General Anaesthetics

Question 1

What are the two broad types of anaesthesia

Answer 1

1. General anaesthesia - makes patient unconscious
2. Local/regional - blocks feeling to localised region e.g. limb

Question 2

Fasting before GA
1. Purpose
2. When is the patient at highest risk of aspiration
3. Major causes of morbidity/mortality in anaesthetics
4. Fasting time-frames

Answer 2

1. empty stomach = reduced risk of reflux = reduced risk of aspiration pneumonitis
2. Before and during intubation, and when they are extubated (once the endotracheal tube is correctly fitted, the airway is blocked and protected from aspiration)
3. Aspiration pneumonitis and pneumonia
4. 6 hours of no food or feeds before the operation
   2 hours of no clear fluids (fully “nil by mouth”)

Emergency –> RSI (rapid-sequence induction)

Question 3

Preoxygenation
1. What is it
2. What physiological measure of spirometry is it relevant to

Answer 3

1. Before GA, patient on 100% O2 –> O2 reserve for period between loss of consciousness and intubation + ventilation.

Emergency –> may be skipped

2. Functional reserve capacity - the volume remaining in the lungs after a normal, passive exhalation

Question 4

Premedication
1. Purpose
2. Examples (BOA)

Answer 4

1. relaxation, reduce anxiety, reduce pain and make intubation easier

Benzodiazepines (e.g., midazolam) –> muscle relaxation + reduce anxiety (also causes amnesia)

Opiates (e.g., fentanyl or alfentanyl) –> reduce pain and reduce the hypertensive response to the laryngoscope

Alpha-2-adrenergic agonists (e.g., clonidine), which can help with sedation and pain

Question 5

Rapid Sequence Induction/Intubation (RSI)
1. What is it
2. Why is it higher risk than normal intubation
3. What are its uses non-emergency
4. What is the single highest risk of RSI
5. How can you reduce the risk of 4.

Answer 5

1. Gain airway control quickly and safely in emergency scenario using an ET tube as soon as possible after induction (patient unconscious)
2. • No fasting
   • No pre-planning e.g. difficult airway

3.GORD or pregnancy

4. Aspiration

5.
1. more upright bed
2. Cricoid pressure?

Question 6

Hypnotic agents
1. What is their use
2. How can they be delivered to the patient

Answer 6

1. Make patient unconscious
2. IV or inhaled

Question 7

What is the triad of general anaesthesia (HMA)

Answer 7

Hypnosis
Muscle relaxation
Analgesia

Question 8

Examples of IV hypnotic agents (PKTE)

Answer 8

Propofol (the most commonly used)
Ketamine
Thiopental sodium (less common)
Etomidate (rarely used)

Question 9

Examples of inhaled hypnotic agents (SDI fluranes + NO)

Answer 9

Sevoflurane (the most commonly used)
Desflurane (less favourable as bad for the environment)
Isoflurane (very rarely used)
Nitrous oxide (combined with other anaesthetic medications – may be used for gas induction in children)

Question 10

1. What characteristic do sevoflurane, desflurane and isoflurane share in common?
2. What device is used to deliver these agents?

Answer 10

1. All are volatile anaesthetic agents i.e. liquid at room temperature and need to be vaporised into a gas to be inhaled.
2. Vaporiser (liquid poured into and turned to vapour mixed with air –> conc can be altered to control depth of anaesthesia)

Question 11

Which agent is usually given first (IV or inhaled)?
1. Why
2. What is TIVA?

Answer 11

IV to induce, inhaled to maintain
1. IV acts quicker, while inhaled must diffuse across lung tissue until ideal concentration is reached
2. TIVA = Total intravenous anaesthesia i.e. IV used throughout (easier wake up)

Question 12

Muscle relaxants (Neuromuscular blockers)
1. MoA
2. Types
3. How to reverse

Answer 12

1. Block nicotinic N1 receptors in neuromuscular junctions, preventing skeletal muscle stimulation –> relax and paralyse muscle –> intubation is easier
2. Depolarising - suxamethonium
   Non-depolarising - Rocuronium, atracurium
3. Cholinesterase inhibitors e.g. neostigmine

Question 13

What is Sugammadex

Answer 13

Used specifically to reverse the effects of certain non-depolarising muscle relaxants (rocuronium and vecuronium)

Question 14

Adverse effects of volatile anaesthetic agents

Answer 14

• Myocardial depression
• Malignant hyperthermia
• Halothane (not commonly used now) is hepatotoxic

Question 15

Adverse effects of nitrous oxide

Answer 15

May diffuse into gas-filled body compartments → increase in pressure → avoid in pneumothorax

Question 16

Mechanism of action of propofol, thiopental sodium and etomidate

Answer 16

Potentiate GABAa

Question 17

MoA of ketamine

Answer 17

NMDA antagonist

Question 18

Adverse effects of propofol

Answer 18

• Pain on injection (TRPA1 activation)
• Hypotension

Question 19

Adverse effects of thiopental sodium

Answer 19

• Laryngospasm
• Unsuitable for maintenance –> metabolites build up quickly

Question 20

Adverse effects of etomidate

Answer 20

• Unsuitable fo rmaintenance –> primary adrenal suppression (reversible binding to 11 β-hydroxylase)
• Myoclonus
• Common post-op N&V

Question 21

Adverse effects of ketamine

Answer 21

• Disorientation
• Hallucinations

Question 22

Advantages of propofol

Answer 22

• Rapid onset of anaesthesia
• Suitable for maintenance –> rapidly metabolised with no build-up
• Anti-emetic

Question 23

Advantages of thiopental sodium

Answer 23

Extremely rapid onset of action making it the agent of choice for rapid sequence of induction

Question 24

Analgesia: most commonly used in anaesthetics

Answer 24

Fentanyl
Alfentanil
Remifentanil
Morphine

Question 25

Key considerations for emergence 1. TOF 2. Sites of stimulation 3. What happens when relaxant has worn off

Answer 25

1. Train-of-four (TOF) stimulation, nerve stimulation four consecutive times - muscle contraction strong --> worn off - gets weaker with additional stimulation --> not fully worn off --> "awareness under anaesthesia" if woken early 2. A. ulnar nerve at the wrist, watching for thumb movement (twitches) B. facial nerve (movement in the orbiculares oculi muscle at the eye) 3. Stop inhaled anaesthetic, patient will regain consciousness, extubated at the point where they are breathing for themselves.

Question 26

Risks of GA

Answer 26

Common: sore throat and PONV Significant: - Accidental awareness (waking during the anaesthetic) - Aspiration - Dental injury, mainly when the laryngoscope is used for intubation - Anaphylaxis - Cardiovascular events (e.g., myocardial infarction, stroke and arrhythmias) - Malignant hyperthermia (rare) - Death

Question 27

Malignant Hyperthermia: what is it

Answer 27

1. rare but potentially fatal hypermetabolic response to anaesthesia

Question 28

Malignant hyperthermia: anaesthetic agents that are at higher risk of causing it

Answer 28

2. Volatile + suxamethonium

Question 29

Malignant hyperthermia: genetic mutations + pattern of inheritance

Answer 29

3. RYR1 (mostly) and CACNA1S mutations increase risk of MH --> autosomal dominat

Question 30

Malignant hyperthermia: presentation

Answer 30

- Increased body temperature (hyperthermia) - Increased carbon dioxide production - Tachycardia - Muscle rigidity - Acidosis - Hyperkalaemia

Question 31

Malignant hyperthermia: treatment

Answer 31

Dantrolene - interrupts the muscle rigidity and hypermetabolism by interfering with the movement of calcium ions in skeletal muscle.