1. Mechanical Ventilation Graphical Assessment

2. Outline Ventilator scalars and loops Control variables Phase variables
Other settings
Breath types
Breath sequence
Modes of ventilations
Outline

3. Ventilator Scalars and loops
Mechanical Ventilation Graphical Assessment
Ventilator Scalars and loops

4. Peak PAW
Plateau PAW
PRAW
End Expiratory PAW
Inspiratory Flow Time
Peak Inspiratory Flow
Inspiratory Hold Time
Zero Flow at Plateau Phase
Peak Expiratory Flow
Inspiratory Time
Expiratory Time
Tidal Volume .
The four parameters commonly monitored during mechanical ventilatory support are pressure, flow, volume and time. Output waveforms are conveniently graphed in group of three. The horizontal of all three graphs is the same and represents the unit of time. The vertical axes are in unit of pressure, flow and volume. Pressure is usually measured in the ventilator circuit and is taken as a reflection of patient airway pressure (Paw). However, pressure can also be measured in the mid esophagus (Pes) where it is taken as a reflection of pleural pressure. Flow (V) and volume (V) are commonly measured in the ventilator circuit. These measurements can be displayed in a variety of ways but are most commonly plotted as pressure, flow and volume over time. (Figure 1) depicts a typical pressure/flow/volume display over time during a ventilator controlled breath.
End Inspiratory Esophageal Pressure
End Expiratory Esophageal Pressure

6. Peak Airway Pressure
Plateau Airway Pressure
Peak Inspiratory Flow VT
Tidal Volume (VT)
Another common way to graphically display these parameters is to plot volume over pressure and flow over volume, the horizontal axis in the volume/pressure loop represents the change of pressure and the vertical axis represents the change of volume during the inspiratory and expiratory phases of the respiratory cycle and together they quantify how much pressure change is needed for the volume change. On the other hand, the volume/flow loop would represent the change of flow on the horizontal axis and the change of volume on the vertical axis (Figure 2).
Peak Expiratory Flow
End Expiratory Pressure

7. Mechanical Ventilation Graphical Assessment
Control Variables

8. Lung Compliance Decreased
There are two fundamental methods to control the delivery of a breath. The clinician can choose to keep either volume or pressure constant from breath to breath. The control variables most commonly used to describe modes of ventilation are volume-controlled (VC) ventilation and pressure-controlled (PC) ventilation. Within these two categories are multiple ways to tailor specific modes. In volume-controlled ventilator, clinician sets flow magnitude and pattern; the pressures used to deliver the set tidal volume will vary as a function of the patient’s pulmonary resistance and compliance and the his or her efforts in order to deliver that flow (Figure 3).
Set Tidal Volume Maintained

9. Set Pressure Maintained
Lung Compliance Decreased
In pressure-controlled modes the tidal volume is not guaranteed. Each breath is delivered at a set pressure for duration of time calculated based on the respiratory rate and the ratio of inspiration to expiration. The tidal volume will vary with changes in the patient’s lung mechanics or his efforts (Figure 4).
Delivered VT Decreased

10. Mechanical Ventilation Graphical Assessment
Phase Variables

11. A B C Pressure Trigger Sensitivity Flow Trigger Sensitivity
During mechanical ventilatory support, there are four phases during each ventilatory cycle: a) the trigger phase (breath initiation), b) the flow delivery phase, c) the cycle phase (breath termination), and e) the expiratory phase. Mechanically delivered breaths can be described by what determines the trigger, flow delivery, and cycle parameters for that breath.
Triggers are of three types: machine timer, pressure change, and flow change. With a machine timed trigger, the clinician sets a rate and mechanical breaths are initiated by a machine timer. With a pressure trigger, a patient effort pulls airway/circuit pressure negative and mechanical breaths are initiated when pressure exceeds the set negative pressure threshold (pressure sensitivity). With a flow trigger, a patient effort draws flow from the circuit (often from a continuous bias flow) and mechanical breaths are initiated when flow into the patient exceeds the set flow threshold (flow sensitivity). In Figure 7 are illustrated three different triggering episodes. The pressure triggering threshold is indicated by a negative pressure level below baseline; the flow triggering threshold is indicated by an inspiratory flow above baseline bias flow.

12. A B C Pressure Limited Flow Limited Flow Limited Volume Limited
Limit variable means restricting the magnitude of a variable during inspiration. A limit variable is one that can reach and maintain a preset level before inspiration ends (i.e. it does not end inspiration). Pressure, flow or volume can be limit variable but time cannot be a limit variable because limiting inspiratory time would cause inspiration to end. A limit variable does not terminate inspiration; it only sets an upper bound for pressure, flow or volume (Figure 8).
Volume Limited

