Flat Line on Medical Monitors: Asystole on ECG, EEG Brain Death, Pulse Oximetry Signal Loss

Definition

A flat line on a medical monitor/tracing indicates absence or cessation of a biological signal.

Common Contexts

1. ECG/EKG – Flat line = asystole (no cardiac electrical activity), definitive sign of cardiac arrest; requires immediate resuscitation.
2. EEG – Flat line = no brain electrical activity; associated with deep coma or brain death.
3. Pulse Oximetry – Flat line = lost pulse or poor signal; cannot measure oxygen saturation.

Clinical Note

Interpretation must always correlate with other clinical findings and be guided by healthcare professionals. Implications vary by context and patient condition.