General Anaesthesia

Question 1

What is the purpose of GA?

Answer 1

To produce unconsciousness and a lack of responsiveness to all painful stimuli.

Question 2

What is the triad of GA effects?

Answer 2

1. Analgesia
2. Amnesia
3. Hypnosis

Question 3

What are the 5 steps of GA administration?

Answer 3

1. Pre-assessment
2. Induction
3. Maintenance
4. Reversal
5. Post-anaesthesia care

Question 4

State 5 features of the ideal GA.

Answer 4

unconsciousness, analgesia, muscle relaxation, amnesia, brief and pleasant, depth easily controlled, minimal adverse effects, large margin of safety

Question 5

In inhalation GAs, the higher the blood solubility, the (faster/slower) the onset?

Answer 5

slower

Question 6

Name and classify the 6 inhalation anaesthetics.

Answer 6

Volatile liquids (Halothane, Enflurane, Desflurane, Isoflurane, Sevoflurane)
Gases (Nitrous oxide)

Question 7

What is Minimum Alveolar Concentration?

Answer 7

The minimum concentration of drug in alveolar air that will produce immobility in 50% of patients exposed to pain.

Question 8

Describe the allosteric modulation of inhalation GAs.

Answer 8

• positive allosteric modulation: allosterically increasing GABA receptor sensitivity
• negative allosteric modulation: blocking glutamate neurotransmitter acting on NMDA receptor

Question 9

Describe the ADME of inhalation GAs.

Answer 9

A: increases with higher concentration of anaesthetic in inspired air, increased solubility of GA, and increased blood flow through lungs
D: highly perfused organs have better distribution
M: metabolites can be toxic
E: eliminated via the lungs with minimal hepatic metabolism

Question 10

Which inhalation GAs have toxic metabolites?

Answer 10

• nephrotoxic: Isoflurane, Enflurane
• hepatotoxic: Halothane

Question 11

Describe intravenous GAs.

Answer 11

• usually induction agents
• induce unconsciousness but don’t maintain it
• usually depress respiration
• used alone or to supplement inhalation anaesthetics
• reduce barbiturate use (thiopentone) because of the risk of addiction and death

Question 12

What are the 4 types of anaesthetic adjuncts?

Answer 12

• Benzodiapines (Midazolam): for sedation
• Alpha-2 Adrenergics (Dexmedetomidine): for sedation and analgesic effects
• Opioid Analgesics (Fentanyl): for pain relief in perioperative period
• Neuromuscular blockers (Succinylcholine, Vecuronium): to relax and immobilise muscles

Question 13

Describe Halothane effects and adverse effects.

Answer 13

Effects: relaxes skeletal muscle, enhance skeletal muscle relaxants (little or no analgesia until unconsciousness)
Adverse effects: respiratory depression (dose dependent), depression of cardiac output causes bradycardia and arrhythmia, halothane-associated hepatitis

Question 14

Describe the characteristics of Nitrous Oxide.

Answer 14

• odourless gas
• non-flammable
• rapid onset and recovery but not potent (analgesia and amnesia but not complete unconsciousness)
• supplements other GAs or used for analgesia only
• adverse effects include post-op nausea and vomiting

Question 15

Describe the features of Sodium Thiopental or Thiopentone.

Answer 15

• barbiturate with high lipid solubility
• MOA: potentiates GABA action on GABA(A) chloride ion channels, causing hyperpolarization
• enters the brain easily and rapidly, distributes well to less vascularized tissue
• forms an active metabolite that can cause liver cirrhosis
• slow elimination as it is extensively bound to plasma proteins

Question 16

Describe the uses and effects of Propofol.

Answer 16

• used for induction and maintenance (e.g. for day surgery)
• anti-emetic and reduces post-op vomiting
• rapid onset, short duration of action, rapid redistribution from brain to tissues
• causes hypotension, bradycardia (hence contraindicated in elderly patients, compromised cardiac function, low blood vol)

Question 17

Describe the effects and adverse effects of Ketamine.

Answer 17

• produces dissociative anaesthesia, sedation, immobility, analgesia, amnesia (patient loses responsiveness to pain)
• rapid induction and large Vd
• metabolised in liver and excreted in urine and blood
• May cause hallucinations, disturbing dreams or delirium post-op (reduce with pre-medication of diazepam or midazolam)