Tetany describes a constant stimulus to the nerve at 50 Hz. At 60 mA it is very painful for an awake patient.

Before a neuromuscular blocker is given, and after it has been properly reversed, the muscle contraction has no fade.

Following a tetanic stimulus the response to a single twitch is greater than normal, a phenomenon known as 'post-tetanic facilitation'. The TOF is stronger and the TOF count may increase when a tetanic stimulus is applied during partial blockade.

Tetany is used in the following situations:

1. During profound block, when no response is seen to a TOF, the presence of post-tetanic facilitation, in particular the number of twitches elicited, helps you to estimate the time until return of the TOF response and hence the time before reversal of blockade is possible
2. To check that the block has been reversed adequately. In this situation no fade is seen