Pulmochart Reference
Definition and calculation of respiratory pressure parameters

Respiratory pressure parameters


The SPIRO app considers the peak inspiratory pressure (PIP), the positive end-expiratory pressure (PEEP), the mean airway pressure (Pmean) and the dynamic compliance (Cdyn).


Peak inspiratory pressure (PIP (cmH20))
The peak inspiratory pressure is the maximum pressure during ventilation, see [Rimensberger2015] p.302. Depending on the ventilation mode the PIP can represent different respiratory system characteristics.

Note: The PIP value does not only depend on the pressure applied during ventilation. It is also influenced by spontaneous breathing of the patient.
For example in the case of CPAP ventilation (continuous positive airway pressure) without spontaneous breathing, the PIP corresponds to the applied pressure. But with spontaneous breathing the detected PIP value is a mixture of the applied ventilation pressure and the pressure resulting from breathing.

PIP is detected by the software as the maximum pressure between two inspiratory onsets.

Positive end-expiratory pressure (PEEP (cmH2O))
PEEP, sometimes also called P-low, is the elevation of the baseline pressure during ventilation, see [Tobin2013] p.49, 89 and [Lucking2012] p.273. The PEEP value is generally a setting of the applied ventilation mode, that maintains the patency of lungs. This is even more important in the ventilation of newborns, than in the ventilation of adults. For newborns there is a concept of physiologic PEEP to avoid airway closure and ventilation-perfusion inequalities.
In ventilated patients the baseline or expiratory pressure is set relative to the atmospheric pressure. Usually the baseline pressure exceeds the atmospheric pressure, resulting in a positive PEEP value.

In this software PEEP is defined as the pressure at the time point before the positive pressure inflation starts. The software detects the onset of the increase of the P signal with a cross detector with a manually adjustable hysteresis value (default PEEP detection value=1).
The PEEP value is the intersection point of the raw pressure signal and a delayed pressure signal shifted with the PEEP detection value during expiration.

By decreasing the PEEP detection value, the software becomes more sensitive. This is important in older versions, where PEEP is calculated between two inspiratory onsets, while now only the expiratory pressure between an expiratory- and an inspiratory onset are considered. Older version could also detect the onset of a pressure increase in the plateau of the inspiration. By increasing the PEEP detection value, the software becomes less sensitive, therefore it could detect the pressure increase delayed.

The applied PEEP detection algorithm is developed for pressure based ventilation modes and might be not precise enough for volume based ventilation modes, see ("Mechanical ventilation").

Mean airway pressure (Pmean (cmH2O))
Definition: The mean airway pressure is in general the average airway pressure over a given time interval, see [Rimensberger2015] p.303, 306. As usually the given time interval is set to one respiratory cycle.

Pmean is calculated as the average airway pressure (Pmask) between two inspiratory onsets.

Dynamic compliance (Cdyn (mL/cmH2O/kg))
Compliance describes the expansion due to a pressure change. The dynamic compliance is a resistive properties of the respiratory system, see [Rimensberger2015] p.312. It relies on the volume- and the pressure change between the end-inspiration and the end-expiration.

The dynamic compliance is calculated as