IV Agents

Question 1

Classifications of IV anesthesia & name agents in each class

Answer 1

Rapid Acting - 4
Propofol,
Ketamine,
Etomidate,
Thiopentone

Slower Acting - 3
BDZ - Diazepam, Midazolam
Neuroleptics - Haloperidol, Droperidol
Opioids - Fentanyl, sufentanil, remifentanil, alfentanil, morphine

Question 2

Advantages of intravenous induction

Answer 2

1. Rapid onset of action
2. Smooth induction with rapid transfer through stage II (stage of excitement)
3. More pleasant for the patient
4. Pollution free

Question 3

Disadvantages of intravenous induction

Answer 3

1. Venepuncture required
2. Overdose easy
3. No removal of drug via the lungs (as with inhalational agents). Once it’s in, it’s in; there is no going back (cf. the inhalational agents that can be switched off to reverse the effect). Recovery requires redistribution, metabolism and excretion.
4. Sudden loss of normal protective mechanisms and often apnoea.

Question 4

What causes termination of IV drug effects?

Answer 4

The termination of the action of the IV induction agents is due to redistribution of drug from the brain to less well-perfused tissues, i.e. the drug is mobilised from the tissues where it is initially deposited because of their rich blood supply, to tissues of poorer blood supply. The reason the patient awakens after a number of minutes is due to this redistribution of drug from the brain. Rapid awakening is not due to metabolism or excretion of the drug.

Question 5

Warnings for IV agents post op

Answer 5

Sub-anaesthetic concentrations may persist in the brain for some time, and may impair function of higher centres required for driving or operating machinery. This also increases sensitivity to sedatives, analgesics and alcohol.
Patients must be cautioned about partaking in these activities or taking any legally binding decisions for at least 24 hours after even the shortest general anaesthetic.

Question 6

How are IV agents excreted?
What effects excretion rate?

Answer 6

These lipid-soluble drugs are metabolised in the liver to inactive water-soluble metabolites; then excreted in the urine.

The importance of metabolism and excretion terminating the drug effect increases with high plasma concentrations due to multiple doses or continuous IV infusion.