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Anaesthesia- MBChB Year 4 > IV Induction Agents > Flashcards

IV Induction Agents Flashcards

1
Q

WHAT IS AN INDUCTION AGENT?

A

Produces loss of consciousness within one arm-brain time–> approximately 30 seconds
Induction agents induces anaesthesia

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2
Q

List 4 rapidly acting, true IV induction agents

A

Thiopentone
Etomidate
Propofol
Ketamine

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3
Q

List 3 slower acting IV induction agents

A

Benzodiazepines
Neuroleptic-anaesthetics
Opioids

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4
Q

What are the benefits of IV agents?

A

Rapid onset of action
More pleasant & acceptable for the patient
Pollution free
Low incidence of side-effects
Smooth induction with rapid transfer through the classic stages of anaesthesia

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5
Q

What are the disadvantages of IV agents

A

Requires intravenous access
It is easy to give too much …. side-effects
No removal of drug via the lungs as with inhalationals
-Recovery requires
*Redistribution
*Metabolism
*Excretion
Sudden loss of normal protective reflexes

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6
Q

Explain the mechanism of action for IV agents.

A

Most sedative hypnotics exert their effect via the inhibitory GABAA receptors
GABA – γ (gamma)-aminobutyric acid
Increased chloride conductance → hyperpolarisation → neuronal inhibition
Some inhibit the release of glutamate, an excitatory amino acid, in brain

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7
Q

Explain the pharmacokinetics of intravenous anaesthetics

A

The onset of action depends on the drug reaching the effect site (the brain) by crossing the Blood-Brain Barrier
Arm-brain circulation time is determined by:
Speed of injection
Lipid solubility
Protein binding
Blood flow to brain

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8
Q

List the characteristics of the ideal IV induction agent

A 
Smooth and rapid onset of action 
Inexpensive 
Rapid recovery 
Minimal side effects 
No pain on injection
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9
Q

How would one reduce pain on injection?

A

IV lignocaine 10-20mg when giving propofol

New, large bore free running IV line

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10
Q

What are the international colour codings for all true IV induction agents and IV sedatives.

A

Yellow for true IV induction agents

Orange for IV sedatives

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11
Q

What are the physical properties of propofol?

A

It is hydrophobic 1%. Also known as 2,6 di-isoprophylphenol.
Most commonly used IV induction agent

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12
Q

Pharmacodynamics of Propofol

A

Can be infused for long periods with rapid emergence. Sequesters in fat

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13
Q

Effects of Propofol on the CNS

A

Rapid loss of consciousness and rapid recovery (3-6 min. Complete in 3 hours)
Less hangover.
No antanalgesia, no analgesic
Antipruritic

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14
Q

Effects of propofol on the CVS

A

Cardiovascular depression. Less compensatory tachycardia = greater hypotensive effect

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15
Q

Effects of propofol on the respiratory system

A

Respiratory depression with 100% incidence of apnoea, depresses laryngeal reflexes. Does not release histamine.

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16
Q

Indications for propofol

A 
Porphyria
Asthma
Day-case
Conscious sedation 
Hx of malignant Hyperthemia
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17
Q

Contraindications for propofol

A

Avoid in elderly, heart failure, hypovolaemia, fixed cardiac output

18
Q

Physical properties of thiopentone

A

Barbiturate, precipitates when mixed with muscle relaxants. 2.5%

19
Q

Pharmacodynamics of thiopentone

A

Long elimination half-life – induction only
3-5mg/kg in adults

Children: 5-6mg/kg

Caution in elderly

20
Q

CNS effects of thiopentone

A 
Rapid LOC (30 seconds)  Recovery 5-10 min. antanalgesia. Anticonvulsant
Possible protection with decreased cerebral metabolic rate and intracranial pressure
21
Q

CVS effects of thiopentone

A

Decreases cardiac output – peripheral vasodilation, negative inotropic effect, decrease in central catecholamine release. Compensatory tachycardia. CVS depression exaggerated in heart failure, hypovolaemia, fixed cardiac output

22
Q

Resp effects of thiopentone

A

Potent depressant. Laryngeal reflexes not depressed until deeply anaesthetised. Histamine release and active respiratory reflexes = avoid in asthmatics

23
Q

Oher effects of thiopentone

A

Irritant to tissues – venous thrombosis. Intra-arterial injection = precipitation

24
Q

Indications for thiopentone

A

Golden standard

25
Q

Contraindications for thiopentone

A

Porphyria, known allergy, CVS disorders, asthma

26
Q

Etomidate- Physical properties

A

2mg/ml – mix to 1 mg/ml

27
Q

Pharmacodynamics of etomidate

A

Repeated doses not cumulative. Not used as infusion because of adrenal cortical depression
Induction: 0.2-0.3mg/kg

28
Q

Etomidate- CNS effects

A

Rapid onset. Rapid recovery 6-8 min. high incidence of involuntary movements and myoclonus – reduced by opiates and midazolam

29
Q

Etomidate- CVS effects

A

Very stable, may cause bradycardia when mixed with opioids and sux.

30
Q

Etomidate- Resp effects

A

Very little respiratory depression No release of histamine.

31
Q

Etomidate- Metabolic effects

A

Inhibits cortisol and aldosterone synthesis

32
Q

Etomidate- Pain on injection? Yes/no?

A

Yes

33
Q

Etomidate- Indications

A

Cardiac Patient s

34
Q

Ketamine- Physical properties

A

10mg.ml and 100 mg/ml. acidic. IV, intramuscular and oral. Derived from phencyclidine

35
Q

Ketamine- Pharmacodynamics

A

50-60% of drug remains after recovery – protracted emergency
Induction: 1-2 mg/kg onset 30-60 sec. lasts 5-15 min
Maintenance – 0.5mg/kg boluses, 1-4mg/kg/hr infusion.
Analgesia 0.2-0.4mg/kg IM followed by 0.2-0.3 mg/kg/hr infusion.

36
Q

Ketamine- CNS effects

A

Dissociative anaesthetic – complete analgesia and amnesia. Involuntary movements, nystagmus, vocalisation. Psychic reactions – hallucinations. Place in darkened area. Tolerance.

37
Q

Ketamine- CVS effects

A

Raise in BP, pulse, peripheral resistance, CO. Dysrrhythmias due to stimulation of central catecholamine release. Myocardial depressant.

38
Q

Ketamine- Resp Effects

A

Minimal respiratory depression. Pharyngeal reflexes are preserved with good airway control. Bronchodilation. Increase in secretions – administer with antisialogogue

39
Q

Ketamine- GIT effects

A

Post operative N&V

40
Q

Ketamine- other effects

A

Uterine contraction in first trimester

41
Q

Ketamine- indications

A

Poor risk surgical patients, paediatric surgery, debridement, painful dressings or skin grafts, short procedures, analgesia, field-work, status asthmaticus

42
Q

Ketamine Contraindications

A

Aspiration risk. Shock, hypertension, IHD, aortic aneurysms, severe heart failure, raised ICP, cerebral aneurysms, open eye injuries, increased intraocular pressure, psychiatric patients, epileptics, thyrotoxicosis. Early pregnancy

Anaesthesia- MBChB Year 4 (5 decks)

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