day 4 - Basic physiological and pharmacological principles in anaesthesia

Question 1

Anaesthesia ‘classical triad’

Answer 1

Hypnotic agent- unconsciousness
- Gas or IV
Analgesia
Neuromuscular Paralysis

Induction, Maintenance, Emergence, Recovery

Question 2

pharmacokinetics vs pharmacodynamics

Answer 2

What the body does to the drug
Absorption, distribution, metabolism, elimination

vs

What the drug does to the body – ie it’s effects
CVS, RS, GI, NS, Other , Side effects

Question 3

Typical Anaesthesia

Answer 3

induction of anaesthesia can be IV (most common) or volatile.

Intravenous induction:
Short acting opiate - e.g. fentanyl
Hypnotic ‘anaesthetic’ - e.g. propofol

volatile induciton:
oxygen in air or N2O with sevoflurane

additional considerations:
Specific muscle paralysis may be needed
Definitive analgesia
Anti-emetic
Others

maintenance: volatile or IV again. usually volatile - e.g. sevoflurane

Question 4

propofol

Answer 4

Induction is most commonly achieved by the intravenous injection of propofol or thiopental. Unconsciousness occurs within seconds and is maintained by the administration of an inhalation anaesthetic.

Propofol (2,6-diisopropylphenol) induces anaesthesia within 30s and is smooth and pleasant. Recovery from propofol is rapid, without nausea or hangover and, for this reason, it has largely replaced thio- pental. Propofol is inactivated by redistribution and rapid metabolism, and in contrast to thiopental, recovery from continuous infusion is relatively fast.

Question 5

Neuromuscular blockers

Answer 5

used if intubation is required or a still patient is needed. it can be either a depolarising or non depolarising (competitive) relaxant.

Depolarising
Suxamethonium

Non-depolarising (competitive vs ACh)
Atracurium
Vecuronium
Rocuronium

causes obtunding/loss of the potency of the airway so need to maintain this (manoeuvres, adjuncts, supralottic devices, endotracheal intubation)

Question 6

Reversal of Paralysis

Answer 6

Neostigmine
Blocks cholinesterase
Stimulates nicotinic and muscarinic
Given with an anticholinergic

Sugammadex

Just have to wait for sux to wear off
Non-depolarisers can be ‘reversed’

Question 7

Antiemetics

Answer 7

General- Hydrate, anxiety, gastric decompress

Cyclizine anti-histamine
- S/E – tachycardia and other anti-cholinergic effects

Ondansatron 5-HT3 receptor antagonists
- S/E – constipation + long QT

Prochlorperazine (‘Stematil’) – DA and mACh receptor antagonist
- S/E – extrapyramidal

Dexamethasone glucocorticoid
- S/E – deranged glucose control

Question 8

Guedel

Answer 8

An oropharyngeal airway (also known as an oral airway, OPA or Guedel pattern airway) is a medical device called an airway adjunct used to maintain or open a patient’s airway. It does this by preventing the tongue from covering the epiglottis, which could prevent the person from breathing. When a person becomes unconscious, the muscles in their jaw relax and allow the tongue to obstruct the airway.

The correct size OPA is chosen by measuring from the corner of the person’s mouth to the angle of the jaw. The airway is then inserted into the person’s mouth upside down. Once contact is made with the back of the throat, the airway is rotated 180 degrees, allowing for easy insertion, and assuring that the tongue is secured. An alternative method for insertion, the method that is recommended for OPA use in children and infants, involves holding the tongue forward with a tongue depressor and inserting the airway right side up.[1]

The device is removed when the person regains swallow reflex and can protect their own airway, or it is substituted for an advanced airway. Simply remove by pulling on it without rotation.

Question 9

Airway devices- above vs blow cords

Answer 9

Above Vocal Cords
eg , gudel, LMA

Below Vocal Cords - Into trachea = intubation, paralysis

Question 10

Atelectasis

Answer 10

Atelectasis (from Greek: ἀτελής, “incomplete” + ἔκτασις, “extension”) is defined as the collapse or closure of the lung resulting in reduced or absent gas exchange. It may affect part or all of one lung.[1] It is a condition where the alveoli are deflated, as distinct from pulmonary consolidation.

It is a very common finding in chest x-rays and other radiological studies. It may be caused by normal exhalation or by several medical conditions. Although frequently described as a collapse of lung tissue, atelectasis is not synonymous with a pneumothorax, which is a more specific condition that features atelectasis.

Question 11

anaesthetic CVS support

Answer 11

‘Uppers’

Anticholinergics

• Atropine
• Glycopyrulate 200-600μg

The anti-cholinergics atropine and glycopyrulate are used to reduce vagaly mediated bradycardia, and to dry secretions. Unlike atropine, glycopyrulate does not cross the blood-brain barrier, and does not cause sedation.

Symatheto-mimetics

• alpha 1 agonists
  
  • Phenylepherine
  • Metaraminol 0.25-0.5 mg
• Ephedrine
• mixed alpha and beta adreno agonist

Question 12

how do endotracheal tubes stay in place

Answer 12

they have a cuff to inflate in the trachea.

Question 13

perioperative considerations

Answer 13

• pain relief
• body position
• warmth
• fluid balance.
• cardiovascular support (as anaesthesia tends to depress) e.g. fluids, alpha and beta agonists, antimuscarinics.
• antibiotics
• blood and blood products

Question 14

postoperative considerations

Answer 14

• PTs normal drugs
• analgesia
• DVT prophylaxis

Question 15

emergence considerations

Answer 15

• analgesia
• anti-emetics
• reverse neuromuscular paralysis
• remove maintenance agents once paralysis reversed.
• remove intubation etc