5 General Anaesthetics Drugs

Question 1

Stages of General Anaesthetics

Answer 1

1) Analgesia ( without amnesia/ loss of touch sensation, consciousness retained)
2) Excitation ( with delirium and struggling)
3) Surgical anaesthesia ( with a loss of consciousness, decreased eye movement and pharyngeal reflex, progressive decrease in thoracic breathing and general muscle)OPTIMAL
4) Medullary depression ( progressive loss of CV and respiratory reflexes, no eye movement)

Question 2

Steps of General Anaesthetics

Answer 2

1) Premedication:
Produce amnesia–> benzodiazepine
Preventing PONV–> anti emetics)

2) Induction of anaesthesia:
IV/ inhalation agents

3) Muscle relaxation and intubation:
Anticholinergic agents

4) Maintenance of anaesthesia:
Inhalational agents( Maintain stage 3 anaesthesia)

5) Analgesia:
High potency opioid

6) Reversal:

Question 3

General anaesthetics Overview

Answer 3

IV Anaesthetics: Thiopentone, Propofol, Midazolam, Ketamine, Fentanyl

Inhalation Anaesthetics:
N2O, Halothane, Isoflurane, Desflurane, Servoflurane

Question 4

Minimum Alveolar Concentration (MAC)

Answer 4

The concentration in the inspired air at which 50% of patients have no response to a skin incision ( higher lipid solubility/ higher potency–> lower MAC)

0. 3-0.5 MAC- block voluntary reflexes and control perceptive awareness
1. 7-2.0MAC- block autonomic reflexes to nociceptive stimuli

Question 5

Thiopentone

Answer 5

Type: barbiturates ( Targets GABA A receptor)

Ultra short acting

Has hypnotic action

Unsuitable for repeating dose because of delayed recovery

Side effects: hypotension, apnea, myocardial depression

Question 6

Propofol

Answer 6

Targets GABA A receptor

Ultra short acting

Has hypnotic action

Suitable for anaesthesia maintenance by repeated dosing.

Side effects: hypotension and apnea

Question 7

Midazolam

Answer 7

Type: benzodiazepine ( Targets GABA A receptor)

Slow acting

Has hypnotic action

Unsuitable for repeating dose because of delayed recovery

Side effects: pain on injection

Question 8

Ketamine

Answer 8

Targets NMDA receptor

Slow acting

After effects common during recovery

Hypnotic, induce amnesia and profound analgesic

Doesn’t significantly affect respiration

Side effects: hallucination, dysphoria, increased heart rate, hypotension, and apnea

Question 9

Fentanyl

Answer 9

Type: Opioid ( Targets Opioid receptor)

Question 10

Nitrous Oxide (N2O)

Answer 10

MAC(%): 105

Advantages: low solubility in blood ( rapid induction and recovery)

Disadvantages/ Side effects: Weak anaesthetic
Prolong exposure can inactivate methionine synthase, Contraindicated in head injury

Question 11

Halothane

Answer 11

MAC(%): 0.75

Disadvantages/ Side effects: Hepatotoxic ( –> less commonly used now)

Question 12

Isoflurane

Answer 12

MAC(%): 1.17

Advantages: low solubility–> faster induction, less expensive

Disadvantages/ Side effects: Pungent smell

Question 13

Desflurane

Answer 13

MAC(%): 6.6.

Advantages: Most rapid onset, ultrashort acting

Disadvantages/ Side effects: Less potent, Pungent smell

Question 14

Servoflurane

Answer 14

MAC(%): 1.8

Advantages: low solubility in blood, not pungent, less hepatotoxic than halothane, GA induction is feasible by sevoflurane alone