A situation may occur where measured peak pressure (Ppeak) and plateau pressure (Pplateau) are the same, and the question arises as to whether this has to do with the patient or the ventilator.
Measured peak airway pressure and plateau pressure can be the same in states where there is no flow occurring at the end of inspiration.
Definition of airway pressures:
Peak airway pressure (Ppeak) is measured at the airway opening and is routinely displayed by mechanical ventilators. It represents the total pressure needed to push a volume of gas into the lung and is composed of pressures resulting from inspiratory flow resistance (resistive pressure), the elastic recoil of the lung and chest wall (elastic pressure), and the alveolar pressure present at the beginning of the breath
Plateau pressure (Pplateau) is the pressure value that is maintained constant during a portion of the inspiratory phase of the breath during no flow. No flow means there is no more resistive pressure to overcome, therefore plateau pressure equals alveolar pressure.
Principles of measuring plateau pressures:
- Inspiratory hold: Manual end-inspiratory hold performed by the user
- Rapid interruption method: Short, automated end-inspiratory occlusion maneuver by the ventilator
- Least squares fit method: Computed calculation of Pplateau
Monitoring parameter Pplateau in Hamilton Medical ventilators
|Parameter (unit)||Monitoring window||Definition|
|Pplateau (cmH2O)||Monitoring 1||Plateau or end-inspiratory pressure. The pressure measured at the end of inspiration when flow is or is close to zero.
- In volume modes when the set Pause is greater than zero.
Pplateau is a rough representation of alveolar pressure.
As shown by Mojoli in 2015 (1), the Pplateau monitoring parameter calculated using the LSF method gives a good estimation of the actual plateau pressure in situations where the flow at the end of inspiration is or is close to zero. Pplateau will only be shown in the monitoring parameters under such conditions. If the end-inspiratory flow is too high or the end-inspiratory pressure is unstable, the parameter will not be available.
However, it is also possible to measure Pplateau manually by performing an inspiratory hold maneuver.
To perform an inspiratory hold maneuver:
- Ensure the Paw waveform is displayed.
- Open the Hold window.
- Wait until the Paw waveform plot restarts from the left side.
- Wait for the next inspiration.
- Then select INSP hold.
- When the flow reaches zero, deactivate the hold maneuver by selecting Insp hold again. After the maneuver, the Hold window closes, and the freeze function is activated automatically.
- Measure Pplateau by examining points on the curve with the cursor.
Relevant devices*: HAMILTON-G5/S1 (sw v2.6x); HAMILTON-C3 (sw v2.0.x), HAMILTON-C6 (sw v1.0.x).
* Some features are options. Not all features and devices are available in all markets.
1 Mojoli et al. Automatic monitoring of plateau and driving pressure during pressure and volume controlled ventilation. Intensive Care Medicine Experimental 2015 3(Suppl 1):A998.