10 NEUROMUSCULAR AGENTS

Question 1

What are the uses of a neuromuscular blocking agent in surgery

Answer 1

Paralysis of patients
prevents damage to vocal chords
Allows for intraoperative control of ventilation
Decreases O2 consumption
Decreases risk of barotrauma
Prevents increase in raises in intracranial pressure

Question 2

Describe the concept of balanced anaesthesia

Answer 2

Sleep/ sedation
Muscle relaxation
Analgesia

Question 3

Describe the events in the presynaptic terminal post AP

Answer 3

Depolarisation of neuron causes opening of Ca2+ channels. Influx of Ca2+ causes vesicles containing ACh to fuse with cell membrane and the ACh exits the cell via exocytosis.

Question 4

Describe the events in the synaptic cleft

Answer 4

ACh binds to ACh receptors. Around 200 qunata containing around 5000 molecules of ACh is released into the NMJ this activates 500k AChR

Question 5

Describe reuptake of ACh

Answer 5

ACh esterase is secreted by muscle fibres and immediately recycles 50% of ACh into acetate and choline. Choline recycled into nerve cell.

Question 6

Where do NMB bind

Answer 6

To nicotinic ACh receptors in the muscle fibre end plate

Question 7

Describe nicotinic ACh receptors

Answer 7

They are the receptors found on skeletal muscle that receive acetylcholine released to signal for muscular contraction.
Also used in transmission of signal in the autonomic nervous system.
Pentamaric in structure 2 alpha, 1 beta, 1 sigma. 1 Ach binds to each alpha subunit.

Question 8

Name the one NMB that depolarises the cell and its mechanism of action

Answer 8

Succinylcholine
Agonist at ACh receptor
Causes shaking before paralysis.
Broken down by pseudocholine esterase
Fast onset and elimination
Some have absent enzyme for break down and succinylcholine apnoea occurs

Question 9

Side effects of succinylcholine

Answer 9

Anaphylaxis, fasiculations can cause muscle pain. Cardiac dysrhythmias. Increased K+ (careful in trauma cardiac injury/ burns). Hyperpyrexia, increased intracranial pressure, intragastirc pressure and intraoccqular pressure

Question 10

What is the benefit of succinylcholine

Answer 10

Quickest safest way to have rapid airway control for intubation in emergency conditions. Minimal time for aspiration in patients with full stomachs.

Question 11

How do most NMB work

Answer 11

Through non-depolarizing. Blocking the actions of Ach. Competitive antagonist (Competitively binds receptor site, does not provoke action).

Question 12

What percentage of receptor sites are occupied for the drug to work

Answer 12

70% for effect. 90% for complete effect.

Question 13

Name the ultra short acting NMB

Answer 13

Succinylcholine

Question 14

Name the short acting NMB

Answer 14

Mivacurium

Question 15

Name the intermediate acting NMB

Answer 15

Atracurium, vecurnium, rocuronium

Question 16

Name the long acting NMB

Answer 16

Pancurronium

Question 17

What are some benefits of rocuronium

Answer 17

Rapid onset of action, can be used in emergency intubation if succinylcholine contraindicated. Mainly eliminated in the liver, good for renal patients. Minimal cardiac effects

Question 18

What are some considerations for reversal of NMBA

Answer 18

Patients needs to have use of muscles (resp!) post surgery. Either titrate in surgery for perfect duration (hard as unpredictable variables), or give reversing agent.

Question 19

Describe a reversing agent

Answer 19

Neostigmine- inhibits AChesterase. Results in more Ach. Causes autonomic side effects- bradycardia, salivation, nausea. Given with atropine to counter autonomic side effects.

Question 20

How is muscle activity (effectiveness of NMB) monitored in theatre

Answer 20

Using a nerve stimulator on abductor policis longus. Measure muscle twitches.