Pain and Analgesia Flashcards
Define pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
What is pain?
Individual experience
Multidimensional
Protective function
What are the different types of pain?
Physiologic
Nociceptive/Inflammatory
Neuropathic
What are the characteristics of physiologic pain?
Short duration, preprogrammed responses, no tissue damage
What are the characteristics of nociceptive/inflammatory pain?
Tissue damage, allodynia, hyperalgesia etc
Pathologic forms
What are the characteristics of neuropathic pain?
Damage or dysfunction of peripheral nerves or CNS
Define acute pain
Obvious cause
Relatively short duration
Resolves with healing
Protective function
Define chronic pain
Multiple causes
Persist after healing
No adaptive function
Often refractory to treatment
What is the process of nociception?
Transduction Transmission Modulation Projection Perception
What is the process of transduction of pain?
Peripheral nerves are extensions of CNS and free nerve endings transduce noxious stimuli into electrical signals and action potentials
Varied sensitivity to mechanical, thermal and chemical stimuli
What is peripheral sensitisation?
IMAGE
What is the process of transmission of pain?
First order neurons synapse in dorsal horn
Myelinated A-delta fibres = first pain
Unmyelinated C fibres = second pain, visceral pain
What is the process of modulation of pain?
Peripheral sensory nerve impulses are amplified or suppressed in the spinal cord
Dorsal horn has inter-neurons and ascending neurons
What is the gate theory of control?
IMAGE
What is the process of inhibitory neurotransmission in the dorsal horn?
IMAGE
What is the process of central sensitisation?
IMAGE
What are the ascending pathways for nociception? (process of projection)
IMAGE
What is the process of perception of pain?
Unpleasant sensation in the CNS resulting in a behavioural response to pain which varies according to species
What are the descending pathways of pain?
Originates in the brian (amygdala, hypothalamus)
Relayed via the brain stem, rostral ventral medulla
Spinal cord - release of inhibitory neurotransmitters (serotonin, norepinephrine, endogenous opioids)
Takes part in modulation
What are the consequences of pain?
IMAGE
Why is peripheral and central sensitisation important?
The level of pain perceived is more severe
Analgesic drugs may be less effective if given once pain is present
One type of analgesic may not be effective on its own
How is pain assessed in practice?
Visual analogue scale Numerical rating score Simple descriptive scale Composite scoring system Multidimensional scoring system
What are the methods of pain scoring in equines?
Composite orthopedic pain scale
Equine acute abdominal pain scale
Complex numerical rating scale - postop colic
Post abdominal surgery pain assessment scale
What drug groups can be used for pain management?
NSAIDs Opioids Ketamine Alpha-2-agonists Local anaesthetics
What is pre-emptive analgesia?
The prevention or minimisation of pain by the administration of analgesics before the production of pain or the introduction of noxious stimulus if pain already exists
What is multi-modal analgesia?
The administration of multiple drugs that act by different mechanisms of action to produce the desired analgesic effect
What are the advantages of multi-modal analgesia?
Additive or synergistic effects
Reduced side effects
Reduced dose
What drugs can be used for systemic analgesia?
Opioids NSAIDs Ketamine Lidocaine MLK Alpha 2 agonists Tramadol Gabapentin/Pregabalin
What agents can be used for local analgesia?
Local anaesthetics
Opioids
Alpha 2 agonists
Define opium
Mixture of alkaloids from the poppy plant
Define opioid
Any natural occurring, semi-synthetic or synthetic compound that binds to opioid receptors and shares the properties of the natural occurring endogenous opioids
Define opiate
Any natural occurring opioid, derived from opium
Define narcotic
Used to denote an opioid but also to describe non-opioid drugs of addiction
What are the effects mediated by DOP opioid receptors?
Spinal and supraspinal analgesia, reduced gastric motility
What are the effects of KOP opioid receptors?
Spinal analgesia, diuresis, dysphoria
What are the effects caused by MOP opioid receptors?
Analgesia, sedation, bradycardia, respiratory depression, inhibition of GI tract, opioid tolerance and hyperalgesia endocrine effects and immunological effects
What are the effects of NOP opioid receptors?
Spinal analgesia, hyperalgesia and allodynia as well as supraspinal inhibition of opioid tone
What are some MOP selective agonists?
Morphine Pethidine Methadone Fentanyl Buprenorphine - partial
What are some KOP selective agonists?
Butorphanol
Nalbuphine
What are the location of MOP receptors?
Throughout pain pathways of CNS Spinal cord dorsal horn CTZ Basal ganglia Limbic centres Cortex and thalamus Myenterix plexus
Where are KOP receptors located?
Spinal cord dorsal horn Basal ganglia Limbic centres Cortex and thalamus Myenteric plexus
Where are the DOP receptors located?
Spinal cord dorsal horn
Basal ganglia
Cortex and thalamus
What are the selective actions of MOP receptors?
Analgesia (strong) Cough suppression Constipation Sedation Motor excitation in some species Respiratory depression Tolerance and dependence Vomiting
What are the selective actions of KOP receptors?
Analgesia (moderate)
Sedation
Dysphoria
What are the selective actions of DOP receptors?
Analgesia (mild)
Motor excitation?
What is a mixed opioid agonist-antagonist?
Butorphanol
Antagonist of MOP receptors so relatively poor analgesia
Agonist at some KOP receptors giving some analgesia, sedation and dysphoria
What are opioid antagonists?
Naloxone
Diprenorphine
What is a partial agonist?
Buprenorphine
Has the same overall action as agonists but doesn’t produce maximal effect giving analgesia but not as profound as full agonists
What are the possible routes of administration of opioids?
IV, IM, SC, oral, oral transmucosal, spinal/epidural, intra-articular, transdermal
What are the side effects of opioids?
Arousal
Dysphoria
Vomiting and nausea
Variation in pupillary diameter (miosis dogs, mydriasis cats)
Thermoregulaion (decrease in dogs, increase in others)
Respiratory depression
Bradycardia
What regulations cover use of pure opioid agonists?
Must be kept in a locked cupboard
Records kept of purchase and use
Special prescription requirements
Must be disposed of according to legislation
What regulations cover use of partial opioid agonists?
Should be kept in a locked cupboard with pure opioids but no record of use is necessary
What is tramadol?
Weak MOP agonist
Serotonin re-uptake inhibiting
Norepinephine re-uptake inhibiting
NMDA receptor antagonist
What are the actions of NSAIDs?
Anti-inflammatory
Analgesic
Anti-pyretic
Acute and chronic use
What are the indications for ketamine?
Skin surgeries and neuropathic pain
How is ketamine used to manage pain?
Adjuvant to pain management at sub-anaesthetic doses blocks NMDA receptor
