IV Induction Agents Flashcards by Nugh Samsodien

WHAT IS AN INDUCTION AGENT?

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

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List 4 rapidly acting, true IV induction agents

Thiopentone
Etomidate
Propofol
Ketamine

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List 3 slower acting IV induction agents

Benzodiazepines
Neuroleptic-anaesthetics
Opioids

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What are the benefits of IV agents?

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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What are the disadvantages of IV agents

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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Explain the mechanism of action for IV agents.

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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Explain the pharmacokinetics of intravenous anaesthetics

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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List the characteristics of the ideal IV induction agent

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

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How would one reduce pain on injection?

IV lignocaine 10-20mg when giving propofol

New, large bore free running IV line

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

Yellow for true IV induction agents

Orange for IV sedatives

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What are the physical properties of propofol?

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

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Pharmacodynamics of Propofol

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

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Effects of Propofol on the CNS

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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Effects of propofol on the CVS

Cardiovascular depression. Less compensatory tachycardia = greater hypotensive effect

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Effects of propofol on the respiratory system

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

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Indications for propofol

Porphyria
Asthma
Day-case
Conscious sedation 
Hx of malignant Hyperthemia

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Contraindications for propofol

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

Physical properties of thiopentone

Barbiturate, precipitates when mixed with muscle relaxants. 2.5%

Pharmacodynamics of thiopentone

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

Children: 5-6mg/kg

Caution in elderly

CNS effects of thiopentone

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

CVS effects of thiopentone

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

Resp effects of thiopentone

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

Oher effects of thiopentone

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

Indications for thiopentone

Golden standard

Contraindications for thiopentone

Porphyria, known allergy, CVS disorders, asthma

Etomidate- Physical properties

2mg/ml – mix to 1 mg/ml

Pharmacodynamics of etomidate

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

Etomidate- CNS effects

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

Etomidate- CVS effects

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

Etomidate- Resp effects

Very little respiratory depression No release of histamine.

Etomidate- Metabolic effects

Inhibits cortisol and aldosterone synthesis

Etomidate- Pain on injection? Yes/no?

Yes

Etomidate- Indications

Cardiac Patient s

Ketamine- Physical properties

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

Ketamine- Pharmacodynamics

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.

Ketamine- CNS effects

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

Ketamine- CVS effects

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

Ketamine- Resp Effects

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

Ketamine- GIT effects

Post operative N&V

Ketamine- other effects

Uterine contraction in first trimester

Ketamine- indications

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

Ketamine Contraindications

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