L06 Neuromuscular blocking agent
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What is 'Balanced Anesthesia'?
- Hypnosis (unconsciousness)
- Analgesia (pain relief)
- Paralysis (relaxation)
Why do we need NMB?
- no movement for delicate microscopic surgery
- decrease muscle tone for easier retraction of body wall allowing room for surgery
When NMB is used, what else should be provided for the patient?
intra-tracheal intubation for mechanical ventilation as respiratory muscle is also paralysed
Give one example of Depolarising NMB.
Pharmacokinetics of Succinylcholine
e.g. Onset time, Offset time, Metabolism
- Onest time: 60 seconds (very rapid)
- Offset time: 10-15 mins (rapid)
- Metabolism: butyrylcholinesterase (plasma cholinesterase, pseudocholinesterase)
What should be expected if the patient receiving succinylcholine does not retain motion power after 10-15 mins?
Atypical pseudocholinesterase (very rare genetic trait)
Name 4 adverse effects of succinylcholine.
- Sinus Bradycardia
- Hyperkalemia (binding to extra-junctional receptors in muscle -> transient K+ release -> possible death)
- Phase II neuromuscular block
Why there are severe adverse effects of succinylcholine?
Succinylcholine binds to ACh receptors in teh ANS -> affecting both the sympathetic and asympathetic nervous output
Name 5 non-depolarizing NMBs.
- Mivacurium (Short-acting)
- Atracurium (Intermediate-acting)
- Cis- Atracurium (Intermediate-acting)
- Rocuronium (Intermediate-acting)
- Pancuronium (Long-acting)
Pharmacokinetics of Mivacurium
e.g. duration of action, onset, metabolism
- Duration of Action: 5-10 mins (short-acting)
- Onset: not rapid
- Metabolism: esterase (which is abundant in body leading to rapid elimination and short duration of action)
Pharmacokinetics of Atracurium
e.g. duration of action, metabolism
- Duration of Action: 20-30 mins (intermediate-acting)
- Metabolism: Hofmann elimination (not enzymatic but depends on temperature and pH -> good for storage as in low temp and low pH there will be no metabolism) -> high confidence in retaining the motion power regardless of the liver function of the patient
- most popular NMB
Why long-acting NMB is not preferred?
Giving Short-eacitng drugs continuously gives higher degree of flexibility
2 Mechanisms for terminating NMB effect
- Metabolism and elimination of NMB
- Acetylcholinesterase inhibition (anticholinesterase)
2 Types of drugs for terminating NMB actions
- chelating agent (suck out the drugs physically -> still under research)
Examples and Mechanism of Anticholinesterase
- Examples: Neostigmine and pyridostigmine
- Mechanism: decrease action of cholinesterase -> increase concentration of acetylcholine -> reverse competitive inhibition
Why there is a high incidence of pre-operative anaphylaxis of NMB?
- all NMB are quaternary ammonium compounds
- nowadays most cosmetics include quaternary ammonium compounds -> exposure again -> anaphylaxis
Which muscle is used for neuromuscular monitoring?
Adductor Pollicis Muscle
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