GENERAL ANAESTHETIC AGENTS

Question 1

What is the Aim of GA?

Answer 1

=To depress CNS functions whilst maintaining the functions of other vital body organs

Question 2

What are the Requirements during and after GA?

Answer 2

=Unconsciousness
=Analgesia
=Muscle relaxation
=Maintenance of physiological stability
=Suppression of visceral reflexes
=Amnesia

Question 3

What is Balanced Anaesthesia?

Answer 3

=No one anaesthetic agent can achieve all the requirements of GA; therefore GA involves the use of combinations of different types of drugs

=The term “balanced anaesthesia” refers to a combination of drugs used to take advantage of individual drug properties while attempting to minimize their adverse effects

Question 4

List the processes involved in GA

Answer 4

①Pre-medication
❷Induction of anaesthesia
③Initiation and maintenance of muscle relaxation
④Maintenance of anaesthesia
⑤Analgesia

Question 5

List the Aims of pre-medication

Answer 5

*Reduce anxiety
*Reduce salivary and respiratory secretions
*Suppress autonomic reflexes
*Produce amnesia
*Provide adjuvants for the maintenance of GA

Question 6

List the Drugs used in pre-medication

Answer 6

*Anti-muscarinic drugs (atropine, hyoscine and glycopyronium)

*Benzodiazepines (diazepam, temazepam, lorazepam and midazolam)

Question 7

What are the Uses of benzodiazepines in Pre-medication?

Answer 7

Anxiolysis, sedation and amnesia, and as adjuvants to general anaesthetics

Question 8

What are the Uses of anti-muscarinic drugs in Pre-medication?

Answer 8

=To suppress bronchial and salivary secretions which are increased by intubation, upper airway surgery and some inhalation anaesthetics

=To prevent bradycardia and salivation caused by neostigmine
=To prevent bradycardia and hypotension associated with drugs such as halothane, propofol and suxamethonium

Question 9

Which drug(s) is used for muscle relaxation in general anaesthesia?

Answer 9

=Succinylcholine (suxamethonium)
*Acts rapidly within seconds and last for approximately 3-6 minutes
*Used during induction of anaesthesia to provide muscle relaxation of short duration (e.g. immediately after thiopental or before tracheal intubation)

**Adverse effects: Histamine release producing a rash, bradycardia, somatic pain resulting from fasciculation , hyperkalaemia, persistent neuromuscular blockade due to pseudocholinesterase deficiency (affects 1:7,000 of population), malignant hyperthermia, increased intra-ocular pressure and increased gastric pressure

Question 10

Which ones are the non-depolarizing muscle relaxants?

Answer 10

=Include tubocurarine, atracurium, vencuronium, gallamine and pancuronium

=MoA: Competitive antagonism of acetylcholine nicotinic receptors
Have durations of action ranging from 15 minutes to more than 1 hour

=Used for both initiation and maintenance muscle relaxation, and when mechanical ventilation is necessary
Reversed with neostigmine (an anti-cholinesterase)

Question 11

Describe the induction of anaesthesia

Answer 11

=Induction is the transformation of an awake patient into an anesthetized one
=Induction is usually done with intravenous drugs, which produce rapid effects with minimal unpleasant effects
=Can also be done with inhalational anaesthetics (e.g. sevoflurane)

Question 12

Describe the maintainance of anaesthesia

Answer 12

=At this point, the drugs used to initiate the anesthetic are beginning to wear off, and the patient must be kept anesthetized with a maintenance agent

=Maintenance is usually done with inhalational anaesthetics (can be done with intravenous anaesthetic for some surgical procedures e.g. ketamine, midazolam and propofol)

Question 13

Describe the MoA of general anaesthetics

Answer 13

=They interact with ligand-gated membrane ion channels
=They increase potassium efflux through potassium channels resulting in hyperpolarization (this inhibits neuronal activity)
=They increase activity of GABA-A receptors and reduce activation of excitatory receptors (glutamate and nicotinic)
**GA drugs affect all brain functions (motor, sensory, reflex activity, respiratory and autonomic regulation)

Question 14

Common Intravenous GA drugs:

Answer 14

=Thiopental, propofol, etomidate, ketamine and midazolam

Question 15

Common Inhalational anaesthetics:

Answer 15

=Nitrous oxide, halothane, sevoflurane, isoflurane, enflurane and desflurane

Question 16

Common Induction agents:

Answer 16

=IV drugs; halothane and sevoflurane

Question 17

Maintenance agents:

Answer 17

=Inhalational agents; ketamine (IM and IV bolus doses), midazolam and propofol (given as slow IV infusion)

**Ketamine and nitrous oxide are also used in special anaesthetic techniques that do not involve loss of consciousness (dissociative anaesthesia and neuroletanaesthesia respectively)