Updated 4 April 2020
This page summarises the importance of pressure measuring and monitoring even in the simplest ventilation scenarios. A pressure gauge attached to the manual facilitator’s sensing port, while better than nothing, provides only partial information and cannot be used for triggering alarms or detecting inspiration in a non-paralysed patient and providing Assist Control, which is explained on the Clinical page.
The pressure sensor, described in Electrical Hardware and Controls, is to be connected in a position so as to allow sensing of pressure in the patient’s airway, as shown in Plumbing. Because pressure transducers with the correct specifications to sense human respiration are in low supply, these sensors should not be single-use. To protect the pressure sensor, a small inline HEPA filter should be placed on the sensing line between the patient and the sensor to prevent viral migration and patient to patient infection.
The first three readings should be displayed to the clinician and the fourth is a condition that must be detected.
- PEEP – (positive end-expiratory pressure) – This is manually set by the PEEP valve
- Plateau Pressure – This varies as a function of airway resistance
- PIP (Peak Inspiratory Pressure) – This varies as a function of airway resistance
- Inhalation Detection – This dip in pressure, with relation to the resting PEEP pressure, indicates that a non-paralysed patient is attempting to breathe and should initiate a cycle.
Sanity Checks & Alarms
There should be checking each cycles for relations and consistencies among PEEP, Plateau, and PIP and when discrepancies an alarm condition should be triggered accordingly:
- In Volume Control ventilation, it is expected that PIP > Plateau.
- It is expected that Plateau > PEEP in order to have a positive driving pressure. (Driving pressure = Plateau – PEEP)
- PEEP should not fall below a predetermined value, to prevent alveolar collapse, and the displayed value should match the value set manually with the PEEP valve.
- Plateau should not exceed a predetermined value, nominally 30 cm H2O in ARDS.
- PIP should not exceed a predetermined value; 40cmH2O in general. This value should be set (hard coded) to below the cracking pressure of the pop-off valve.
- A leak or disconnect in the system will be detected as plateau pressure below a predetermined level, e.g. 5 cm H2O.
Assist Control is dependent on a well executed pressure detection system, namely the ability to also read negative deflection of pressure when pressure falls below PEEP or baseline during a “detection window period” towards the end of expiration phase. For more information see Assist Control under Controls.