Neuromuscular blockade How does it work?
Neuromuscular blocking agents act at the neuromuscular junction. By preventing transmission from the motor nerve to the motor end plate they paralyze all striated muscle. The degree of blockade can be monitored by stimulating a motor nerve and measuring the resultant muscular contraction.
Nerve stimulators are simple electronic devices that produce a brief, variable amplitude electrical spike. The two electrodes are placed over a superficial motor nerve and when the machine produces a spike the motor nerve depolarizes. If no neuromuscular blocking agent has been given the muscles innervated by that nerve contract with a twitch. if the animal is fully paralyzed there will be no twitch, and as the drug wears off the twitch force will gradually increase to normal levels. The amplitude of the twitch can be assessed visually, or more objectively by measuring the force of contraction or the EMG produced by the contracting muscle. There is a great deal of literature on the interpretation of nerve stimulation because muscle relaxants are widely used in human anesthesia.
What does it tell us?
A nerve stimulator is an essential piece of equipment if you are using muscle relaxants in animals for recovery procedures. Before the animal wakes up from the anesthetic it is important to make sure that the effects of the muscle relaxant have worn off, and this is done using a nerve stimulator. The nerve stimulator can also be used to tell when supplementary doses of muscle relaxant are needed.
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