General Anaesthesia

Question 1

What is general anaesthetics

Answer 1

Reversible drug induced loss of consciousness, usually to allow a surgical procedure to be preformed

Question 2

What are some of the common IV induction agents

Answer 2

Propofol, thiopentone, etomidate

Question 3

Name some of the inhalation anaesthetics agents and their uses

Answer 3

Nitrous oxide, isoflurane, sevoflurane or desflurane.

They can be used to induce anaesthesia (children) but more commonly maintain anaesthesia.

Question 4

When might you use entonox?

Answer 4

(it is a 50:50 nitrous oxide/oxygen mix) This can be used for analgesic, labour or trauma. However going out of fashion as it is a greenhouse gas and other health concerns

Question 5

Describe features of inhalation agents if they are more lipid/blood soluble (theory of overton and meyer)

Answer 5

• The more lipid soluble then the more potent the gas and therefore lower the MAC (minimum alveolar concentration)
• The more blood soluble the agent is then the slower the onset of unconsciousness

Question 6

Explain the pharmacodynamics of general anasthetics

Answer 6

• Activate inhibitory channels such as GABA (and others).

- Inhibit excitatory channels such as NMDA receptors

Question 7

Explain the mechanism of etomidate, propofol and barbituates

Answer 7

• They will excite GABA(A) receptors which will inhibit neuronal excitability.

Question 8

What is the mechanism of volatile anaesthetics?

Answer 8

• Excite GABA(A) receptors,
• Inhibit sodium channels which prevents neuronal excitability and excitatory neuro-transmission.
• Excite background potassium channels which inhibits neuronal excitability and excitatory neuro-transmission.

Question 9

What are the mechanisms of nitrous oxide or xenon?

Answer 9

• Activate background potassium channels which inhibits neuronal excitability and inhibits excitatory neuro-transmission.
• Inhibit NMDA receptors which prevents excitatory neuro-transmission

Question 10

What is the mechanism of ketamine?

Answer 10

Inhibits NMDA receptors which prevents excitatory neuro-transmission

Question 11

What are some issues of ketamine?

Answer 11

• Class B drug which is increasingly misused.

- It can cause bladder problems and dissociative (K-hole)

Question 12

What do we WANT / NOIT WANT anaesthetic agents to do?

Answer 12

Act rapidly, pleasant, cheap to manufacture, stable, analgesic effect, amnesic affect and to have minimal hangover.
We do not want them to irritate veins or airways, not to be emetic agents, and have minimal effects on other systems

Question 13

Compare three IV anaesthetic agents

Answer 13

Thiopentone, propofol and etomidate.
All will reduce resp rate. Thiopentone and propofol will reduce ICP. Propofol will markedly reduce BP, reduce cardiac output and is painful upon injection.
Thiopentone will will reduce BP and cardiac output but not as much as propofol but is not painful on injection.
Etomidate is best for unstable patients as it doesn’t affect BP, cardiac output, heart rate, SVR or ICP but is painful on injection.

Question 14

What agent will not reduce respiratory rate?

Answer 14

Ketamine

Question 15

Compare three inhaled anaesthetics

Answer 15

Isoflurane, Desflurane and sevoflurane.

All reduce respiratory rate and tidal volume and increase PaCO2.
Heart rate - Increased in I and D but not in S.
Systemic vascular resistance reduced in all, blood pressure reduce in all.
All increase cerebral blood flow, all relax uterus and have significant muscle relaxation.
Desflurane is better for overweight patients as they wake up quickly. Sevoflurane has a smaller effect than others.

Question 16

What is balanced anaesthesia?

Answer 16

A selection of drugs and techniques to minimise patient risk and maximise patient safety and comfort whilst bearing in mind health and requests of patient, properties of the drugs and requirement of surgery.