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Correct electrode placement is essential in order to stimulate the target motor nerve while avoiding a direct stimulation of the target muscle.
If the muscle is stimulated directly the effect of the NMBA (Neuromuscular Blocking Agent) in the neuromuscular junction cannot be assessed and contractions will occur even during a deep or profound block.
It is important that the cathode rather than the anode is placed on the most superficial nerve site in order to cause depolarization as opposed to hyperpolarization of the nerve.
Depolarization of the nerve requires less current than hyperpolarization and therefore producing a supramaximal current is far easier to achieve as opposed to if the polarities were reversed.
It is important to verify that the current setting is more or less the same as the current delivered. If the current delivered is much less than the current setting, there is a problem with the electrode skin interface. Possible causes can include a need for skin preparation or a defective electrode.
Possible Impedance Factors: