Pharmacology of Pain Transmission & Modulation Flashcards
What can happen IF PAIN GOES UNTREATED?
ACUTE PAIN (a symptom of the disease - protective) can become CHRONIC PAIN (the DISEASE itself)
What are the consequences of pain affecting sympathetic stimulation?
- tachycardia, tachypnoea
- peripheral vasoconstriction
- increased myocardial work
- increased myocardial oxygen consumption
- decreased blood flow (oxygen delivery) to abdominal organs
What are the consequences of pain having neuroendocrine effects?
- adrenocorticotropic hormone release
- increased cortisol
- increased norepinephrine
- increased epinephrine
- decreased insulin
What are the consequences of pain having an effect on stress?
- decreased appetite
- insomnia
- immunosuppression (delayed healing)
- decreased quality of life
What are the categories of pain patients you will encounter?
- healthy, non-painful, in for a routine elective procedure
- healthy, underlying orthopedic issue requiring surgery
- chronic condition resulting in mild discomfort
- undergone some form of trauma in the recent past, will require surgical correction within the near future
The common thread amongst all categories of patients is that at some point they will require…
ANESTHESIA and SURGERY
What is the triad of anesthesia?
- analgesia
- muscle relaxation
- LOSS OF CONSCIOUSNESS
How does our patient being anesthetized affect the PAIN RESPONSE to injury?
- not necessarily perceiving the stimulus as “pain”
- pain pathways are still firing (nociception vs pain)
What besides chronic pain can happen IF PAIN GOES UNTREATED?
- peripheral sensitization
- central sensitization
- hyperalgesia (primary and secondary)
- allodynia
- wind-up pain
What are 2 techniques to treat and reduce pain?
- pre-emptive analgesia: 1st key strategy when pain is anticipated; providing analgesia BEFORE the insult can significantly reduce both intra- & post-operative analgesia
- multimodal analgesia: combined analgesics from two or more drug classes or analgesic techniques that employ different mechanisms of action, targeting different (peripheral or central) pain pathways, thus achieving a synergistic effect at lower analgesic doses
What does pre-emptive analgesia prevent?
- sensitization
What types of procedures or conditions are considered mildly painful?
castration (certain spp/individuals), minor dental procedures, minor laceration repairs, small cutaneous or subcutaneous mass removals, cystitis, mild otitis, chest drains
What types of procedures or conditions are considered moderately painful?
castration (certain spp/individuals), ovariohysterectomy, extracapsular cruciate repair, uncomplicated simple laparotomy, urethral obstruction, early or resolving pancreatitis, localized burn
What types of procedures or conditions are considered severely painful?
complicated/invasive laparotomy, fracture repair, intra-articular surgical procedures, limb amputation, total ear canal ablation, necrotizing pancreatitis, localized/extensive burn
What does a balanced (multimodal) analgesia do?
Inhibits transduction, inhibits transmission, modulates the spinal pathway, AND inhibits perception
What are local anesthetics?
- inhibit sodium channels
- provide complete pain relief at the effected nerve site
Where do local anesthetics work?
- inhibit transduction (inhibit the peripheral sensitization of nociceptors)
- inhibit transmission (inhibit impulse conduction)
- modulate the spinal pathway (inhibit central sensitization)
What are opioids?
- decrease pain perception, anxiety, & distress
- most effective when given before pain onset
- rapid onset & long duration (rapid onset w/ IV administration; longer duration w/ IM administration)
Where do opioids act?
- inhibit transduction (inhibit peripheral sensitization of nociceptors)
- modulate the spinal pathway (inhibit central sensitization)
- inhibit perception
What are alpha2 agonists?
- provide sedation, analgesia, & anxiolysis
- examples: Dexmedetomidine (Domitor), Xylazine (Rompun)
Where do alpha2 agonists act?
- inhibit transmission (inhibit impulse conduction)
- modulate the spinal pathway (inhibit central sensitization)
- inhibit perception
What are N-methyl-D-aspartate (NMDA) antagonists?
- have analgesic properties - primarily important in addressing ‘wind-up’ pain
- NMDA receptors are important in the development of central sensitization
- at low dose can improve opioid efficacy (decreases postoperative opioid requirements)
- has excitatory effects in the CNS
- stimulatory effects on the cardiovascular system
What are NSAIDs?
- analgesic
- antipyretic
- anti-inflammatory
- prevents sensitization
Where do NMDA antagonists act?
- modulate the spinal pathway (inhibit central sensitization)
where do NSAIDs act?
- inhibit transduction (inhibit peripheral sensitization)
- modulate the spinal pathway (inhibit central sensitization)
How do we treat mild postoperative pain?
non-opioid analgesic = NSAIDs + local anesthetic infiltration
How do we treat moderate postoperative pain?
NSAIDs + local anesthetic infiltration + intermittent doses of OPIOIDs
How do we treat severe postoperative pain?
- NSAIDs + local anesthetic peripheral neural blockade (w/ or w/o catheter) + use of sustained release OPIOIDs =/- NMDA antagonist (KETAMINE) +/- ancillary pain management techniques
Which drugs inhibit transduction?
- local anesthetics
- opioids
- NSAIDs
- corticosteroids
Which drugs inhibit transmission?
- local anesthetics
- alpha2 agonists
Which drugs modulate the spinal pathway?
- local anesthetics
- opioids
- alpha2 agonists
- NMDA antagonists
- NSAIDs
Which drugs inhibit perception?
- anesthetics
- opioids
- alpha2 agonists
- benzodiazepines
What are 2 types of ancillary pain management techniques?
- manipulative therapies
- alternative techniques
What are manipulative therapies?
- temperature - application of heat (improve circulation) or cold (decrease inflammation)
- massage
what are alternative techniques?
- acupuncture
- laser therapy
Which drug is most effective for treating chronic “wind-up” pain?
ketamine
Which drug gives complete pain control at the site?
lidocaine