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Clinical Anesthesia > Injectable Drugs > Flashcards

Injectable Drugs Flashcards

1
Q

What is the purpose of Injectable Agents?

A

To induce Anesthesia

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2
Q

What is the definition of Anesthesia?

A
  • Without sensation, without pain
    Includes NAP:
    Narcosis
    Analgesia and autonomic reflex suppression
    Peripheral skeletal muscle relaxation/ immobilization
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3
Q

What is GABA, and where is it found?

A

Gamma-amino-butyric acid

- The main inhibitory transmitter present in the CNS

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4
Q

How many receptors does GABA have?

A

2
GABA a: receptor operated ion channel
GABA b: G-protein coupled receptor

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5
Q

All anesthetic agents seem to target and affect the _____ _______ somehow

A

GABA receptors

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6
Q

What happens when anesthetic drugs bind to the GABA receptors?

A
  • Promote GABA release
  • Assist GABA binding
  • Promote greater channel open time to hyperpolarize excitatory channels and thus rate of excitatory firing
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7
Q

What are the most commonly used anesthetic injectable agents in small animal practice?

A
  • Propofol
  • Alfaxalone (especially in pediatric patients)

+ Ketamine

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8
Q

What is the mechanism of action of Propofol?

A
  • Enhances the inhibitory effects of GABA at the GABA a receptor
    note: higher doses of Propofol will improve the activity of glycine receptors and inhibit nicotinic Ach receptors (causing an inhibitory effect of the ANS, both PNS and ANS?)
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9
Q

What is the % protein binding, pH and pKa of Propofol?

A

% Protein binding: 95%

pH: 7.8

pKa: 11

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10
Q

Where in the body is Propofol metabolized and excreted?

A

Metabolized: liver (maybe the lungs too)

Excreted: urine and bile (can cause the urine to go green-yellow)

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11
Q

What are the risks associated with using Propofol in cats?

A
  • Have longer recoveries (metabolism capabilities are reduced)
  • Can cause Heinz body anemia (due to oxidative injury)
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12
Q

Can Propofol be used in the pregnant animal?

A

Yes, although Propofol does cross the placenta it is rapidly removed from fetal circulation

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13
Q

What are the effects of Propofol on the CNS?

A
  • Hypnotic
  • Depresses CNS activity
  • NO ANALGESIA
  • Anticonvulsant: used in seizure management
  • Anti-oxidant and free-radical scavenging properties (similar to Vit E)
  • Antiemetic effects too

-Reduces intracranial pressure: thus is favoured in head trauma patients

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14
Q

What are the effects of Propofol on the CVS?

A
  • Vasodilation
  • Hypotension: by resetting the baroreceptors in the aortic arch and carotid bodies, this means the body will NOT naturally compensate for the drop in BP and thus the BP remains low (e.g. HR and SV do not increase)
  • Bradycardia

+/- Nitric oxide release leading to FURTHER vasodilation

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15
Q

What are the effects of Propofol on the Respiratory System?

A
  • Central respiratory depression: can last several mins and may need manual ventilation
  • Bronchodilation
  • Inhibition of laryngeal reflexes
  • Apnea post induction
  • Transient cyanosis at induction
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16
Q

What are the effects of Propofol on the pancreas?

A

In human medicine it has been linked to pancreatitis, while this isnt noted in vet medicine very often, it is important to avoid Propofol in a patient with pre-existing pancreatitis

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17
Q

Why might Propofol be avoided for constant rate infusion in cats?

A

Due to the risk of Heinz body anemia (due to oxidative damage of feline red cells)

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18
Q

Which stage and plane of anesthesia is considered appropriate for most surgery?

A

Stage III, and trying to keep patient between planes 2 and 3 (moderate and deep)

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19
Q

What is the mechanism of action of Alfaxalone?

A
  • It enhances the inhibitory effects of the neurotransmitter GABA at the GABA receptors
20
Q

What is the % protein binding and pH of Alfaxalone?

A

% Protein binding: 17 - 50%

pH: 6.5 - 7.0

21
Q

Where in the body is Alfaxalone metabolized and excreted?

A

Metabolized: liver

Excreted: urine and bile

22
Q

What are the effects of Alfaxalone on the CNS?

A
  • Rapid relaxation and induction
  • Reduces Cerebral Metabolic Rate and Cerebral Blood Flow: similar to Propofol, but Propofol will always be 1st choice in head trauma patients with increased intra-cranial pressures
23
Q

What are the effects of Alfaxalone on the CVS?

A

Fewer CVS effects than Propofol

  • NO hypotension in healthy patients
  • Mild tachycardia: as a response to mild vasodilation
24
Q

What are the effects of Alfaxalone on the Respiratory System?

A

Minimal: only when injected slowly and appropriately: given over a 60 sec period

BUT, significant resp depression is seen in overdoses or given too quickly

25
Q

Does Propofol and Alfaxalone provide analgesia?

