Module 4b: specific neuromuscular blocking agents Flashcards
What is the chemical structure, ampoules and dosage of suxamethonium?
Struc: 2Ach molecules
Amp: 100mg (2mls)
Dose: 1-2mg/kg
What are the effects of suxamethonium?
Profound paralysis in 60 sec
Ultra-short acting
Causes fasiculations
Lasts 5 min
How is suxamethonium excreted?
metabolised by pseudocholinesterase(synthesised in liver and found in plasma)
In what state is suxamethonium markedly decreased
Scoline apnoea:
- homozygous/heterozygous
- Prolonged paralysis
- Supportive treatmenr with ventilation + sedation
What are side effects of suxamethonium?
myalgia
bradycardia
hyperkalaemia and arrythmias
triggers MH
scoline apnoea
histamine release
What are the contraindications for suxamethonium
drug allergy
scoline apnoea
MH
unkown myopathies
Risks of hyperkalaemia (renal failure, paralysis, crash/burn injury)
What are the 2 types of non depolarizing agents?
Benzylisoquinolines: atracurium/cisatracurium
Aminosteroids: pancuronium, vecuronium and rocuronium
What is the dosage in non-depolarising agents based on?
lean body mass
What is the pharmacology of non-depolarisers?
marked paralysis in 1-5min
no fasciculations
short acting, intermediate acting, long acting
Metabolism: hepatic, hoffman degradation
Excretion: renal, hepatobilliary
Give the characteristics of vecuronium?
powder mixed with water
cardiovascularly stable
no histamine release
intermediate acting
largely hepatobiliary excretion-> safe in renal failure
Give the characteristics of Rocuronium?
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
What are the characteristics of atracurium?
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
Give the characteristics of cisatracurium
No histamine release
Safe in renal failure
Intermediate acting
Slower onset of action
How do you reverse non-depolarising agents
Should be reveresed when safe to do so
Reversal does not mean waking patient up
USUSUALLY USE AchE
What drugs are used for reversal?
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)
What are the typical adult reversal dosages?
neostigmine 2.5mg + glycopyrrolate 0.4-0.6mg
neostigmine 2.5mg + atropine 1mg
True or false: reversal should be given with suxamethonium
False, reversal agent will prolong effect of suxamethonium
When is it safe to reverse?
Use peripheral nerve stimulator with at least 3 twitches. If patient is breathing adequately=generally safe to administer muscle relaxant
What percentage of NMJs will still be blocked even if you get 4 twitches on peripheral nerve stimulator
75%
Why is it important to give reversal in liver and renal impaired patients?
Muscle relaxant cannot be metabolized and excreted properly so needs reversal
What are the signs of inadequate reversal
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
How do you manage inadequate reversal?
- Exclude other cause: anaesthetic agents, analgesia, hypo/hypercarbia
- Maintain ventilation
- Reverse any potentiators(warm patient, Mg, K, Ca)
- Use PNS
- Repeat dose of neostigmine (max 5mg)
What is sugammadex
used to reverse rocuronium
SRBA( selective relaxant binding agent)
