General Anaesthesia

Question 1

Define General Anaesthesia

Define balanced anaesthesia

Answer 1

General Anaesthesia: Reversible, drug induced unconsciousness to allow performing of surgical procedures

Balanced Anaesthesia: administration of a mixture of small amounts of several neuronal depressants (e.g. anaesthetic agents, benzodiazepines to cut back anaesthetic dosage, anti emetics, muscle relaxants) to sufficiently maximizes the desired effect, but keeping disadvantages of the individual components to a minimum

Question 2

IV general anaesthesia

Answer 2

1. Barbituates (allosterically binding to GABAa b3 receptor)
   
   • Propofol (most widely used);
   • Etomidate (painful injection but less side effects on CVS/BP)
2. Thiopentone (used when risk of aspiration)
3. Ketamine (NMDA glutamate receptor antogonist-used in army fields, RTA - cause dissociated consciousness)

Question 3

Inhalation anaesthesia

Answer 3

Induction of anaesthesia in children but mostly used to maintain induced unconsciousness

1. No/Entonox - NMDA glutamate receptor antagonist - used as analgesics in labour and trauma
2. Fluranes

• Isoflurane, Desflurane - irritant to airways;
• Sevoflurane - relatively well tolerated

Question 4

Outline pharmagokinetics in general ananesthesia

Answer 4

1. MAC (minimum alveolar concentration): concentration at which 50% of population will not move to surgical stimulation
   
   • Lower MAC — Higher Lipid solubility — More potent general anaesthetics (Overton Mayer Hypothesis)
2. More blood soluble, decrease in partial pressure, slower speed on onset
3. Redistribution to intermediate compartments other than CNS (e.g muscles) leading to awakening of patients

Question 5

Effect on CVS

Answer 5

1. -ve ionotropes — reduced contractility — reduced CO
2. Vasodilation — decrease in TPR — BP drops
3. (Apart from ketamine — increase in stroke volume, heart rate, hence CO and BP)

Question 6

Effect on Respiratory system

Answer 6

respiratory suppression

IV – reduced rate

Inhalational — reduced tidal volume

overall reduced minute volume — monitor CO₂

(Apart from ketamine — increased respiratory rate)