4. Week 4 Pain and Analgesia Flashcards
Define pain
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What is multimodal analgesia?
an analgesic plan which affects as many stages in the nociceptive pathway as possible: Transduction Transmission Modulation Perception
Pre emptive analgesia
– Administering analgesics prior to noxious stimulus maximises effect, reduces sensitisation and enhances post operative analgesia
- means less drugs in the long run
What are challenges we face when assessing pain
Species specific
- prey species tend to mask pain more to avoid predation
Individual variation
Observer perception/ bias
Behavioural indicators may be more difficult when stressed/ anxious animal
How can we assess pain in dogs?
Multidimensional composite pain scales
e.g. glasgow canine pain scale
How can we assess pain in cats
multidimensional pain scales
Orbital tightening
ear position
muzzle position
How can we assess pain in Horses
prey species therefore try to mask
pain assessment tools
b. Physiological parameters considered unreliable
c. Behavioural indicators
i. Decreased weight bearing (orthopaedicpain)
ii. Pawing, flank watching, rolling (abdominal pain or ‘colic’)
iii. Restlessness, reduced appetite, reduced socialisation, low head carriage (non-specific)
d. Facial expression - Horse Grimace Scale, Equine Pain Face
How can we assess pain in cattle
COW PAIN SCALE LOCOMOTION SCORING Grimace scale i. Dull, uninterested in surroundings ii. Depressed iii. Hold head low iv. Inappetence, weight loss v. Drop in milk yield vi. Handled – react violently, immobilise, rigid posture, grunt, grind teeth, vii. Hind foot directly in front of other
Sheep pigs and goats when painful
GRIMACE SCALES
Goats much more vocal than sheep
sheep very stoic
GOATS less subtle
pigs - vocal, aggressive, unwilling to move,
Stoic but mask pain, decreased activity big sign as spend most time foraging
difference between pain and nociception
Pain requires a conscious perception by the brain, therefore we should talk about nociception when under GA
• Nociception - Relay of noxious stimulus from the periphery to the CNS
• Pain – integration and processing of nociceptive input by the brain allowing it to be recognised as pain (implies recognition at the cortical level consciousness)
What are 3 aspects of pain
- Sensory-discriminative - I have a sudden onset, sharp stabbing intense pain in the toes on my right foot’
- Motivational-affective -this is extremely painful, I need to go and sit down as I feel sick and might faint’
- Cognitive-evaluative - this horse has just stamped on my foot, my toes are probably broken, my foot will be in plaster for 6 weeks, I’m going to miss my skiing holiday
What is acute pain?
– Associated with injury/surgery/disease – Typically short duration persisting only as long as original insult – Relatively easy to treat - types of acute pain: Somatic Visceral Neuropathic (can also be chronic)
What is somatic pain?
Type of acute pain
• Results from chemical (inflammatory), thermal and mechanical stimuli to skin, muscle, bones
• Pain Localised to site of injury, tends to be sharp/stabbing
• A delta fibres, fast fibre transmission
What is visceral pain?
Type of acute pain
• Results from distension, ischaemia and inflammation of viscera
• Poorly localised and diffuse, can be associated with autonomic effects, or referred, burning/ dull sensation
• C fibres, slower transmission
• Autonomic components – sweating, vomiting, tachycardia
What is neuropathic pain?
- Spans acute and chronic pain. Can become chronic
- 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 chronic pain?
– Persists beyond expected time frame (>3-6 months)
– May be associated with disease/injury that is not resolving
– Maladaptive response with no useful function
– Often poorly responsive to treatment
What are 3 types of altered pain states
- Hyperalgesia
a. Exaggerated pain sensation in response to noxious stimulus - Allodynia
a. Perception of pain sensation in response to a normally non-noxious stimulus - Spontaneous/ idiopathic/ functional pain
a. Pain that arises in absence of detectable tissue or nerve injury e.g. fibromyalgia in humans
b. Difficult to identify/ prove in animals
c. Possible component of neuropathic pain e.g. phantom limb pain post amputation
What is sensitisation?
Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. The process by which a synapse becomes more efficient in its response to a stimulus
The functional and/or anatomical adaptation of CNS in response to environmental and physiological processes. Can occur by peripheral and/ or central mechanisms
What is peripheral sensitisation?
- Increased responsiveness of nociceptors (result of reduced activation threshold)
- Previously ‘Silent’ nociceptors activated
- Occurs with tissue damage and inflammation
- Altered expression of ion channels in nociceptive neurons
- Causes primary hyperalgesia and allodynia at injury site
What is central sensitisation?
- Increased efficiency of nociceptive signal transmission that may persist after cessation of nociceptive input
- Changes in membrane excitability and upregulation of post-synaptic receptors (especially NMDA receptors (important!!))
- Results from intense, prolonged and/or repeated nociceptive input
- Causes secondary hyperalgesia outside/adjacent to area of injury
- May result in development chronic pain
Pharmacological management of acute pain
NOPLAN NSAIDS Opioids Paracetamol Local anesthetics Alpha 2 agonists NMDA antagonists
