Basic modes of mv

Basic
Modes of
MV
Mostafa
Elshazly
Professor Of Pulmonary
Medicine
Chairman Of Pulmonary Critical
Care Unit (PCCU)
Kasr Alainy School Of Medicine
Cairo University
elshazly66@Hotmail.com

Invasive Mechanical
Ventilation Workshop

• Normal breathing is composed of an infinite range of
breaths that vary in depth and timing to suit any and
every circumstance from sleeping, yawning or coughing to
singing or running.

• Mechanical substitution of the natural act of breathing
could never hope to match what nature has achieved, but
within the ICU ventilator we do have at our disposal a
range of breath types that are characterized by properties
that fall into two principle domains, those of cycling and
inspiratory motive force.

• The cycling properties of a breath describe what
makes the breath start, what makes the breath end
and describes the relationship the breath has with
other breaths.
an active ‘flow’ (TI flow )
an end-inspiratory pause (TIpause )

• The cycling properties of a breath describe what
makes the breath start, what makes the breath end
and describes the relationship the breath has with
other breaths.

• The inspiratory motive force simply refers to the
mechanism the ventilator uses to drive gas into the lungs.

Ventilatory Support
FULL PARTIAL
All energy provided by ventilator
e.g. ACV / full support SIMV ( RR
= 12-26 & TV = 8-10 ml/kg)
Pt provides a portion of energy
needed for effective ventilation
e.g. SIMV (RR < 10)
Used for weaning
WOB total = WOB ventilator (forces gas into lungs)+ WOB patient (msls draw gas into
lungs)

What Is A ‘ Mode Of Ventilation’ ?
• A ventilator mode is delivery a sequence of
breath types & timing of breath

Inspiratory Cycling
Triggering
• Inspiratory cycling that is determined by the ventilator usually
occurs because a certain amount of time has elapsed since the last
breath.
• Alternatively inspiratory cycling can be at the patient’s instigation

Inspiratory Cycling
Triggering ( manual)

Inspiratory Cycling
Triggering ( machine)

Inspiratory Cycling
Triggering (Patient)
• They are pressure trigger sensitivity and ﬂow trigger
sensitivity .

Inspiratory Cycling
Triggering (Patient)

Expiratory Cycling
• Expiratory cycling can be based on either time or
flow.

Expiratory Cycling
• Ventilator allows exhalation to begin when a preset inspiratory
time has ended and a preset tidal volume or a preset inspiratory
pressure has been reached.
1. Time Cycled

Expiratory Cycling
• Ventilator allows exhalation to begin when inspiratory ﬂow
decreases to a preset expiratory trigger.
• Flow-dependent expiratory cycling can only operate when
inspiration is PSV.
• IFR rises rapidly to a peak and then falls exponentially.
• When the IFR falls below a specific threshold, measured as a
percentage of the PIF , the ventilator cycles into expiration
2. Flow Cycled

Expiratory Cycling
• Ventilator allows exhalation to begin when inspiratory ﬂow
decreases to a preset expiratory trigger.
2. Flow Cycled

Inspiratory Motive Force
• During inflation, a MV causes gas to flow into a patient’s
lungs and it can only do so by creating a pressure gradient
between the upper airway and the alveoli.

• In each case, one variable is the primary, independent variable
whose change in value is predetermined, and the other is the
secondary, dependent variable whose change in value can only be
measured.
• In other words, to effect PPV, we can either choose to deliver a
predetermined volume and accept the pressure change that this
causes, or effect a predetermined pressure change and accept the
volume that this delivers.

• Pressure
• Volume
• Dual control
• Occurs in situations where inspiration starts out as volume
control and then switches to pressure control before the end of
the breath (or vice versa).

• Volume as the drive to inspiration
• With VCV, the Vt is preset and the ventilator generates the
flow required to deliver this volume in the available Ti , with
the airway pressure being entirely dependent on the Raw &
C of the respiratory system.

• Volume as the drive to inspiration

• Pressure as the drive to inspiration
• In PCV, the airway pressure generated during inspiration is set
with the resulting Vt depending upon the respiratory system
compliance and resistance.

• Multi-parameter breaths
• Most intensive care ventilators now offer dual parameter modes
that combine the volume guarantees of VCV with the pressure
and flow characteristics of PCV.

