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FCP > Anaesthesia and premedication > Flashcards

Anaesthesia and premedication Flashcards

1
Q

The principle of using multiple drugs to allow minimal doses is known as

A

Balanced anaesthesia

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2
Q

Describe the sequence of anaesthetic events

A
  1. Induction
  2. Maintenance
  3. Emergence/recovery
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3
Q

Why minimise drug doses?

A

To reduce the side effects of the drug and enable balanced anaesthesia

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4
Q

What is premedication?

A

A combination of drugs or single agent given prior to anaesthesia. This is a component of most anaesthetics.

Triple/quad protocols in cats are an exception to this.

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5
Q

Why premedicate?

A
  • For balanced anaesthesia
  • To produce analgesia
  • Sedation
  • Anxiolytic/stress-reduction
  • Agent-sparing effects
  • Improved recovery
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6
Q

True/false: under GA, patients experience pain.

A

False: under GA patients don’t experience pain, but they do experience nociception.

Response to this can make patients harder to manage under the anaesthetic.

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7
Q

True/false: evidence suggests that pre-op analgesia has the same effect as analgesia given during/after the op.

A

False

Pre-op analgesia is more effective!

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8
Q

Why is pre-op analgesia more effective than just post-op?

A
  • Preventative analgesia
    • Decreases the pain after tissue injury
    • Prevent pathological modulation of the CNS (the development of hyperalgesia)
    • Prevents the development of a chronic pain state, which in turn:
      • Leads to increased cortisol, pro-inflammatory cytokines and slower wound healing
      • Increases the likelihood of the patient interfering with the wound
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9
Q

What is this graph showing us?

A

That noxious stimuli can sensitise the nervous system response to subsequent stimuli.

Therefore, pre-op analgesia is a good thing!

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10
Q

What does this figure show us?

A

The interventions that can modulate the activity in the pain pathway at different points.

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11
Q

Mode of action: opioids

A
  • Affect 4 main types of receptor in the CNS and peripherally:
    • Mu
    • Kappa
    • Delta
    • Nociceptin
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12
Q

What can antagonise opioids?

A

Naloxone

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13
Q

Advantages of opioids

A

✅ Provide sedation and analgesia

✅ Minimal CV depression → can be used in v sick patients

✅ Respiratory depression usually minimal; may be seen with fentanyl/high doses of methadone

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14
Q

Disadvantages of opioids

A

❌ May see apnoea if given intra-op

❌ Reduce GI motility and gastric emptying

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15
Q

Examples of opioids

A

Bold = most effective

  • Methadone
  • Fentanyl
  • Pethidine
  • Morphine
  • Buprenorphine
  • Butorphanol
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16
Q

True/false: morphine is licensed in veterinary species.

A

False: morphine is not licensed in veterinary species.

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17
Q

Features of butorphanol

A
  • Provides good sedation
  • Provides poor & short-lived analgesia
  • May be good for birds as they have a high number of kappa receptors
18
Q

Effects of alpha-2 agonists

A
  • Cause profound, dose-dependent sedation
  • Biphasic CV effects
    • Initial vasoconstriction resulting in increased BP, then reflex bradycardia and reduction in cardiac output
    • After 15-20 mins, BP and HR return to normal or just below
    • Some patients may not be able to cope with these effects❗️
19
Q

What antagonises alpha-2 agonists?

A
  • Atipamezole

This will antagonise sedative, drug-sparing and analgesic properties → consider what else you are prepared to give

20
Q

Advantages of alpha-2 agonists

A

✅ Useful in lively/aggressive animals at high doses

✅ Drug sparing: reduce amount of induction and inhalational agent required

✅ Provide good analgesia as there are alpha-2 receptors in the spinal cord. However, this is short-lived.

✅ Minimal respiratory depression

21
Q

Disadvantages of alpha-2 agonists

A

❌ Significant CV effects! Not suitable for sick patients/patients with CV disease.

❌ Increase the time taken for injectable anaesthetic to reach the CNS and brain. Inject slowly!

❌ Reduce blood flow to liver and therefore hepatic metabolism of drugs. Consider esp. in patients with liver disease.

❌ High degree of sedation: take care with brachycephalic dogs as there is a danger of URT obstruction.

❌ Can cause emesis esp. in cats

❌ Reduce endogenous insulin secretion → can cause transient hyperglycemia

❌ Cause increased urine secretion due to reduced renin and vasopressin secretion; consider in blocked cats, or the standing horse/cow who could slip.

