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CPS > Pain relief > Flashcards

Pain relief Flashcards

1
Q

Where do analgesics act?

A

» They may act at the site of injury and decrease the pain associated with an inflammatory reaction (e.g. NSAIDs)
» They may alter nerve conduction (e.g. local anaesthetics)
» They may modify transmission in the dorsal horn (e.g. opioids & some antidepressants)
» They may affect the central component and the emotional aspects of pain (e.g. opioids & antidepressants)

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2
Q

Which is better, post injury analgesia or pre-emptive?

A

pre-emptive

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3
Q

What receptor do opioids act on?

A

Opioid receptors identified; mu, delta, kappa, nociception
Stimulate the mu receptor and you get great analgesic effects
» Subtype specific drugs with fewer side effects

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4
Q

What are the most common opioids?

A

Morphine
Methadone
Fentanyl
Pethidine (Meperidine)

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5
Q

What are the side effects of opioids?

A

» Mania & respiratory depression?
» CVS effects, pruritis, urinary retention, ileus, pancreatic duct, temperature, miosis, mydraisis, vomiting & nausea

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6
Q

Is morphine a good analgesic? How long does it last?

A

» The most efficacious opioid at relieving pain
» It is a full agonist at mu, delta and kappa receptors
» Duration of action approx 4 hours

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7
Q

how can morphine be administered?

A

» PO, SC, IM, IV, CRI, epidural
» Oral bioavailability approx 25%, & with an increased dose, duration of action may extend to 8 hours with this route

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8
Q

How does methadone work? How long for?

A

» A synthetic mu agonist (full) & affinity for NMDA receptor
» Has effects as a norepinephrine and serotonin reuptake inhibitor
» Following IV - duration of action is approximately 4 hours (can be longer with sc

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9
Q

Where would you use methadone?

A

» Use as premed, for sedation, intra op (v slow IV), on recovery, and as CRI (kinetics not yet published), poor oral availability
» Licensed for dogs and cats. CD II

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10
Q

How does Pethidine (Meperidine) work?

A

» Pethidine is a short acting synthetic agonist at the mu receptor.
» Also shown to block sodium channels
» Agonist at alpha 2 B subtypes

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11
Q

What are some of the problems with Pethidine (Meperidine)?

A

» Pethidine has significant negative inotropic effects & tends to increase heart rate
» Can also induce histamine release, don’t give iv
» The combination of a monoamine oxidase inhibitor and pethidine should be avoided to prevent a serotonin syndrome occurring

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12
Q

Where would you use Pethidine (Meperidine)?

A

» Increases HR so there is no drop in CO- Can use in animals with dodgy hearts
» CD II (licensed for dogs, cats, horses (spasmodic colic)

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13
Q

How does Fentanyl work? How long does it last?

A

» Fentanyl is a highly lipid soluble short acting mu opioid agonist. CD II
– Works within 30s but only lasts for 30mins

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14
Q

When would you use fentanyl?

A

– Intraoperatively as bolus, with peak analgesic effects occurring in 3-5 minutes
– At induction with a benzodiazepine
– For compromised patients fentanyl+BZD may be sufficient for intubation
– CRIs are very effective
– Transdermal fentanyl patches

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15
Q

What are some of the problems with fentanyl?

A

» Respiration slows or may cease following a bolus

– Bradycardia can be significant

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16
Q

Alfentanil, sufentanil and remifentanil can be used during anaesthesia to blunt sympathetic stimulation, how is Remifentanyl given and why?

A

All have context sensitive half lives shorter than fentanyl
Remifentanil always given by CRI
Given as low dose (for analgesia) or higher doses as part of TIVA
MAC reduction of these opioids has been shown in dogs and cats

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17
Q

Does tramadol have analgesic effects?

A

– It basically makes dogs appear happy but without any analgesic effect

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18
Q

What are the Partial & Mixed Agonist/Antagonist opioids?

A

Buprenorphine and Butorphanol

19
Q

How does Buprenorphine work and how long for?

A

(eg vetergesic) is a partial agonist with a strong affinity for mu receptors and kappa antagonist properties
• Highly potent but not as efficacious as pure opioids
• Peak effect IV admin 45-60mins

20
Q

What is Buprenorphine used for?

A
  • Mild to moderate pain, good sedation, long duration of action, preservative in multi dose vials
  • Licensed for dogs and cats and horses
  • OTM (oral transmucosal) route works v well (cats>dogs)
21
Q

How does Butorphanol work and how long for?

A

Butorphanol is a kappa opioid agonist and mu antagonist (short-medium duration)
• The analgesic effects only last for around 10 mins but it’s a great sedative

22
Q

What is Butorphanol used for?

A
  • Available as oral form (Torbutrol)
  • Useful in combination with acepromazine for sedation e.g. cardiac patients
  • Licensed for dogs, cats & horses
  • Antitussive - prevents coughs
23
Q

What are LA’s (chemically)?

A

LAs are weak bases and largely ionised at physiological pH.

