Muscle Relaxants

Question 1

How do they work

Answer 1

Interrupt normal transmission of impulse from motor nerve to muscle synapse
Act at NMJ to block release to acetylcholine by occupying receptors

Question 2

Administration, speed on onset & duration of action

Answer 2

Slow IV
Most take effect in mins
Lasts ~10-30mins depending on agent

Question 3

Depolarising agents

Answer 3

Cause single surge of activity followed by no response to stimulation at muscle end plate
Short duration
Cannot be reversed

Question 4

Depolarising agent example - speed on onset & use

Answer 4

Suxamethonium
Rapid onset
Feline intubation

Question 5

Non-depolarising agents

Answer 5

Do not cause initial surge of activity at NMJ
Variable duration
Can be reversed

Question 6

Examples of non-depolarising agents

Answer 6

Altracurium

Vercuronium

Question 7

Effect on patient & order of muscle relaxation

Answer 7

Affects skeletal muscle only inc. resp. Muscles

1. Facial & neck muscles
2. Tail, limb & abdo muscles
3. Intercostal & diaphragmatic muscles

Question 8

Reversal - how it works & agent examples

Answer 8

Non-depolarising only
Anti-cholinesterase agents
Prevent breakdown of ace; increases neurotransmitter levels
Edrophonium / neostigmine

Question 9

Reversal - adverse effects & prevention

Answer 9

Bradycardia
Increased bronchial & salivary secretions
Prevention w/prior admin of an anti-cholinergic

Question 10

Disadvantages of muscle relaxants

Answer 10

IPPV req.
Difficult to assess anaesthetic depth
Some agents cause hypotension
Hypothermia common side effect due to decreased muscle tone

Question 11

Indications for use

Answer 11

Thoracic sx / diaphragmatic repair
Ortho sx
Ocular sx
Intubation in cases of laryngospasm