Anaesthetics

Question 1

Nitrous oxide, isoflurane, desflurane

Answer 1

Indication: volatile anaesthetics

Action:

• most potentiate GABAa receptors, cl- conductance
• Xe, N20 block NMDA receptors, Ca2+ conductance

Target:

• reticular formation - activating system
• thalamus - sensory
• hippocampus - memory
• brainstem - resp and CVS
• spinal cord - dorsal horn analgesia, motor neuronal activity

1. Low dose = memory
2. Consciousnes
3. Movement
4. High dose = cardiovascular response

MAC describes volatile potency = alveolar conc at which 50% of subjects fail to move to surgical stimulus
- spinal cord = anatomical site

Solubility effected by:

• blood:gas partition (low = fast induction and recovery)
• oil:gas partition (high = slow induction and recovery)

Potency:

• indirectly correlated to lipid solubility
• directly correlated to GABAa interaction

Nitrous oxide added to other volatile agents to reduce dosing and side effects

Question 2

Propofol, barbotuates, etomidate, ketamine

Answer 2

Indication: IV anaesthetics

Action:

• potentiate GABAa receptors, cl- conductance
• ketamine blocks NMDA receptors, Ca2+ conductance

Target:

• reticular formation - activating system
• thalamus - sensory
• hippocampus - memory
• brainstem - resp and CVS
• spinal cord - dorsal horn analgesia, motor neuronal activity

Side effects:

• emesis
• hypotension
• POCD
• chest infection

Question 3

Lidocaine, bupivacaine

Answer 3

Class: local anaesthetic

Action:

• block voltage gated sodium channels
• prevents propagation of action potentials
• USE dependent - firing channels blocked more efficiently
• block small myelinated nerves - nociceptive and symp block

Characteristics:

• increase lipid solubility = increase potency
• increase protein binding = increase duration
• lower pKa = faster onset
• ester link = fast metabolism, amide link = slow metabolism

Side effects:

• cardiovascular toxicity
• allergic reactions