A

No

26
Q

Between Propofol and Alfaxalone, which is a better induction and maintenance agent for cats?

A

Alfaxalone: not metabolized by glucoronidation, and no Heinz body anemia seen

27
Q

What is the mechanism of action of Ketamine?

A
  • Antagonist of NMDA receptors

Binds to the receptor and prevents Ca++ from entering the cell, thus excitatory function is limited

28
Q

What is the % protein binding and pH of Ketamine?

A

% Protein binding: 50%

pH: 3.5 - 5.5

note: so acidic, it will sting upon IM or SQ injection

29
Q

Where in the body is Ketamine metabolized and excreted?

A

Metabolized: liver

Excreted: urine

30
Q

Can Ketamine be used in dogs and cats with renal dysfunction?

A

Dogs with renal dysfunction: Yes, due to excretion as an inactive metabolite

Cats with renal dysfunction: No, due to excretion as an ACTIVE metabolite

31
Q

What are the effects of Ketamine on the CNS?

A
  • Dissociative anesthesia
    Superficial sleep, amnesia + Analgesia
    May appear ‘awake’ but immobile and unaware of surroundings: eyes wide open- must lube
    Palpebral, laryngeal and eye reflexes are maintained
  • Can induce seizure-like activity
  • Increases Cerebral Metabolic Rate and Cerebral Blood Flow
32
Q

What are the effects of Ketamine on the CVS?

A
  • Increase HR and BP: this can increase intracranial pressure
33
Q

Why must Ketamine never be used for induction of Moribund patients?

A
  • Causes a direct negative inotropy on the heart + vasodilation, which WILL kill your patient
34
Q

What are the effects of Ketamine on the Respiratory System?

A
  • Mild, transient decrease in ventilatory rate and tidal volume
  • Apnea
  • Increased salivation and respiratory secretions
  • Bronchodilation: good for asthmatic patients
35
Q

What is Tiletamine, and what species is it used for?

A

Tiletamine is an analogue of Ketamine: thus has similar pharmacology

Used in darts for wildlife (except Tigers!)

36
Q

What are the differences between the S(+) and R(-) enantiomers of Ketamine?

A
  • S(+) is 3-4x more potent that R(-)
  • S(+) is 2x longer in action than R(-)
  • S(+) provides more analgesia than R(-)
  • S(+) provides less dysphoria R(-)

note: in human medicine you can get pure S(+) Ketamine, however this is VERY expensive
note: in vet medicine, we use a Ketamine that has BOTH S(+) and R(-), making it more affordable

37
Q

What are the most commonly used Barbituates used in vet medicine?

A

Thiobarbiturates: thiopentone, thiamylal = short acting

Oxybarbiturates: pentobarbital, phenobarbital = long acting

38
Q

What is the mechanism of action of Thiopentone?

A
  • Binds to GABA receptor
  • Enhances inhibtory effects of GABA by increasing the binding of GABA and benzodiazepines, and allowing a longer opening time for Cl- ions and the cell becomes hyperpolarized and impulse transmission is slowed down
  • This is used as an induction agent, as it produces unconsciousness through gradual depression of the CNS
39
Q

What is the pH and pKa of Thiopentone?

A

pH: 11 - 12 (HIGHLY alkaline): must never be administered any other way except IV

pKa: 7.6

40
Q

Where in the body is Thiopentone metabolized and excreted?

A
  • Metabolized: liver

- Excreted: urine

41
Q

What are the effects of Thiopentone on the CNS, CVS, RS and Kidneys?

A

CNS:
Hypnosis
Reduced metabolic rate and oxygen consumption: thus reducing cerebral blood flow and intracranial pressure

CVS:
Vasodilation + Hypotension
Tachycardia as a compensatory mechanism
Arrythmias

RS:
Depression: Intubation is required

Kidneys:
Decreases renal blood flow

42
Q

What are the uses of Thiopentone?

A
  • Emergency management of gross movement during horse anesthesia
  • Control of convulsions
  • Neurosurgical patients: due to the profound decrease in intracranial pressure
43
Q

What is the use of Pentobarbitone?

A

Euthanasia solution

44
Q

What are the effects of Pentobarbitone on the CNS, CVS, and RS?

A

CNS: loss of consciousness + anticonvulsant

CVS: hypotension and tachycardia

RS: depression

45
Q

What is the use of Etomidate?

A

Alternative to thiopental or propofol for anesthetic induction in small animals, especially in patients with:

  • Preexisting cardiac dysfunction: minimal effects on the CVS
  • Head trauma
  • That are critically ill

note: may be used for immersion anesthesia in certain exotics e.g. frogs

46
Q

What are the risks or cautions associated with Etomidate?

A
  • Decreases Hypothalmic pituitary axis, thus inhibiting the conversion of cholesterol to cortisol, thus risking the patient to develop addisons disease
  • Can cause histamine release
  • Can cause paddling of the limbs during induction

Clinical Anesthesia (17 decks)

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