13. A B C Time Cycled Volume Cycled Time Cycled Set Time Set Time
Cycle variables determine how a breath is ended. A positive pressure breath will always end because a variable has reached a set value; this can be pressure, volume, flow or time. When a ventilator is set to pressure cycle, it delivers the flow until a preset pressure is reached, at which time inspiratory flow ends and expiratory flow begins. When a ventilator is set to volume cycle, it delivers the flow until a preset volume has passed through the control valve, at which time inspiratory flow stops and expiratory flow begins. The flow may be used to terminate the inspiratory phase when it reaches a preset level usually 25% of the maximum inspiratory flow, at which time the inspiration ends. A pressure-cycled ventilator is one that stops pushing gas into a patient’s lungs when a preset airway pressure is reached. An example of a pressure-cycled ventilator is a Bird ventilator, which is commonly used to give intermittent positive pressure breathing (IPPB) treatments. The major disadvantage of pressure-cycled ventilators is that they will not deliver the desired tidal volume if pulmonary compliance is decreased. Time cycling means that expiratory flow start because a preset inspiratory time has elapsed (Figures 9 and 10).
Set Volume

14. D E F Flow Cycled Pressure Cycled Flow/Time Cycled Set Pressure
Set Flow Cycle at 25%
Of Peak Inspiratory Flow
Set flow cycle at 25% of
peak inspiratory flow was
not reached
Back Up Time Cycle is activated

15. Mechanical Ventilation Graphical Assessment
Other Settings

16. Set respiratory rate= 12/min
60 seconds/12 = 5 seconds for each respiratory cycle
Set: 1.5 seconds
3.5 seconds
I:E Ratio = 1:2.3
Set respiratory rate= 15/min
60 seconds/15 = 4 seconds for each respiratory cycle
Set: 1.5 seconds
2.5 seconds
Ventilators also exert control over flow and time. Time is based on ventilatory rate. Other time functions the ventilator may control are inspiratory (I) and expiratory (E) time and the subsequent I:E ratio. Once the respiratory rate is set, the ventilator will calculate the respiratory cycle duration by dividing 60 seconds over the set rate, the expiratory time is determined by subtracting the respiratory cycle time from the set inspiratory time, subsequently I:E ratio can be determined (Figure 5).
I:E Ratio = 1:1.6

17. Set respiratory rate= 12/min
60 seconds/12 = 5 seconds for each respiratory cycle
Set: 1.5 seconds
3.5 seconds
I:E Ratio = 1:2.3
Inspiratory Flow Time
Inspiratory Hold Time
Ventilators also exert control over flow and time. Time is based on ventilatory rate. Other time functions the ventilator may control are inspiratory (I) and expiratory (E) time and the subsequent I:E ratio. Once the respiratory rate is set, the ventilator will calculate the respiratory cycle duration by dividing 60 seconds over the set rate, the expiratory time is determined by subtracting the respiratory cycle time from the set inspiratory time, subsequently I:E ratio can be determined (Figure 5).
Inspiratory Time
Expiratory Time

18. Same Set IInspiratory Time
Higher Set Flow Rate
Longer Inspiratory Hold Time
Flow rate in flow controlled ventilation determines the inspiratory flow time, if the set tidal volume is delivered in a less time than the set inspiratory time, the remaining time is called the inspiratory hold time that represents the plateau phase of inspiration with a zero flow. If the flow rate is increased, the set tidal volume is delivered in a shorter time and higher peak pressure, the inspiratory hold time increases and the inspiratory flow time shortens (Figure 6).
Shorter Inspiratory Flow Time

19. TI TE

20. VT 3 VT 1 Insp Exp VT 2 Ti a Flow= 37.5 L/min Flow= 30 L/min

21. Flow= 60 L/min
Flow= 30 L/min
Flow= 20 L/min
1.5 sec
1 sec
0.5 sec

22. Exponential-decay
Rectangular
Ascending-ramp
Sinusoidal

23. Mechanical Ventilation Graphical Assessment
Breath Types

24. A B C D Pressure Limited Patient Triggered Patient Triggered
Time Triggered
Patient Triggered
Flow Control
Flow Control
Flow Cycled
Patient’s Flow
Time Cycle
Patient’s Cycle
Volume Cycle
Spontaneous Breath
Supported Breath
Assisted Breath
Mandatory Breath

25. Mechanical Ventilation Graphical Assessment
Breath Sequences

26. Continuous Mandatory Ventilation50
cmH2O
PAW
Continuous Mandatory Ventilation 50
cmH2O
PAW
Intermittent Mandatory Ventilation 50
cmH2O
PAW
Continuous Spontaneous Ventilation

27. Mechanical Ventilation Graphical Assessment
Modes of Ventilation

28. Controlled Mechanical Ventilation (CMV): With CMV, all breaths are totally controlled by the ventilator, and patient triggering is not possible. CMV is also called volume controlled ventilation (Figure 17) or pressure-controlled ventilation (Figure 18). In some ventilators, the only difference between CMV and assist-control ventilation is the sensitivity setting. In reality; assist-control or intermittent mechanical ventilation modes can provide controlled mechanical ventilation if the patient is sedated and/or paralyzed. With volume-targeted CMV, the clinician sets the rate, tidal volume, flow waveform, peak inspiratory flow or inspiratory time and I:E ratio. With pressure target ventilation, the clinician sets the rate, pressure level, inspiratory time, or I:E ratio.

