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CPS > Analgesics notes > Flashcards

Analgesics notes Flashcards

1
Q

How do opioids work?

A
  • Modify transmission in dorsal horn
  • Affects central/ emotional components of pain
  • Natural (opiates) and synthetic
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2
Q

Discuss the receptors opioids act on

A
  • Most domestic species have mu receptors
  • Birds have kappa receptors
  • Also act on delta and nociceptors
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3
Q

Describe the use of morphine

A
  • Full mu/ delta/ kappa antagonist
  • Po/ SC/CRI/IM/IV/Epidural
  • Oral increases time of action
  • Reduces MAC/ MIR
  • Schedule 2 CD
  • No license
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4
Q

Discuss the use of methadone

A
  • Full mu agonist
  • Affinity for ndma receptor
  • Norepinephrine/ serotonin reuptake inhibitor
  • IV
  • 4hrs
  • Premed for sedation
  • CD schedule 2
  • Dogs/ cats
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5
Q

Describe use of pethidine

A
  • Short acting 1.5hrs
  • Mu agonist/ some A2b
  • Blocks Na channels
  • Negative inotrope (incr HR)
  • Histamine release so NOT IV
  • Dogs/ cats/ horses
  • Schedule 2
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6
Q

Discuss the use of fentanyl

A
  • Short acting- 20 mins
  • Mu agonist
  • Lipid soluble
  • Intra op bolus
  • Induction with BZD to heelp with intubation
  • CRI/ transdermal patches good for continuous release BUT ingestion risk for animal/ children
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7
Q

Describe tramadol

A
  • Licensed in dogs
  • Low potency partial mu agonist
  • 5ht uptake inhibitor: may cause sedation instead of pain relief
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8
Q

Describe buprenorphine

A
  • Partial agonist mu (mild kappa antagonism)
  • Potent but not like pure opioids
  • Sedation/ mild-mod pain
  • Oral trans mucosal route
  • Easily displaced
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9
Q

Describe butorphanol

A
  • Kappa agonist/ mu antagonist
  • Short to med duration
  • Used with ACP for sedation of cardiac patients
  • License with dogs/ cats/ dogs
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10
Q

Which pain pathways can be treated with which drugs?

A
  • Peripherally: NSAIDs/ LA
  • Peripheral nerve: LA block
  • Dorsal horn: LA, Opioids, A2s
  • Brain: Opioids/ A2s
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11
Q

What is post injury hypersensitivity?

A
  • Red, inflamed areas hurt because of post injury hypersensitivity, makes pets more likely to nibble and chew wounds.
  • Can treat with NSAIDs for example which causes a temporary decrease in pain
  • Better to give analgesic before injury so hypersensitivity reaction doesn’t occur therefore much less pain.
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12
Q

List some side effects of opioids

A 
CVS effects
Vomitting
Fever
Pruritis
Ileus
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13
Q

What receptor does ketamine act upon?

A

NMDA

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14
Q

List the receptors used by the different opioids

A
  • Morphine: mu, delta, kapp (full)
  • Methadone: mu( full), NMDA (partial)
  • Pethidine: mu
  • Fentanyl: mu
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15
Q

Which opioid can you NOT give IV?

A

Pethidine (histamine response)

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16
Q

Describe the LA method of action

A
  • Unionised LA crosses cell membrane (active form). Its then ionised so it can block the Na+ channel.
  • Results in the cell not being able to depolarise emaing it cannot transmit a pain signal.
17
Q

Why is pH a problem in inflammed tissue?

A

-Inflammation causes the pH to decrease, becomes more acidic
-Results in LAs being ionised quicker so they cannot ente the cell so work less effectively.
-Will switch between ionised/ unionised so some level of efficacy just takes longer
-

18
Q

What do LA drugs end in?

A

‘caine’

19
Q

Describe LA toxicity

A

The toxic dose very close to effective dose= narrow window

  • ALWAYS aspirate before injecting to ensure not IV as this causes toxicity
  • CNS signs, CVS signs, methoaemoglobinaemia
20
Q

Other than infiltrating somatic tissue, what other ways do we use LAs?

A
  • Intubeaze (lidocaine spray)
  • EMLA (Lidocaine/ prilocaine)
  • Proparacaine (used for cornea)
  • Direct into abd/ thoracic cavities (lidocaine/ bupivicaine)
  • IV (LIDOCAINE ONLY)
21
Q

What are the effects of IV lidocaine?

A
  • Decrease MAC

- Never give IV to cats!!!

22
Q

What are the different techniques for placing a nerve block?

A
  • Nerve stimulator

- Ultrasound

23
Q

Why would you do a phrenic block?

A

For forelimb surgery

24
Q

What are soaker catheters?

A
  • Useful for total ear canal ablations

- Large bore catheters with tiny holes

25
Q

What is an IVRA and how do you perform one?

A
  • Intra Venous Regional Anaesthesia
  • Esmarch bandage applied and tourniquet proximal
  • Bandage removed and lidicaine injected into a vein distal to tourniquet
  • Tourniquet can remain for up to 90 minutes
26
Q

Describe the action of NSAIDs

A
  • Inhibit prostaglandins (COX/ LOX)

- NSAIDS inhibit cyclooxygenase (steroids inhibit phosphilipase so no arachidonic acid formed)

27
Q

What does COX 1 do?

A
  • PG synthesis along length of GIT (maintain blood flow, increase mucus production, vasodilation to the kidney)
  • Found in neurons
  • Present in fetus, amniotic/ uterine tissue
  • Found in platelets
  • ‘Housekeeping’ enzyme: keeps everything in balance
28
Q

What effects does inhibiting COX 1 have?

A
  • Prevents blood clotting as COX 1 converts arachidonic acid into TBX A2
  • TBX A2 potent vasoconstrictor & aggregatory mediator
29
Q

What effects does inhibiting COX 2 have?

A

Causes a reduction in rate of healing of gastric mucosa so in patients with IBD you make their symptoms worse

30
Q

How does Grapiprant work?

A

Instead of inhibiting COX it inhibits PGs

PGE2 and EP4

31
Q

In which patients are NSAIDs contraindicated?

A
  • Renal
  • Hypovolaemia
  • Gastric ulceration
  • Steroid patients
  • Hepatic (less of a worry, must be advanced)

(i.e. be most wary of kidneys and stomach!!)

32
Q

What are the subtypes of A2 receptors?

A

A
B
C1
C2

33
Q

What are the effects of A2 agonists?

A
  • Sedation
  • Reduce MAC
  • Analgesia
  • Hyper/ hypotension
  • Decreased CO/HR
  • Respiratory depression
  • Increase urine production
  • Decreased GI motility
34
Q

Why do you get a biphasic reaction with A2 agonists/

A
  • Vasconstriction causing BP to increase

- Baroreceptors compensate for this causing decrease

35
Q

What causes the NMDA receptor to be triggered?

A

Repeated trauma

Causes chronic sensitisation and upregulation of pain

36
Q

How long post op should we provide pain relief?

A

24-72 hrs for routine procedures

CPS (11 decks)

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