Sem 3, case 10 (general anaesthetic)

Question 1

What are the 2 drugs used in induction of general anaesthetic

Answer 1

Propofol
Isoflurane

Question 2

How is propofol administered?

Answer 2

IV injection

Question 3

What are the pros and cons to IV induction (propofol)?

Answer 3

Pros:
- rapid onset (3 secs)
- reduced number of complications
- misses excitatory phase
Cons:
- might not be easy to find the vein on some patients

Question 4

What are the pros and cons of inhalation induction (isoflurane)?

Answer 4

Pros:
- easier in difficult to obtain IV patients
- easier to use in paediatrics
- easier patients with airway difficulty
Cons:
- slower onset (7 mins)

Question 5

Which neurotransmitter do induction agents interact most with?

Answer 5

GABA
(via GABA-A receptor)

Question 6

What is the MOA of propofol?

Answer 6

Positive modulation of GABA inhibition via GABA-A receptor

= Increase GABA interaction with the GABA-A receptor = more inhibition of action potentials

Question 7

What is the MOA of isoflurane?

Answer 7

Binds to receptors:
- GABA
- NMDA
- Glycine

(Full MOA unknown)

Question 8

What are the side effects of propofol ?

Answer 8

Hypotension
Respiratory depression
Brady cardia
Nausea + vomiting
Adrenocortical suppression

Question 9

What are the side effects of isoflurane?

Answer 9

Hypotension
Respiratory depression
vasodilation (coronary)

Question 10

What are the main aspects of maintenance?

Answer 10

Maintaining:
- unconsciousness
- analgesia
- muscle relaxation
- airways

Question 11

How is unconsciousness maintained during general anaesthesia?

Answer 11

Continue administering the drug used in induction (propofol or isoflurane)

Question 12

How are airways maintained during general anaesthesia?

Answer 12

Usually:
- endotracheal tube (ET) = tube inserted past vocal cords
- tracheostomy tube = tube inserted at level of 2nd tracheal ring, passes vocal cords
- supraglottic airway (SGA) = tube inserted that sits on/in vocal cords

ventilate with O2 and Nitrous Oxide (NO)

Question 13

How is muscle relaxation maintained during general anaesthesia?

Answer 13

Using Ach antagonists
- atracurium
- suxamethonium

Question 14

How is atracurium administered?

Answer 14

IV injection

Question 15

How is suxamethonium administered?

Answer 15

IV injection

Question 16

What is the MOA of atracurium?

Answer 16

Ach antagonist at the motor end plate (NMJ) = competitive inhibitor

= NON-DEPOLARISING agent

Question 17

What is the MOA of suxamethonium?

Answer 17

Ach agonist (acetylcholinesterase resistant)
- mimics Ach but takes way longer to hydrolyse
- stays in NMJ receptors for longer, prolonging depolarisation
= neuromuscular blockade

= DEPOLARISING agent

Question 18

How does atracurium leave circulation?

Answer 18

Spontaneously hydrolyses in plasma

Question 19

How does suxamethonium leave circulation?

Answer 19

Hydrolysed by acetylcholinesterase rapidly after withdrawal

Question 20

What are the side effects of atracurium?

Answer 20

Hypotension
Bronchospasm
Ganglion block

Question 21

What are the side effects of suxamethonium?

Answer 21

Bradycardia
Hyperkalaemia
Increased intraocular pressure
Postoperative pain

(Same as glycopyrrolate)

Question 22

How is analgesia maintained during general anaesthesia?

Answer 22

Fentanyl = Opioid analgesic

Question 23

How quickly do induction agents ware off if not replenished?

Answer 23

After 5-10 minutes

Question 24

How is unconsciousness reversed in the process of general anaesthesia?

Answer 24

Stop giving the induction agents (propofol or isoflurane)

Question 25

How is muscle relaxation reversed in the process of general anaesthesia?

Answer 25

Administer neostigmine and glycopyrrolate

Question 26

How is neostigmine administered?

Answer 26

IV injection (Or intramuscular injection/subcutaneous injection)

Question 27

How is glycopyrrolate administered?

Answer 27

IV injection (Or intramuscular injection/orally/topically)

Question 28

What is the MOA of neostigmine?

Answer 28

Reverses non-depolarising muscle relaxants (e.g atracurium) - blocks acetylcholinesterase = increases Ach in NMJ = increases muscle contraction

Question 29

Which drug must be administered alongside neostigmine?

Answer 29

Glycopyrrolate

Question 30

Why does glycopyrrolate need to accompany neostigmine?

Answer 30

Limits the parasympathomimetic side effects of neostigmine (Parasympathomimetic drug = activates parasymp NS by mimicking/modifying Ach action)

Question 31

What are the side effects of neostigmine?

Answer 31

Hypotension Bradycardia Bronchoconstriction Muscular fasiculations

Question 32

What is the MOA of glycopyrrolate?

Answer 32

Muscarinic receptor ANTagonist = inhibits Ach transmission

Question 33

Which drugs in general anaesthesia can cross the BBB?

Answer 33

Induction agents (propofol, isoflurane) Atracurium metabolites (muscle relaxant) Atropine (a less potent alternative to glycopyrrolate, as that cannot cross BBB)

Question 34

What are the side effects of glycopyrrolate?

Answer 34

Bradycardia Hyperkalaemia Increased intraocular pressure Postoperative pain (Same as suxamethonium)

Question 35

What are the 2 main drugs used in induction?

Answer 35

Propofol (IV) Isoflurane (inhalation)

Question 36

What are the 2 main drugs used as muscle relaxants?

Answer 36

Atracurium Suxamethonium

Question 37

What are the 2 main drugs used in reversal of general anaesthesia?

Answer 37

Neostigmine Glycopyrrolate

Question 38

What are the most common drugs used as for analgesia in general anaesthesia?

Answer 38

Opioids - fentanyl - morphine - hydromorphone

Question 39

What are some of the premeds used before general anaesthesia? What do they do?

Answer 39

- benzodiazepines (sedation and amnesia) - opioids (analgesia and sedation) - anticholinergics (antiemetic = stops vomiting) - antibiotics (infection prophylaxis)

Question 40

Which drug does not get reversed by simply stopping administration?

Answer 40

Atracurium (use neostigmine and glycopyrrolate)

Question 41

What is some info needed before commencing general anaesthesia?

Answer 41

- Age - consent - BMI - airway inspection for intubation - PMHx - administer pre-meds