Classification of modes
 Broadly speaking, modes fall into four categories,
as described above:
 Mandatory,
 Triggered,
 Spontaneous and
 Hybrid modes
Within these categories the wide and
often confusing range of PPV modes
offered by the modern intensive care
ventilator can be understood by
considering the following key elements:

Classification of modes
 Broadly speaking, modes fall into four categories,
as described above:
 Mandatory,
 Triggered,
 Spontaneous and
 Hybrid modes
➢ What determines Trigger?
➢ What drives control parameter
➢ Is feedback intra-breath or inter-breath?
➢ What determines cycling?

Classification of mode
• Mandatory Modes
• Continuous Mandatory Ventilation (CMV) is the simplest mode of
ventilatory support.
• Vt & RR are fixed and there is no synchronization with the
patient’s respiratory efforts.

• Mandatory Modes
• Continuous Mandatory Ventilation (CMV) is the simplest mode of
ventilatory support.
• PIP &Ti are fixed and there is no synchronization with the
patient’s respiratory efforts.

• Mandatory Modes

• Mandatory Modes
• Volume-targeted pressure control combines the benefits of
volume and pressure control
• The volume is set, but rather than being delivered as a constant flow rate for a set
period of time, it is delivered as a pressure-controlled breath with a square wave of
pressure and a decelerating flow rate.

• Triggered Modes
• Pressure Support

• Triggered Modes
• Pressure Support
• Spontaneous breathing is assisted with an increase in airway
pressure following each inspiratory effort .
• The ventilator continues to deliver the breath until the inspiratory
flow has decreased to a specific level (e.g., at 25% of the peak
inspiratory flow) (flow cycle-off).

• Triggered Modes
• Volume-targeted pressure support (VS )
• Is a modification of pressure support and can be considered a dual
parameter mode applied to a support mode.

• Triggered Modes
• Proportional assist ventilation(PAV )
• Is a modification of pressure support and can be considered a dual parameter
mode applied to a support mode.
• The degree of support varies according to patient effort such that with
increasing patient effort more support is provided. It has been described as the
ventilator equivalent of power steering.

• Triggered Modes

• Assist control
• In AC the patient is able to trigger ventilator breaths
• Vt & RR are set as in CMV. However, the set frequency should be considered
as the minimum or back-up rate that the ventilator will deliver if the patient
makes no respiratory efforts when the mode is effectively identical to CMV.
• However, if the patient makes an inspiratory effort, the ventilator delivers a
breath of the set tidal volume.
Hybrid Modes

• Synchronized intermittent mandatory ventilation
• This ventilation mode is a transition from assist-controlled (A/C) ventilation
mode to pressure support ventilation (PSV) mode.
• So, the type of breath that is delivered is a combination of mandatory breath,
assisted breath, and pressure support.
Hybrid Modes

• Cycle of SIMV is divided into two parts:
• SIMV period
• Spontaneous period
Hybrid Modes

• SIMV period
• Patient trigger in AC trigger window will deliver assisted breath while in
inspiratory time Ti.
• If there is no patient trigger until assist control trigger window has elapsed,
the mandatory breath will be delivered while in inspiratory time Ti.
Hybrid Modes

• SIMV period
• Spontaneous period
• Every patient trigger of spontaneous breath while in spontaneous
period will be given and supported by pressure support. Spontaneous
period ends when the SIMV cycle ends.
Hybrid Modes

Hybrid Modes

• bi-level ventilation
• In its simplest form, bi-level ventilation can be likened to a form of CPAP in
which the level of CPAP cycles between two different pressures with the
phase transitions synchronized to the patient’s inspiration and expiration
Hybrid Modes

• The patient’s spontaneous breathing activity is unsupported and the user
simply sets the duration (Thigh) and pressure (Phigh) for the high-pressure
phase as well as the duration (Tlow) and pressure (PEEP) for the low-
pressure phase.
Hybrid Modes

• More recent implementations of the bi-level concept have added pressure
support to breaths triggered during the low-pressure phase or during both
low and high phases .
• The ability to maintain spontaneous ventilation throughout all phases of
ventilation is claimed to improve comfort as it prevents the patient ‘fighting
the ventilator’.
Hybrid Modes

• Airway pressure release ventilation
• APRV is a variant of bi-level ventilation where a relatively high airway
pressure is maintained for a prolonged period with brief episodes when the
airway pressure falls to a lower value .
• Spontaneous ventilation is maintained throughout. APRV maintains a high
mean airway pressure promoting lung recruitment and is an effective method
of improving oxygenation in patients with severe ARDS .
Hybrid Modes

Basic modes of mv

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