Neuromuscular blocking agents Flashcards
What anaesthetic agents carry out partial neuromuscular blocks?
ACP Alpha 2 agonists Hypnotics (propofol) Volatiles (isoflurane) Guiaphenesin (equine)
When is a neuromuscular block agent requIred?
Ocular surgery Thoracic surgery/abdominal surgery mechanical ventilation Certain orthopaedic joint repositioning surgeries Endotracheal intubation Mydrais in birds
What is the mechanism of the neuromuscular junction?
Neuromuscular junction
Post synaptic ach receptors
2 Alfa, 1 beta, 1 delta and 1 gamma subunits
Two ach need to bind to the alpha subunits before signal is transmitted
Clearance of the synaptic cleft is carried out via acetylcholine-esterase
How do the two types of neuromuscular blocking agents carry out their effect on the neuromuscular junction?
Depolarised suxamethonium
Activate the receptor and keeps it in an activated state making it insensitive to ach
Non depolarised
Atracurium and vencruroium
Competes with the ach receptor (competitive block)
What are the consequences of a full neuromuscular block?
No breathing reflex Physical signs of anaesthesia are gone Jaw tone Eye position Palpebral reflex Respiratory rate Gross movement
How should the depth of anaesthesia be monitored in a neuromuscular blocked patient?
Sympathetic responses Tachycardia Hypertension Tear production Dilated pupils Salivation
What is required when a patient is blocked via a neuromuscular agent?
Ventilation
Sufficiently deep anaesthesia
Adequate analgesia
Name two types of depolarising neuromuscular agents
Atracurium
Vecuronium
Discuss the characteristics of atracurium
Competitive Binds to ach receptor but a inactive
Only one site of the receptor needs to be bound
Intermediate acting 30-40 minutes
Degraded by Hoffman degradation and non specific plasma choline esterases
Ideal for renal/hepatic patient
Minimal to non cardiovascular response
May cause histamine release
Discuss the characteristics of vercuronium
Competitive non depolarising
Short acting 20 minutes
Excreted unchanged by bike unsuitable for hepatic patient
No cardiovascular side effects
Discuss the characteristics of Suxamethonium
Depolarising non competitive
2 ach molecules joined together mimics natural ach leads to depolarisation and therefore contraction before relaxation
Not degraded by ach-esterases but by plasmacholinesterase
Cardiovascular response Tachycardia or bradycardia and hypertension
Increased ocular pressure
Increased intrgastric pressure
Increased intercranial pressure
Malignant hyperthermia
Non reversible
How can respiration be used to monitor a NMB?
Look at effort
Very unreliable as respiratorymuscles very resistant to neuromuscular blocking agents
Upper airway muscles may still be dysfunctional so monitor after extubation
How’s may you assess the neuromuscular block?
Peripheral motor nerve stimulation Stimulate peripheral nerve with clear motor response output Avoid stimulating the muscle Ulna Perneoal Facial Either get a single twitch Or look at TOF
What is TOF in NMB?
Train of four
Stimulate the nerve in blocks of 4 get 4 twitches
When blocked you may only get the 1st twitch
Loss of T4 75% of receptors blocked
Loss of T3 80% blocked
Loss of T2 90% blocked
Loss of T1 100% blocked
It is safe to recover the patient when T4 is back to 90% meaning less than 75% is blocked
Visual or tactile assessment is only possible when T4/T1 is less than 40% always use acceleromyography
Only possible for non-depolarising block
Why is it important to monitor patients closely during recovery?
As distal limb muscles will be affected differently compared to other muscle groups such as the upper airway muscles
Even if the T4 is back in the limb the upper airway muscles may still be blocked
