Pharmacodynamics and Pharmacokinetics of Propofol

Induction Agents

• Etomidate is preferred in shock, for long procedures, or when extra analgesia is important.
• Ketamine is good in haemodynamically unstable patients, but it's not available in Australia.
• Propofol is good for haemodynamically stable patients or short procedures.

Properties of Induction Agents

• Ketamine has excellent amnesic properties.
• Ketamine has bronchorelaxant properties, making it useful in critical asthma, but it also increases bronchial secretions.
• Ketamine is best for longer, painful procedures, particularly in children.

Ketamine

• The duration of action of ketamine when administered intravenously is 10-15 minutes.
• One adverse effect associated with ketamine administration is hallucinations.
• The usual dose of ketamine for induction of anaesthesia intravenously is 1-2 mg/kg.
• The change in scheduling for ketamine from Schedule 4 to 8 in 2005 was due to its abuse potential.
• Ketamine causes the patient's eyes to become dilated and unreactive.
• The mechanism of action of ketamine as an analgesic is NMDA receptor antagonism.
• In children under 2 years of age, ketamine administration is associated with increased secretions and respiratory problems.
• The most common cardiovascular effect of ketamine administration is increased heart rate and blood pressure.
• If the total intravenous dose of ketamine exceeds 5 mg/kg, it can cause respiratory depression.

Propofol

• The primary mechanism of action of propofol in altering neuronal function is GABA receptor activation.
• The most significant route of metabolism for propofol in the body is liver metabolism.
• The approximate half-life of distribution for propofol is 2-8 minutes.
• The primary reason for the anti-emetic effect of propofol is its antagonism of dopamine receptors.
• The usual dose of propofol for induction of anaesthesia in adults is 1-2 mg/kg.
• Propofol-related infusion syndrome is associated with cardiovascular and metabolic acidosis.
• The main disadvantage of using propofol is its cost.

Etomidate

• The distribution half-life of etomidate is 2-5 minutes.
• The duration of effect of etomidate is 3-5 minutes.
• Up to 70% of cases of etomidate administration are associated with myoclonus.

Remifentanil

• The main advantage of using remifentanil is its rapid onset and offset of action.
• Remifentanil is metabolized by esterases in the blood.

Fentanyl

• Fentanyl is specially used in hypovolaemic conditions due to its vasopressor effects.
• If the total intravenous dose of ketamine exceeds 5 mg/kg, it can cause respiratory depression.