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A Comprehensive Educational Website (established 1998)

Designed, Produced, and maintained (Edition 12, 2022) by 

Bhavani Shankar Kodali MD

Updated September 2022

o clipart 2

A Flat Line


This may happen under the following circumstances:

Monitor has been just turned on and it is warming up.

Monitor periodically zeroes itself. Most units display 'zeroing' during this process.

Esophageal intubation

Accidental extubation


Circuit disconnection

Cardiac arrest

Sampling tube disconnection.