Anaesthesia

Question 1

What are the four stages of anaesthesia (Guedel’s signs)?

Answer 1

1. Analgesia (pt concious)
2. Unconciousness, erratic breathing, normal or increased muscle tone, +/- delerium
3. Surgical anaesthesia - decreasing muscle tone and resp rate
4. Resp paralysis, no muscle tone, death

Question 2

Name an inhalational/volatile anaesthetic

Answer 2

Xenon

Nitrous oxide

Question 3

How is the potency of inhalational anaesthesia described?

Answer 3

Minimum alveolar concentration (MAC) at which 50% of subjects fail to move to surgical stimulus

Question 4

What are the two drug factors affecting induction and recovery from anaesthesia? (How well the drug leaves the body)

Answer 4

• Solubility of the gas in the blood: less soluble means the drug wants to leave the blood
• Solubility of the gas in lipid: less soluble means it doesn’t want to stay in the tissues

Question 5

State two drug factors that effect the MAC (potency)

Answer 5

• Lipid solubility

- How well they promote GABA activity to inhibit neurones in the reticular formation (hind- and midbrain and thalamus)

Question 6

State two ways other drugs can affect the MAC

Answer 6

• Other anaesthetics (decreased) e.g. add N2O to another anaestheic to make the primary anaesthetic more potent
• Opioids (decreased)
• Central stimulants (increased)

Question 7

State three patient factors that affect the MAC

Answer 7

• Age (MAC lower in the elderly)
• Hyperthermia (increased)
• Hypothermia (decreased)
• Pregnancy (increased)
• Alcoholism (increased)

Question 8

Name two intravenous anaesthetics

Answer 8

Propofol
Barbituates
Ketamine

Question 9

How is the potency of intravenous anaesthetic measured?

Answer 9

Plasma concentration needed to achieve a specific end e.g. loss of eyelash reflex, or a bi-spectral index measure of cortical activity

Question 10

Name two local anaesthetics

Answer 10

Lidocaine
Bupivacaine
Ropivacaine
Procaine

Question 11

State two factors of local anaesthetics that effect its action

Answer 11

Higher lipid solubility => higher potency

Ester links are metabolised faster than amide links

Higher protein binding => longer duration

Lower pKa means that the anaesthetic is more likely to exist in its uncharged form at physiological pH, and therefore be able to diffuse into the nerve sheath

Question 12

How does the MoA of local anaesthetic allow it to work better in small myelinated pain fibres?

Answer 12

Use-dependant block of Na+ channels

Question 13

Name two nerves that can be blocked by regional anaesthesia to anaesthetise the upper limb

Answer 13

Interscalene
Supraclavicular
Infraclavicular
Axillary

Question 14

Name two nerves that can be blocked by regional anaesthesia to anaesthetise the lower limb

Answer 14

Femoral
Sciatic
Popliteal
Saphenous

Question 15

Name three side effects of anaesthesia

Answer 15

Post-op N+V

Post-op cognitive dysfunction (increased risk with age)

Chest infection from not moving or breathing a great deal

CVS depression can lead to hypotension