S7.2 Anaesthetics

Question 1

What are the two classes of anaesthetics?

Answer 1

Gases (volatile): (delivered via lungs) e.g xenon, N2O

Intravenous: propofol, barbiturates, ketamine

Question 2

Explain the 4 different Guedel’s signs

Answer 2

Stage 1: analgesia and consciousness
Stage 2: unconscious, breathing erratic
Stage 3: surgical anaesthesia given, with four levels describing decreasing breathing and muscle tone.
Stage 4: respiratory paralysis and death

Question 3

What is volatile anaesthetic potency and how is it measured?

Answer 3

Concentration of a drug which produces a response.
VAC is described by Minimum Alveolar Concentration: alveolar conc at which 50% of subjects fail to move to surgical stimulus.

Question 4

What Factors affect Induction and Recovery?

Answer 4

Partition coefficients.
If blood:gas partition is low, shall have fast I and R
Oil:Gas partition (in fat) determines potency and slow accumulation due to partition into fat (obese patients take longer to wake up).

Question 5

What factors effect Minimum Alveolar Concentration?

Answer 5

Age (High in infants lower in elderly), Hyperthermia (high); hypo (low), Pregnancy and alcoholism (high), other anaesthetics and Opioids (low)

Question 6

Why do anaesthetics work on GABA receptors?

Answer 6

They are the major inhibitory transmitter. They have LGIC; Cl- enters hyperpolarising the cell stopping CNS activity.
Most anaesthetics potentiate GABA mediated Cl-conductance to depress CNS activity.

Question 7

Which systems in the brain are effected by anaesthetics?

Answer 7

Reticular formation depressed (no communication within brain). 
Hippocampus depressed (memory lost).
Brainstem depressed (respiratory and CVS reduced).
Spinal cord depressed (analgesia; dorsal horn) and motor neuronal activity (MAC).

Question 8

Name some local anaesthetics?

Answer 8

Lidocaine, Bupivacaine, Ropivacaine and Procaine

Question 9

What are the common characteristics of local anaesthetics?

Answer 9

Higher Lipid solubility - higher potency

Lower pKa - faster onset
Higher Protein binding – longer duration of action

Question 10

Describe how bupivicaine is used for wound analgesia?

Answer 10

Bupivicaine is not charged so can pass through plasma memb, and depending on its pKa, it shall become charged and get sucked into the VG Na channel, blocking pain action potentials firing

Question 11

What is regional anaesthesia?

Answer 11

Selectively anaesthetising a part of the body by blocking a nerve

Question 12

What are the ADRs of anaesthetics?

Answer 12

General: nausea, hypotension, delirium

Local and regional: cardiovascular toxicity