Pain Assessment and Treatment

Question 1

what pain meds inhibit perception?

Answer 1

inhibit perception
1. anesthetics
2. opioids
3. alpha 2 agonists
4. benzos
5. phenothiazines

inhibit transmission
1. local anesthetics
2. alpha 2 agonists
3. NMDA agonists

modulation of spinal pathway/inhibit central sensitization:
1. local anesthetics
2. opioids
3. alpha 2 agonists
4. tricyclic antidepressants
5. cholinesterase inhibitors
6. NMDA agonists
7. NSAIDs
8. anticonvulsants

inhibit transduction/inhibit peripheral sensitization
1. local anesthetics
2. opioids
3. NSAIDs
4. corticosteroids

Question 2

describe opioids

Answer 2

1. opioid receptors throughout body
2. central and peripheral action
3. peripherally prevent neurotransmitter release and nociceptor sensitization, esp if inflam present
4. centrally, modulate afferent input onto substantia gelatinosa; blunt pain perception in cortical areas
5. best used multimodally
6. profound analgesia
7. many adverse effects

Question 3

describe the effects and uses of opioids

Answer 3

effects:
-analgesia
-sedation
-hypoventilation
-bradycardia
-vomiting
-cough suppression
-occasional dysphoria

2. very good agents for use in young, old, debilitated, ill animals
3. can be injectable, PO, transdermal patches
4. controlled drugs
5. antagonists available

Question 4

describe tramadol

Answer 4

1. synthetic opioid; atypical mu-agonist (adjuvant drug, not used in opioid category)
2. MOA:
   -moderate mu agonist (5-10 times less than morphine), weak kappa agonist
   -decrease reuptake of norepinephrine and serotonin
3. active metabolites: O-desmethyltramadol (active version)
   -very small amounts in dogs and horses = no work super well
4. no respiratory depression, no tolerance

Question 5

describe alpha 2 agonists

Answer 5

1. in locus ceruleus, thalamus, cortex
   -sedation and supraspinal analgesia
2. binding receptors in dorsal horn of the spinal cord = spinal analgesia
3. prolong the duration of nerve blocks via inhibition of C-fibers
4. effects:
   -sedation, analgesia, muscle relaxation
   -bradycardia (AV blocks), peripheral vasoconstriction (hypertension followed by hypotension), decreased CO
   -vomit, decreased GI motility
   -hyperglycemia
   -increased diuresis

Question 6

describe NMDA agonists

Answer 6

1. analgesic effect via 2 mechanisms
   -blockade of dorsal horn NMDA receptors to prevent central sensitization
   -activation of opioid receptors
2. also has a local anesthetic effect, blocking action potentials along nociceptive axons
3. generally administered as a bolus at induction of anesthesia
   -can be given as a CRI at sub-anesthetic doses
4. also include: amantadine, gabapentin, methadone, nitrous oxide

Question 7

describe NSAIDs

Answer 7

1. act peripherally at sites of inflammation
   -block formation of prostaglandins and thromboxanes
2. in spinal cord: block glutamate and substance P receptors
3. side effects: gastro-enteric system, kidneys, platelets

Question 8

describe NSAID MOA

Answer 8

1. inhibit COX-1 and COX-2
2. classified based on COX1 versus COX2 selectivity
3. COX2 selective drugs have more anti-inflammatory effects
   -meloxicam, carprofen, the coxibs
   -may have less severe adverse effects
4. COX1 selective drugs have more anti-thrombotic effects: aspirin, ketoprofen

Question 9

describe corticosteroids

Answer 9

1. act peripherally at sites of inflammation

2, block phospholipase A2 and formation of prostaglandins, thromboxanes, and leukotrienes

3. side effects:
   -GI, kidneys, coagulation, hyperglycemia, Cushing’s, immunosuppression
   -not usually used to treat pain, used more to treat acute inflammation that will cause pain
   -NO COMBINE WITH NSAIDS = more side effects

Question 10

describe local anesthetics

Answer 10

1. block the transduction and transmission of nociception by blocking Na+ channels
2. nociceptive impulse never reaches dorsal horn = spinal anesthesia
3. can be used for local techniques
   -ring block, brachial plexus block, epidural
4. IV lidocaine:
   -IV bolus and/or CRI
   –NO bupivicaine (cardiotoxic)
   –no lidocaine in cats (severe cardiovascular depression)
   -transdermal patch
5. systemic administration: analgesic, anti-inflam, anti-arrhythmic, prokinetic, free-radical scavenger, reduced anesthetic requirements
6. side effects: convulsion, coma, CV depression, cardio-resp arrest, neurotox, methemoglobinemia

Question 11

what are adjuvants? (3)

Answer 11

1. anticonvulsants
2. NMDA-agonists
3. tricyclic antidepressants

Question 12

describe gabapentin

Answer 12

1. MOA not well known but considered an anticonvulsant
   -increases synth and decreases reuptake of GABA
   -decreases synth of glutamate
   -Ca2+ channel block at spinal and supraspinal levels blocking central sensitization
   -may inhibit NMDA receptors
2. side effects: drowsiness, GI (V/D, constipation)
3. used most commonly for neuropathic pain
   -no evidence that it works on acute pain, may be helpful for chronic
4. clinical use:
   -may be useful as an adjunct to a multimodal analgesic approach
   -may decrease incidence of chronic pain if used post-op
   -behavior modification in cats

Question 13

describe amantadine

Answer 13

1. NMDA receptor antagonist, may decrease central sensitization
2. may enhance the effects of NSAIDs, gabapentin, and opioids
3. clinical use:
   -may be useful as an adjunct to a multimodal analgesic approach

Question 14

describe tricyclic antidepressants

Answer 14

1. amitriptyline
2. MOA:
   -decrease reuptake of norepi and serotonin
   -Na+ channel blockade
   -NMDA receptor antagonist
3. clinical use:
   -may be useful as an adjunct to a multimodal analgesic approach, may be useful for neuropathic pain
4. side effects:
   -low therapeutic index
   -sedation
   -anticholinergic effects: tachycardia, urinary retention, decreased GI motility
   -bradycardia