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Mechanical Ventilation- Trigger, Limit and Cycle

So how can you work out what are the phase variables in the ventilator cycle? Go back to this page to understand the cycle variables again if you are not sure.

Trigger Variable

Does the inspiration start because a preset pressure is detected? -YES- Inspiration is pressure triggered

NO

Does the inspiration start because a preset flow is detected?- YES- Inspiration is flow triggered

NO

Does the inspiration start because a preset volume is detected?- YES- Inspiration is flow triggered

NO

Inspiration starts because a preset time interval has elapsed?- YES- Inspiration is time triggered

Limit Variable

Does peak pressure reach preset value before inspiration ends?- YES- Inspiration is pressure limited

NO

Does peak volume reach preset value before inspiration ends?- YES- Inspiration is volume limited

NO

Does peak flow reach preset value before inspiration ends?- YES- Inspiration is flow limited

Cycle Variable

Does inspiratory flow end because a preset pressure is attained?- YES- Inspiration is pressure cycled.

NO

Does inspiratory flow end because a preset pressure is attained?- YES- Inspiration is volume cycled.

NO

Does inspiratory flow end because a preset flow is attained?- YES- Inspiration is flow cycled.

NO

Inspiration ends because a preset time interval has elapsed.- YES- Inspiration is time cycled.


Chatburn RL. Classification of Mechanical Ventilators. Respir Care 1992

Guidelines for the management of tracheal intubation in critically ill adults

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