» Problem in inflamed tissue as they are very acidic

24
Q

The speed of onset of a LA is proportional to…

A

Their speed of onset is inversely related to their degree of ionization.
» ?Longer to start working in inflamed tissue

25
Q

The duration of activity of a LA is proportional to…

A

Their duration of effect is directly related to their degree of protein-binding.
Their potency is related to their lipid solubility. Their unionized form is their active form

26
Q

Name some common LA’s?

A
  • Lidocaine
  • Prilocaine (+lidocaine)
  • Bupivicaine
  • Mepivicaine
  • Ropivicaine
  • Etidocaine
  • Amethocaine
  • Proparacaine
  • Cocaine
27
Q

The toxic dose of a LA is very close to ……

A
  • The toxic dose of local anaesthetics is very close to the therapeutic dose
  • Always aspirate before injecting local anaesthetic as toxicity usually results from accidental intravascular injection
28
Q

What are the toxic reactions to LA’s like?

A

Toxic reactions to local anaesthetics include CNS toxicity, cardiovascular toxicity and methaemoglobinaemia – if it looks twitchy AF then stop; it’s not good

29
Q

How do we administer intradermal anaesthetic?

A
  • Lidocaine is most often used (0.5-2.0%)
  • Anaesthesia is produced by multiple intradermal (or subcut) injections of 0.3-0.5ml (dogs) and a 22-25g needle
  • The local is slowly injected as needle is advanced along the proposed surgical site
30
Q

What forms of topical lidocaine are there?

A 
‘Intubeaze’ (2%,) – one spray delivers 2-4mg of lidocaine. Used for intubating cats (& other spp) and can be used to desensitize small area of mucosa. 
Lidocaine jelly (2% 20mg/ml) for catheterising the urethra
Lidocaine & prilocaine cream (EMLA) useful for IV catheter placement (cat induction video)
Proparacaine 0.5% and butacaine 2% can be used to anaesthetize the cornea for 10-20minutes
Local anaesthetics such as bupivicaine or lidocaine can also be placed into the abdomen or thoracic cavity (e.g. down a chest drain) or to block nerves directly
31
Q

How can LA be administered intrarticularly?

A

After arthroscopy, cruciate ligament repair and arthrotomy for removal of cartilage debris
• Disadvantages: Minimal analgesia for surrounding tissues
• Some systemic analgesia is still required

32
Q

What are soaker catheters?

A
  • Useful for analgesia for total ear canal ablations (TECA), limb amputations & extensive reconstructive surgery
  • Relatively large bore (6 - 12 French) catheters with very tiny holes
  • Allow distribution of local anesthetic into the surgical site
  • Placed just before closing incision and secured to the skin at the end of the surgery
33
Q

Where do you place the epidural?

A

Behind L7 and infront of S1 in the venous sinus

34
Q

How do NSAIDS work?

A

• Inhibit prostaglandins (COX, LOX)

35
Q

What NSAIDs are licensed for horses?

A
  • Phenylbutazone
  • Suxibuzone
  • Firocoxib
  • Meloxicam
  • Flunixin meglumine
  • Vedaprofen
  • Carprofen
36
Q

What other formulations of NSAID are there?

A
  • Ophthalmic preps
  • Piroxicam (Urinary tract) 0.3 mg/kg
  • Topical ointment
  • Locally (ketoprofen)
37
Q

Pardale V for dogs (paracetamol & codeine), can paracetamol be used in cats? Pigs?

A

NEVER USE PARACETAMOL IN CATS

Paracetamol used in pigs for pyrexia from resp dz. Used as a premix with feed

38
Q

NSAIDs are contraindicated in patients with:

A
  • Renal or hepatic insufficiency
  • Hypovolaemia
  • Congestive heart failure & pulmonary disease
  • Coagulopathies, active haemorrhage
  • Spinal injuries
  • Gastric ulceration
  • Concurrent use of steroids
  • Shock, trauma (esp head trauma)
  • Pregnancy
39
Q

What are the effects of A2 agonists?

A
  • Sedation (A)
  • Decrease MAC
  • Analgesia (somatic & visceral) (A & B)
  • Hyper (B) then hypotension (A)
  • Decreased CO & HR, increased SVR
  • Respiratory depression
  • Increased urine productio
  • Decreased GI motility
  • Decreased surgical stress response
  • Hyperglycaemia, GH enhanced,
  • Thermoregulation affected
  • Sweating
40
Q

What are the subtypes of A2 receptors?

A 
3 subtypes (4) A,B,C
–	Diverse sites: CNS & PNS
41
Q

What are the uses of A2 agonists?

A 
–	Premedication
–	PIVA/TIVA
–	Epidural
–	Rescue analgesia
–	One of the few classes of drugs with an antagonist- atipamazole
42
Q

What are the premed combinations?

A
  • Acepromazine + opioid
  • Alpha 2 agonist + opioid or BZD or ketamine
  • BZD + Ket
  • Opioid + BZD
  • Alpha 2 + BZD + opioid
43
Q

How long should we provide analgesia for?

A

– 24-72 hours for routine ops

44
Q

What options do we have available for post op analgesia?

A

– NSAIDs (daily, oed, monthly)
– Opioids (patch, long acting formulations, oral forms (tramadol, morphine, OTM buprenorphine)
– LA blocks

CPS (16 decks)

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