synaptic receptors (especially NMDA receptors)
- Results from intense, prolonged and/or repeated nociceptive input
- Causes secondary hyperalgesia outside/adjacent
Why does acute pain rapidly alter an animals behaviour?
- to minimise damage
- optimise conditions for tissue healing
- stops when healing is complete
What type of pain is relatively easy to treat?
Acute pain
What type of pain is associated with tissue damage (or threat of this) due to surgery, injury or disease?
Acute pain
What is meant by chronic pain being maladaptive?
No useful function
Over what length of time does chronic pain persist?
Beyond the expected time of tissue healing
What are some consequences of poor acute pain management?
- unstable general anaesthesia
- poor animal welfare
- delayed recovery
- development of central sensitisation and chronic pain
What are the 4 stages of nociception?
- Transduction
- Transmission
- Modulation
- Perception
What is pre-emptive analgesia?
Administration of analgesics prior to noxious stimulus to maximise their effect, reduce sensitisation and enhance post operative analgesia
What is multimodal (balanced) analgesia?
Formulation of an analgesic plan that targets as many stages in the nociceptive pathway as possible
Where in the body does transduction, modulation and perception occur?
Transduction = nerve terminal Modulation = Dorsal horn of the spinal cord Perception = brainstem and cerebrum
What are the pharmacological options for management of acute pain?
N = NSAIDs O = opioids P = paracetamol (not in cats) L = local anaesthetics A = alpha-2 agonists N = NMDA antagonists
Which drug group are COX inhibitors?
NSAIDS
