Drugs

Question 1

Premedication general anaesthetics

Answer 1

Medications are given before the patient is put under a general anaesthetic to relax them, reduce anxiety, reduce pain and make intubation easier. These may include:

• Benzodiazepines (e.g., midazolam) to relax the muscles and reduce anxiety (also causes amnesia)

• Opiates (e.g., fentanyl or alfentanyl) to 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 2

Rapid Sequence Induction/Intubation

Answer 2

Rapid Sequence Induction/Intubation

Rapid sequence induction/intubation (RSI) is used to gain control over the airway as quickly and safely as possible where a patient is intubated in an emergency scenario and detailed pre-planning is not possible.

• This is considerably more risky, as the patient has often not been fasted (risk of aspiration), and the anaesthetist has not had the chance to plan for individual factors and potential problems (e.g., a difficult airway).

It is also used in non-emergency situations where the airway needs to be secured quickly to avoid aspiration, such as in patients with gastro-oesophageal reflux or pregnancy.

The procedure is designed to ensure successful intubation with an endotracheal tube as soon as possible after induction (when the patient is unconscious) to protect the airway. The biggest concern during RSI is the aspiration of stomach contents into the lungs. The bed can be positioned so the patient is more upright to reduce the reflux of contents up the oesophagus. Cricoid pressure (pressing down on the cricoid cartilage in the neck) may be used to compress the oesophagus and prevent the stomach contents from refluxing into the pharynx (this is somewhat controversial and should only be done by someone trained and experienced).

Question 3

Triad of general anaesthesia

Answer 3

There is a triad of general anaesthesia:

1. Hypnosis
2. Muscle relaxation
3. Analgesia

Question 4

Hypnotic agents

Answer 4

Hypnosis

Hypnotic agents are used to make the patient unconscious. They can be either given intravenously or by inhalation.

Intravenous options for a general anaesthetic include:

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

Inhaled options for a general anaesthetic include:

• 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 5

Muscle relaxants during anaesthetic procedures

Answer 5

Muscle Relaxation
Muscle relaxants block the neuromuscular junction from working. Acetylcholine (the neurotransmitter) is released by the axon but is blocked from stimulating a response from the muscle. Muscle relaxants are given to relax and paralyse the muscles. This makes intubation and surgery easier.

There are two categories:

• Depolarising (e.g., suxamethonium)
• Non-depolarising (e.g., rocuronium and atracurium)

Question 6

Analgesic agents used in anaesthesia

Answer 6

Analgesia

Opiates are the most frequently used medication for analgesia (pain relief). Common agents used in anaesthetics are:

• Fentanyl
• Alfentanil
• Remifentanil
• Morphine

Question 7

Anti ametics used post anaesthetic

Answer 7

Antiemetics are often given at the end of the procedure by the anaesthetist to prevent post-operative nausea and vomiting.

Common options for prophylaxis given at the end of the operation are:

• Ondansetron (5HT3 receptor antagonist) – avoided in patients at risk of prolonged QT interval
• Dexamethasone (corticosteroid) – used with caution in diabetic or immunocompromised patients
• Cyclizine (histamine (H1) receptor antagonist) – caution with heart failure and elderly patients