Anaesthetics

Question 1

Outline the stages of anaesthesia

Answer 1

Premedication = benzodiazepine (calm)

Induction = intravenous/inhalational (sleep)

Intraoperative analgesia = opioid (pain)

Muscle paralysis = intubation/ventilation/stillness

Maintenance = intravenous/inhalational

Reversal of muscle paralysis/recovery/postoperative analgesia = opioid/NSAID/paracetamol)

Provision for nausea/vomiting

Question 2

Discuss inhalational anaesthetics (volatile)

Answer 2

E.g. N2O, chloroform, cyclopropane, halothane

Inert gas at high pressure = good anaesthetic

Question 3

Discuss IV anaesthetics

Answer 3

E.g. Propofol (rapid), barbiturates (rapid), ketamine (slower)

Can be used for induction or as sole anaesthetic

With exception of ketamine all potentiate GABA

Question 4

Outline Guedels signs

Answer 4

Signs to assess the depth of general anaesthesia

Stage 1: analgesia and consciousness

Stage 2: unconscious, breathing erratic but delirium could occur, leading to an excitement phase.

Stage 3: surgical anaesthesia, with four levels describing increasing depth until breathing weak.

Stage 4: respiratory paralysis and death 💤

Question 5

What is MAC?

Answer 5

Minimum Alveolar Conc = describes volatile potency

[Alveolar] (at 1atm) at which 50% of subjects fail to move to surgical stimulus

Question 6

What factors affect MAC?

Answer 6

Age = high in infants, low in elderly

Hyperthermia = increased

Preg = increased

Alcoholism = increased

Central stim = increased

Other anaesthetics = decreased

Opioids = decreased

Hypothermia = decreased

Question 7

What factors affect induction and recovery regarding anaesthetics?

Answer 7

Blood:gas partition = low value fast induction and recovery

Oil:gas partition = determines potency and slow accumulation due to partition in fat

Question 8

How do anaesthetics effect GABA?

Answer 8

With the exception of Xe, N2O and ketamine all anaesthetics potentiate GABA activity = major inhibitory transmitter

Depress CNS activity = decreased reticular formation (arousal), thalamus (sensory), hippocampus (memory), brainstem (resp, CVS), spinal cord (motor)

Question 9

Give examples of local anaesthetics

Answer 9

Lidocaine

Bupivacaine = wound analgesia

Ropivacaine

Procaine

Question 10

Describe the use of regional anaesthetics

Answer 10

Block the nerve, but pt still awake

Extradural/intrathecal/combined

Esters = short acting

Amides = longer acting

Question 11

Describe the side effects of anaesthetics

Answer 11

General = post-op nausea/vomiting, hypotension, cognitive dysfunction, chest infection

Local/regional = cardio toxicity, allergic reactions, anaphylaxis

Question 12

Outline the range of physiological variables monitored during surgery

Answer 12

BP

HR

Temperature

Pain

Consciousness