30. Assist-Control Ventilation (ACV) may be eaither pressure or volume targeted. With ACV, a minimal rate and tidal volume (or inspiratory pressure) are set by the clinician. The patient may trigger the ventilator at a more rapid rate, but the clinician-determined tidal volume (or inspiratory pressure) is delivered.

31. Assisted Mechanical Ventilation (AMV), all breaths are triggered by the patients (no set backup rate) and each breath is delivered at the ventilator’s set tidal volume or (pressure)

32. Synchronized Intermittent Mandatory Ventilation (SIMV), This mode of ventilation is similar to IMV and available with pressure (Figure 22) or volume (Figure 23) targeting, except that the ventilator deliverd the mandatory breath in sunchrony with the patient’s inspiratory efforts, and gas is supplied by a patient-triggered demand system during spontaneous breaths. In essence, the unit functions in the assist-control mode only during “windows” of time established by the manufacturer. If a patient’s inspiratory effort is detected while the window is open, asynchronized breath is delivered. If no patient effort is detected at the time the window closes, the vemylator delivers a mandatory brath.This avoids the stacking of mandatory breath on top of aspontaneous breath. In addition pressure support can be provided during spontaneous breathing with either pressure- or volume-targeted SIMV (Figure 24).

33. Synchronized Intermittent Mandatory Ventilation (SIMV), This mode of ventilation is similar to IMV and available with pressure (Figure 22) or volume (Figure 23) targeting, except that the ventilator deliverd the mandatory breath in sunchrony with the patient’s inspiratory efforts, and gas is supplied by a patient-triggered demand system during spontaneous breaths. In essence, the unit functions in the assist-control mode only during “windows” of time established by the manufacturer. If a patient’s inspiratory effort is detected while the window is open, asynchronized breath is delivered. If no patient effort is detected at the time the window closes, the vemylator delivers a mandatory brath.This avoids the stacking of mandatory breath on top of aspontaneous breath. In addition pressure support can be provided during spontaneous breathing with either pressure- or volume-targeted SIMV (Figure 24).

35. Contineous Positive Airway Pressure (CPAP), This is a spontaneous breathing mode No mechanical positive-pressure breaths are delivered. The only variables set by the clinician are the level of CPAP and the sensitivity of the demand system (Figure 25). CPAP is often confused with PEEP. CPAP is a specific mode of ventilation, whereas PEEP is the elevation of baseline system pressure during other positive-pressure modes of ventilation.

36. M M Tsupp Tsynch M Tsynch Mandatory Cycle Time Triggered window for
supported breaths
Triggered window for
synchronized breaths

37. Pressure-Controlled Inverse-Ratio Ventilation (PCIRV), PCIRV is a variation of PCV in which inspiration is longer than expiration. PCIRV is typically initiated by selecting PCV and adjusting settings to provide the desired I:E ratio or inspiratory time (Figure 26).

38. Airway Pressure Release Ventilation (APRV), APRV is described as two levels of CPAP (high and low) that are applied for defined periods of time where spontaneous breathing is allowed at both levels. Normally the inspiration time is much longer than the inspiration time, the clinician sets the two levels of CPAP and the time spent at each level (Figure 27).

39. Bilevel Airway Pressure Ventilation (Bilevel))
Bilevel Airway Pressure Ventilation (Bilevel)). Bilevel is a modification of APRV. The patient’s spontaneous breathing efforts and the change from one CPAP level to the other are coordinated. As a result, breath stacking is avoided. In addition, pressure support can be added to the spontaneous breaths at either or both levels of CPAP (Figure 28).

40. Pressure Support Ventilation (PSV)
Pressure Support Ventilation (PSV). This is a pressure targeted mode where the patient’s inspiratory efforts are supported by the ventilator at a preset level of inspiratory pressure. Inspiration is initiated by the patient and terminated primarily when inspiratory flow falls to a ventilator-specific level (Figure 29). During PSV, the patient determines the inspiratory rate, inspiratory time, and tidal volume; the ventilator only controls the inspiratory pressure level. PSV can be combined with SIMV (Figure 30) and applied to the spontaneous breaths during bilevel pressure ventilation (Figure 31). Breaths are triggered only by the patient, the ventilator delivers sufficient flow to rapidly achieve the set pressure level. After the pressure is established flow must decrease rapidly to ensure that the pressure dose not exceed the set level. When the flow decreases to the target cycling level (normally 25% of the peak flow), ventilator inspiration is terminated.

44. Pressure Limit
Pressure Alarm Limit
Pressure Adjusted 2-3 cm H2O each
breath to Achieve Target Volume
Pressure Maintained
5 cm H2O Test Breath
Pressure Decreased
Higher Tidal Volume
Set Tidal Volume
Tidal Volume Still
Lower than Target
Target Tidal Volume
Achieved
Low Tidal Volume

45. Thank you