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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

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interpretation of ventilator graphics

Interpretation of Ventilator Graphics

Dr.Ahmed Abd Elmaksoud, MD

parameters displayed in waveform

Parameters displayed in waveform:





Exhaled Pco2

physics review

Physics review

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,

physics review5

Physics review

The Resistance:

It is the pressure difference divided by the flow caused by it

physics review6

Physics review

The Compliance:

The compliance of a system is the volume change per unit change in pressure

physics review7

Physics review

The Work of Breathing:

It is the pressure difference across the system multiplied by the volume of the fluid moved by it

ventilator waveforms depend on

Ventilator Waveforms Depend on:

Mode of ventilation

Ventilator properties and settings

Respiratory properties of the patient

types of ventilator waveforms

Types of Ventilator Waveforms


Pressure – time

Volume – time

Flow – time


Pressure – volume

Volume – Flow

Flow – pressure


pressure time curve

Pressure – time curve

Volume–oriented breath (modes)

Pressure–oriented breath (modes)

pressure time curve11

Pressure – time curve

Pressure – time curve shows airway pressure, breath timing, the breath type delivered and patient versus machine triggering

pressure time curve volume oriented mode15

Pressure – time curve (volume – oriented mode)

The level of pressure at “B” is affected by the resistance and the flow

pressure time curve volume oriented mode16

Pressure – time curve (volume – oriented mode)

The level of the plateau pressure is determined by the compliance and the tidal volume

pressure time curve volume oriented mode17

Pressure – time curve (volume – oriented mode)

Lung recruitment and leaks in the system are possible reasons for further slight decrease in pressure (points D to E).

pressure time curve pressure oriented mode

Pressure – time curve (pressure – oriented mode)

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.

flow time curve24

Flow – time curve

  • The course of the flow curve during inspiration is strongly influenced by the ventilation mode set on the ventilator
  • The course of the flow curve during expiration is influenced by the overall resistance and compliance of the lung and the system.
volume time curve

Volume – time curve

  • The transferred volume is calculated as the area underneath the flow curve
  • The maximum volume value is the transferred tidal volume (not the entire volume in the lung)
pressure volume loop

Pressure – volume loop

Volume controlled ventilation

pressure volume loop28

Pressure – volume loop

Pressure controlled ventilation

pressure volume loop29

Pressure – volume loop

Pressure support ventilation

pressure volume loop30

Pressure – volume loop

Spontaneous ventilation

pressure volume loop31

Pressure – volume loop

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

pressure volume loop32

Pressure – volume loop

As compliance decreases, and the ventilator settingsremain the same, the PV loop in volume-controlled ventilation takes an increasingly flat course.

pressure volume loop33

Pressure – volume loop

The change in resistance during constant flow ventilation changes the position of the inspiratory branch of the loop while its steepness remains unchanged

pressure volume loop34

Pressure – volume loop

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)

pressure volume loop37

Pressure – volume loop

PV loops measured before and after resistances

pressure volume loop38

Pressure – volume loop

The work of breathing can be much greater than what is displayed in PV loops if the pressure is measured before resistances

pressure volume loop40

Pressure – volume loop

The reason for setting assisted spontaneous breathing is generally to try to compensate for these airway resistance

volume flow loop

Volume – flow loop

Changes in the shape of volume – flow loop are used to obtain information about airway resistance

volume flow loop42

Volume – flow loop

Increased airway resistance due to increased secretions



  • Graphic trend displays enable ventilation processes to be assessed at a later stage.
  • An event which occurs suddenly calls for as much details as possible to be shown in the diagram; while assessing the process of weaning, for example, needs several days or even weeks to be displayed in one diagram.
air leak

Air leak

Approximately 200ml of volume is lost

air leak52

Air leak

Approximately 75ml of volume is lost

auto peep57

Auto - PEEP

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