Interpretation of Ventilator Graphics. Dr.Ahmed Abd Elmaksoud, MD. What is ventilator waveform?. Parameters displayed in waveform:. Volume Pressure Flow Time Exhaled P co 2. Physics review. A pressure difference ( ∆ p) must be present to make a fluid to flow
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Dr.Ahmed Abd Elmaksoud, MD
A pressure difference (∆p) must be present to make a fluid to flow
The higher the pressure difference the higher the flow
Flow is measured as the volume of the fluid passed a certain point in unit time,
It is the pressure difference divided by the flow caused by it
The compliance of a system is the volume change per unit change in pressure
The Work of Breathing:
It is the pressure difference across the system multiplied by the volume of the fluid moved by it
Mode of ventilation
Ventilator properties and settings
Respiratory properties of the patient
Pressure – time
Volume – time
Flow – time
Pressure – volume
Volume – Flow
Flow – pressure
Volume–oriented breath (modes)
Pressure–oriented breath (modes)
Pressure – time curve shows airway pressure, breath timing, the breath type delivered and patient versus machine triggering
The level of pressure at “B” is affected by the resistance and the flow
The level of the plateau pressure is determined by the compliance and the tidal volume
Lung recruitment and leaks in the system are possible reasons for further slight decrease in pressure (points D to E).
In pressure-oriented ventilation, Pressure increases rapidly from the lower pressure level until it reaches the upper pressure value and then remains constant for the inspiration time set on the ventilator.
Constant flow is a typical feature of a classic volume – oriented mode of ventilation.
Decelerating flow is a typical feature of a pressure – oriented mode of ventilation.
Volume controlled ventilation
Pressure controlled ventilation
Pressure support ventilation
The area to the left of the vertical axis (A) is a measure of how much work the patient needs to do to trigger the ventilator. The area to the right of the axis (B) represents the work done by the ventilator to support the patient
As compliance decreases, and the ventilator settingsremain the same, the PV loop in volume-controlled ventilation takes an increasingly flat course.
The change in resistance during constant flow ventilation changes the position of the inspiratory branch of the loop while its steepness remains unchanged
A change in the height of the PV loop is a measure of the strength of the patient’s inspiratory effort (if the ventilator parameters are unchanged)
PV loops measured before and after resistances
The work of breathing can be much greater than what is displayed in PV loops if the pressure is measured before resistances
The reason for setting assisted spontaneous breathing is generally to try to compensate for these airway resistance
Changes in the shape of volume – flow loop are used to obtain information about airway resistance
Increased airway resistance due to increased secretions
Approximately 200ml of volume is lost
Approximately 75ml of volume is lost
The presence of positive pressure in the lung at the end of exhalation due to air trappingCauses:Insufficient expiratory timeIncreased expiratory resistanceEarly collapse of unstable airway