Why has the breath been given?
There can be a controlled breath or an assisted breath.
Controlled breath: The respiratory rate on the ventilator is set to 12 breaths per minute for example. So every 5 seconds it will trigger a new breath. The trigger is, therefore, time.
Assisted breath: This breath is initiated when the patients initiates a breath which then drops the airway pressure or causes a change in the gas flow in the circuit. The trigger is, therefore, the patient.
What is our goal when delivering the breath?
There can either be set flow or set pressure.
Set flow: The ventilator will aim to deliver 60 litres per minute for example, during the breath. Monitoring of the peak inspiratory pressure and plateau pressures becomes important here as they are the dependent variables.
Set pressure: The pressure could be set to 20 cm H2O for example. So the ventilator will not go above this pressure when delivering the breath. This makes the lung compliance important when thinking about how much gas the ventilator will be able to deliver.
Why has the breath stopped?
The set volume could have been achieved e.g. 500mls.
The set time (Ti) could have been reached e.g. 0.8secs.
A decrease in flow rate could have been detected - pressure support.