22
Q

Examples of alpha-2 agonists

A
  • Medetomidine
  • Dexmedetomidine
  • Xylazine (has a poor affinity for alpha-2 receptors in smallies, and causes high side effects)
  • Detomidine
  • Romifidine
23
Q

Mode of action: Phenothiazines

A
  • Centrally acting, antagonises dopamine receptors.
  • Also acts on alpha-1, muscarinic and H1 receptors.
24
Q

Characteristics and effects of phenothiazines

A
  • Common premed component that might be combined with an opioid/alpha-2 agonist
  • Contributes to sedation and tranquillisation
25
Q

Advantages of phenothiazines

A

✅ Causes minimal respiratory depression

✅ Antiarrhythmic via alpha-1 antagonism in the heart and reduction in sympathetic tone

Clinical effects are still not really known.

26
Q

Disadvantages of phenothiazines

A

❌ No analgesic properties

❌ Takes 30-40 mins to take effect when given IM

❌ Lasts 6-8 hrs

❌ Profound vasodilation mediated by alpha-1 → can result in hypotension and hypothermia

❌ Might not be suitable for patients with sepsis, hypovolaemia or CV issues

❌ Some breeds are more sensitive than others: can get syncope (Boxers), susceptibility to CV effects (giant breeds). Duration of action may be prolonged in sighthounds → potentially consider lower doses

❌ Cannot be antagonised! ‼️

27
Q

Examples of phenothiazines

A

Acepromazine (ACP) is the only one licensed for veterinary use.

28
Q

Mode of action: Benzodiazepines

A
  • Centrally acting via GABAA receptor
  • Cause anxiolysis, hypnosis and sedation
29
Q

What antagonises benzodiazepines?

A

Flumazenil

  • This is via competitive inhibition and is short-lived
  • May not be stocked in practice as is expensive; uncommon to have in first opinion
30
Q

Advantages of benzodiazepines

A

✅ Minimal CV and respiratory depression → good for the compromised patient

✅ Drug sparing: reduce amount of induction and inhalational agent needed

✅ Contribute to muscle relaxation

✅ Cause amnesia in people; this might also be the case for veterinary patients

✅ Very good anticonvulsants

31
Q

Disadvantages of benzodiazepines

A

❌ Poor degree of sedation in healthy animals, especially if given IV

❌ No analgesic properties

32
Q

Examples of benzodiazepines

A
  • Diazepam
    • Licensed in dogs and cats
    • Can only be given IV as painful and poorly absorbed via IM
  • Midazolam
    • Licensed in horses, commonly used in smallies
    • Can be given IM and IV
33
Q

Examples of NMDA receptor antagonists

A
  • Ketamine
  • Methadone and pethidine (opioids) also demonstrate some NMDA receptor antagonism
34
Q

Advantages of NMDA receptor antagonists

A

✅ At high doses → dissociative anaesthesia = results in sensory blockade

✅ At lower doses, results in sedation

✅ At even lower doses, can provide analgesia

✅ Profoundly reduces dose of induce/inhalational agent required. Can serve as anaesthetic agent at high doses.

✅ Generally good CV stability

35
Q

Disadvantages of NMDA receptor antagonists

A

❌ Can be stimulatory to the CV system via noradrenaline release. This causes a transient increase in CO and BP.

  • Therefore unsuitable for some patients e.g. myocardial problems as may not be able to tolerate this.

❌ Variable dose-dependent respiratory depression. Not usually a problem at the doses we use.

❌ Short-acting: lasts 30-40 mins

❌ Very poor muscle relaxant, can lead to twitchiness

❌ Dries out corneas → must lubricate eyes

❌ Some patients who receive higher doses can become excitable and react to light/noise upon recovery

36
Q

Mode of action: anticholinergics

A
  • Parasympatholytic/vagolytic: reduce the activity of the sympathetic nervous system
  • Used to be used often, now not so much
37
Q

Advantages of anticholinergics

A

✅ Reduce bradycardia: sometimes used intra-op or in premed if this is a concern

✅ Can be used to reduce respiratory tract secretions e.g. brachycephalic undergoing respiratory tract surgery

38
Q

Disadvantages of anticholinergics

A

❌ Cause mydriasis

❌ Can reduce gut motility

39
Q

Examples of anticholinergics

A
  • Atropine
  • Glycopyrrolate
40
Q

Mode of action: alfaxalone

A
  • Neuroactive steroid
  • Usually considered induction agent (IV), but can be used as a premed via IM route in sicker patients
41
Q

Advantages of alfaxalone

A

✅ Can be used in a patient that has rebuffed their premed i.e. significant sedation has not been achieved

✅ Few adverse CV effects

May see mild vasodilation when given IV, not so much IM

42
Q

Disadvantages of alfaxalone

A

❌ Apnoea can be seen when given IV

FCP (34 decks)

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