Outline the pharmacological properties of an ideal agent for sedating patients
undergoing mechanical ventilation in intensive care (50% of marks). Describe how
propofol compares to the ‘ideal’ agent (50% of marks).

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College Answer

Candidates can benefit by having a system by which they approach topics that involve a
broad and general topic such as that of the pharmacology of a particular drug or ideal agent.
A good answer included the following logical subheadings:
Desirable pharmacology – long shelf life, stable when drawn up and on exposure to light,
cheap, mixes well with other agents in the central line lumen. Bacteriostatic.
Desirable pharmacokinetics – Low volume of distribution, rapid clearance (context-sensitive
half-life), clearance not affected by either renal or hepatic dysfunction. Little inter-individual
variation in pharmacokinetics. (Availability of an antagonist).
Desirable pharmacodynamics – Affects only CNS. Reliable dose – effect curve with little
inter-individual variation in effect. Anxiolysis. (Analgesic properties). No effect on
cardiovascular performance. Does not depress respiratory drive.
Minimal side effects – No incidences of allergy / anaphylaxis. No idiosyncratic reactions. No
tachyphylaxis.
As indicated, 50% of the marks were allocated to mentioning how well propofol reflects
these properties. Mention of ‘propofol infusion syndrome’ characterised by cardiac failure which can occur when propofol is used at >4mg/Kg/Hr for more than 24 hours also attracted marks.
Syllabus: G2a 1&2
Reference Text: Pharmacology and Physiology in Anesthetic Practice / R K Stoelting