GA

Question 1

What is General Anaesthesia used for?

Answer 1

To produce
1. unconsciousness
2. lack of responsiveness
to all painful stimuli (inhibition of sensory or autonomic reflexes)

Question 2

General anaesthesia stages (6)

Answer 2

1. Pre-assessment/Premed
2. Induction
3. Airway management
4. Maintenance of anaesthesia
5. Reversal/emergency
6. Post-operative care

Question 3

Ideal properties of GA (8)

Answer 3

1. unconsciousness
2. analgesia
3. muscle relaxation (inhibit reflex)
4. amnesia
5. brief & pleasant
6. depth of anaesthesia can be altered easily
7. minimal adverse effects
8. margin of safety large

Question 4

Triad for balanced anaesthesia

Answer 4

1. pain relief
2. reflex inhibition
3. unconsciousness (induction)

Question 5

Why is there a need for balanced anaesthesia?

Answer 5

To ensure smooth and rapid induction & that analgesia and muscle relaxation are adequate

Question 6

Types of GA (2)

Answer 6

1. Inhalation anaesthetics

2. IV anaesthetics

Question 7

Inhalation GA (3+1)

Answer 7

Volatile liquids

1. Halothane
2. Isoflurane (pungent)
3. Sevoflurane

Gasesous
1. Nitrous oxide

Question 8

MOA of inhalation GA (2)

Answer 8

1. Enhance neurotransmission at inhibitory synapse via allosterically, increasing GABA receptors sensitivity to GABA itself (positive allosteric modulation)
2. Depress neurotransmission at excitatory synapse via blocking glutamate neurotransmitter acting on NMDA receptors, prevent activation of NMDA receptors (negative allosteric modulation)

Question 9

MAC

Answer 9

Minimum Alveolar Concentration

• index of INHALATION anaesthetic potency
• minimum concentration in alveolar air that will produce immobility to 50% of patients exposed to a painful stimulus
• decrease MAC = increase potency
• MAC alters with age, condition and concurrent drug use

Question 10

Factors affecting absorption of inhalation GA

Answer 10

1. conc of anaesthetic in inhaled air
2. blood perfusion of lungs
3. solubility of anaesthetic in blood

increase means increase absorption

BUT
increase solubility in blood means slower onset of action

Question 11

Factors affecting distribution of inhalation GA

Answer 11

• perfusion of organ/tissue

highly perfused organ (eg brain, lungs, liver & heart) will achieve equilibrium quickly after administration

Question 12

Factors affecting elimination of inhalation GA

Answer 12

1. conc of anaesthetic in inhaled air
2. perfusion of lungs
3. solubility of anaesthetic in blood

• increase means increase elimination
• most inhaled GA are eliminated through expired breath

Question 13

Halothane

Answer 13

• first modern inhaled anaesthetic
• potent (MAC 0.75%)
• medium rate of onset & recovery
• little or no analgesic until unconsciousness supervenes
• relaxes muscles & potentiates skeletal muscle relaxants

Question 14

Halothane ADR (3)

Answer 14

1. respiratory depression (dose dependent)
2. bradycardia & arrhythmias (hypotension & dysrhythmia)
3. halothane-associated hepatitis

Question 15

Isoflurane

Answer 15

• pungent smell
• potent (MAC 1.4%)
• medium rate of onset & recovery

Question 16

Isoflurane ADR (2)

Answer 16

1. bradycardia & arrhythmias
   - similar to halothane but reduced hypotension & arrhythmias
   - hypotension due decrease systemic vascular resistance
2. metabolism of isoflurane produce inorganic F (nephrotoxic)

Question 17

Sevoflurane

Answer 17

• potent (MAC 2%)
• more rapid rate of onset & recovery than halothane
• metabolised by liver

Question 18

Sevoflurane ADR (2)

Answer 18

1. metabolism of sevoflurane produce inorganic F (nephrotoxic)
2. usage of CO2 absorbent in vaporiser produce nephrotoxic agent

Question 19

Nitrous oxide

Answer 19

• aka dinitrogen oxide
• rapid onset & recovery but lack potency (MAC 110%)
• analgesia & amnesia but no complete consciousness/surgical anaesthesia
• only can used to supplement analgesic effect for primary anaesthetic
• used alone for analgesic effect (eg dentist & labour)

Question 20

Nitrous oxide ADR

Answer 20

post-operative N/V

propofol have less post-operative N/V

Question 21

IV GA (3)

Answer 21

1. Thiopentone
2. Propofol
3. Ketamine

Question 22

Advantages of using a combination of inhaled + IV (2)

Answer 22

1. reduce dose of inhaled GA

2. produce additional effects that cannot be achieved with an inhalation alone

Question 23

Thiopentone / thiopental

Answer 23

• high lipid solubility
• MOA : enhance GABA binding to GABA receptors
• rapid onset & recovery (high lipid solubility)
• extensive plasma protein binding (mainly hepatic elimination)
• duration of action depends on :
  1. elimination rate
  2. hepatic function (cirrhosis)
  3. Vd
  4. active metabolite (pentobarbital)

Question 24

Propofol

Answer 24

• rapid onset & faster recovery
• used for both induction & maintenance (continuous infusion of low dose)
• used for day surgery

Question 25

Propofol ADR

Answer 25

1. N/V (but lesser than nitrous oxide, anti-emetic) 2. Cardiovascular effect (bradycardia & hypotension) - to be used in caution in elderly, compromised cardiac function & hypovolemic

Question 26

Ketamine

Answer 26

- racemic but S- > R+ - produce dissociative anaesthesia - produce sedation, amnesia, analgesia & immobility - rapid induction and recovery - used for both induction & maintenance (continuous infusion of low dose) - hepatic metabolism to less active metabolite

Question 27

Ketamine ADR

Answer 27

1. psychological reactions (hallucination, delirium) - treat with premedication of diazepam & midazolam - dissociative anaesthesia

Question 28

Blood solubility and onset of action

Answer 28

Increase blood solubility, longer time taken for onset of action Affect onset only, not efficacy

Question 29

Halothane vs Isoflurane in BP reduction

Answer 29

Halothane - due to depression of cardiac output Isoflurane - due to decrease in systemic vascular resistance

Question 30

Advantages of Ketamine (4)

Answer 30

1. Analgesia 2. Sedation 3. Amnesia 4. Immobility

Question 31

GA with analgesia

Answer 31

1. Ketamine | 2. Nitrous oxide

Question 32

Opioid agonist used together GA

Answer 32

Remifentanil - 10min duration - 300x more potent than morphine