IV induction agents

Question 1

Induction doses:
- Propofol
- Thiopentone
- Ketamine
- Midazolam

Answer 1

(always reduce doses for elderly or sick patients)
Propofol: 1-2mg/kg (or TCI uses ~4-6mcg/mL, sedation requires 1-2mcg/mL). Very unwell patients in hypovolaemic shock you may only need 10-20mg of propofol to induce anaesthesia
Thiopentone: 3-5mg/kg
Ketamine: 1-2mg/kg
Midazolam: 0.05-0.1mg/kg

Question 2

Special features of IV induction agents

Answer 2

Propofol: Fast onset, smooth wake up, decrease PONV

Thiopentone: Fastest onset +++, only occassionally used these days if rare allergy to propofol, for ECT, or for neuroprotection by decreasing the brains metabollic rate and to decrease intracranial pressure

Ketamine: Fast onset, cardiostable, preserves resp, analgesia. It is a dissociative anaesthetic so less clear when pt is unconscious as eyes may still be open and moving

Midazolam: Cardiostable, large therapeutic range

Question 3

Main action of IV induction agents

Answer 3

Propofol: Hypnosis, GABA receptor

Thiopentone: Hypnosis, GABA receptor

Ketamine: Hypnosis, analgesia, NMDA antagonist

Midazolam: Hypnosis, GABA receptor

Question 4

Main side effects of IV induction agents

Answer 4

Propofol: CVS +++, resp depression

Thiopentone: CVS+++, resp depression, slower wake up

Ketamine: hallucinations, excess salivation, slow wake up

Midazolam: slower onset, lower efficacy

Question 5

Ketamine analgesia dose

Answer 5

0.05-0.2mg/kg/hr in syringe driver for intra-operative analgesia