Module 4b: specific neuromuscular blocking agents

Question 1

What is the chemical structure, ampoules and dosage of suxamethonium?

Answer 1

Struc: 2Ach molecules
Amp: 100mg (2mls)
Dose: 1-2mg/kg

Question 2

What are the effects of suxamethonium?

Answer 2

Profound paralysis in 60 sec
Ultra-short acting
Causes fasiculations
Lasts 5 min

Question 3

How is suxamethonium excreted?

Answer 3

metabolised by pseudocholinesterase(synthesised in liver and found in plasma)

Question 4

In what state is suxamethonium markedly decreased

Answer 4

Scoline apnoea:
- homozygous/heterozygous
- Prolonged paralysis
- Supportive treatmenr with ventilation + sedation

Question 5

What are side effects of suxamethonium?

Answer 5

myalgia
bradycardia
hyperkalaemia and arrythmias
triggers MH
scoline apnoea
histamine release

Question 6

What are the contraindications for suxamethonium

Answer 6

drug allergy
scoline apnoea
MH
unkown myopathies
Risks of hyperkalaemia (renal failure, paralysis, crash/burn injury)

Question 7

What are the 2 types of non depolarizing agents?

Answer 7

Benzylisoquinolines: atracurium/cisatracurium

Aminosteroids: pancuronium, vecuronium and rocuronium

Question 8

What is the dosage in non-depolarising agents based on?

Answer 8

lean body mass

Question 9

What is the pharmacology of non-depolarisers?

Answer 9

marked paralysis in 1-5min

no fasciculations

short acting, intermediate acting, long acting

Metabolism: hepatic, hoffman degradation

Excretion: renal, hepatobilliary

Question 10

Give the characteristics of vecuronium?

Answer 10

powder mixed with water
cardiovascularly stable
no histamine release
intermediate acting
largely hepatobiliary excretion-> safe in renal failure

Question 11

Give the characteristics of Rocuronium?

Answer 11

most commonly used non-depolarizer
Cardiovascularly stable
High dose: 1mg/kg can provide intubating conditions for 1 min
Intermediate duration of action
Higher dose=longer paralysis

Question 12

What are the characteristics of atracurium?

Answer 12

histamine releasing->risk of anaphylaxis

Hoffman degradation, dependent of pH and temp

Has toxic metabolite->laudanosine

Safe in liver + renal failure

Intermediate duration of action

Question 13

Give the characteristics of cisatracurium

Answer 13

No histamine release
Safe in renal failure
Intermediate acting
Slower onset of action

Question 14

How do you reverse non-depolarising agents

Answer 14

Should be reveresed when safe to do so

Reversal does not mean waking patient up

USUSUALLY USE AchE

Question 15

What drugs are used for reversal?

Answer 15

Neostigmine:
- AchE, increases Ach concentration in synaptic cleft
- Ach competes with NDMR
- Ach increased nicotinic and muscarinic receptors= side effects

Anticholinergic agent (atropine or glycopyrrolate)
- an anti-muscarinic agent
- Given to prevent muscarinic effects (the B’s):
– Bronchial secretions
–Bronchospasms
–Bradycardia
–Beristalsis (peristalsis)

Question 16

What are the typical adult reversal dosages?

Answer 16

neostigmine 2.5mg + glycopyrrolate 0.4-0.6mg

neostigmine 2.5mg + atropine 1mg

Question 17

True or false: reversal should be given with suxamethonium

Answer 17

False, reversal agent will prolong effect of suxamethonium

Question 18

When is it safe to reverse?

Answer 18

Use peripheral nerve stimulator with at least 3 twitches. If patient is breathing adequately=generally safe to administer muscle relaxant

Question 19

What percentage of NMJs will still be blocked even if you get 4 twitches on peripheral nerve stimulator

Answer 19

75%

Question 20

Why is it important to give reversal in liver and renal impaired patients?

Answer 20

Muscle relaxant cannot be metabolized and excreted properly so needs reversal

Question 21

What are the signs of inadequate reversal

Answer 21

Jerky respiration
✓ Reduced VT
✓ Tracheal tug
✓ Restlessness, may be worsened by hypoxia
✓ Inability to raise head from pillow
✓ Weak hand grip
✓ Poor ability to cough
✓ ptosis

Question 22

How do you manage inadequate reversal?

Answer 22

1. Exclude other cause: anaesthetic agents, analgesia, hypo/hypercarbia
2. Maintain ventilation
3. Reverse any potentiators(warm patient, Mg, K, Ca)
4. Use PNS
5. Repeat dose of neostigmine (max 5mg)

Question 23

What is sugammadex

Answer 23

used to reverse rocuronium
SRBA( selective relaxant binding agent)