How three triggers, three cycles (volume/pressure/flow) and three breaths types are used to make the basic modes of mechanical ventilation.

1. MECHANCIAL VENTILATION
THREE TRIGGER, THREE BREATHS & THREE MODES (PART ONE)

2. MECHANCIAL VENTILATION
Objectives:
• To provide the building blocks for a deeper
understanding of mechanical ventilation
• ③ Trigger
• ③ Types of Breaths
• ③ Modes

3. THREE TRIGGERS
• The trigger, or the
sensitivity, initiates
the respiratory cycle.
• The respiratory cycle
can be: time
(seconds), pressure
(cmH20), or flow
(lpm) triggered
Trigger
(Sensitivity)
Time
FlowPressure

4. THREE TRIGGERS
• Time Trigger:
The respiratory cycle will be initiated after a set period of time . For
example, if the rate is 15 a time cycled breath will be delivered every 4
seconds. No effort is require by the patient.
• Flow:
The respiratory cycle will begin when the patient inspiratory effort
generates a negative flow.
• Pressure:
The respiratory cycle will begin when the patient inspiratory effort
generates a negative pressure drop.

5. THREE TRIGGERS
• For sedated patients most ventilator allow a
combination of time / flow or time / pressure
triggered breaths.
• For awake patients, most ventilators allow only flow
or pressure triggered breaths.
• The pressure (or flow) trigger is manipulated by the
RT based on the clinical situation.
• Most modern ventilators are flow / time triggered.
• This concept will become clearer when we discuss the
three types of breaths.
③

6. THREE TYPES OF BREATHS
• Ventilators are only
capable of delivering
three types of
breaths: controlled,
assisted, and
spontaneous.
• In general, a
ventilator can deliver
controlled & assisted
breaths or
spontaneous
breaths.
• In mixed modes
some ventilators can
deliver controlled
and spontaneous
breaths.
Breath
Types
Assisted
SpontaneousControlled

7. CONTROL BREATHS
• Controlled breaths require no effort from the patient
(no work of breathing).
• Therefore, a controlled breath must be time triggered.
5 seconds 5 seconds 5 seconds
For example, a paralyzed
and deeply sedated patient
(RASS-5) is being ventilated
12 times per minute, or once
every 5 seconds.

8. ASSISTED BREATHS
• Patient are not locked out from the ventilator.
• They can initiate their own respiratory cycle (flow or pressure
trigger).
• The ventilator coordinates with the patient’s respiratory effort.
5 seconds ∆ in pressure
5 seconds ∆ in flow 5 seconds
5 seconds
Patient is more awake a
breaths above the ventilator

9. SPONTANOUS BREATHS
• Spontaneous breaths are not time triggered.
• They require an inspiratory effort from the patient. They
are flow or pressure triggered.
• The inspiratory effort must be sufficient enough to trigger a
respiratory cycle.
∆ in flow ∆ in flow
∆ in pressure ∆ in pressure

10. THREE TYPES OF BREATHS
• In review:
• Controlled breaths are only time triggered.
• Assisted breaths are flow (lpm) or pressure
(cmH20) triggered. This allows the ventilator to
coordinate ventilation with the patient.
• Spontaneous breaths are flow (lpm) or pressure
triggered (cmH20). No time cycle controlled
breaths are allowed.
• Most ventilators on 5.2 and 3A are time & flow
triggered and deliver controlled/assisted breaths
(i.e. AC or PCV) or spontaneous breaths (i.e. PSV).
③

11. THREE TYPES OF BREATHS
More review:
• There are two common
combinations of breath
types:
Assisted & Controlled
(AC)
Spontaneous (PSV)

12. MODES OF MECHANICAL VENTILATION
• How dose this all fit?
• The three triggers and three
breath types are the
building blocks for the three
– Volume-Control Ventilation
(AC-VC) (VC) (CMV)
– Pressure-Control Ventilation
(AC-PC) (PCV)
– Pressure-Support Ventilation
(PSV)
MV
Volume-
Control
Pressure-
Control
Pressure-
Support

13. VOLUME-CONTROLLED VENTILATION
• Volume control (AC-VC) will deliver a set
number of controlled (or mandatory)
breath to a pre-set volume.
• Patients can trigger assisted breaths.
• Airway pressure (PIP/PLT) can vary
(therefore, may not be acceptable in
patient with poor lung compliance).
• The RT will set the rate, VT, FiO2, PEEP, I:E
and the trigger based on the patient’s
clinical condition.

14. PRESSURE-CONTROLLED VENTILATION
• Pressure-Control (AC-PC/ PCV) will deliver a set number of controlled (or
mandatory) breath to set pressure.
• Patients can trigger an assisted breaths.
• Airway pressure is fixed but the VT may vary.
• The RT will set the rate, peak inspiratory pressure, FiO2, PEEP, inspiratory
time, and the trigger based on the patient’s clinical condition.
• Pressure cycled (or limited) breaths are safer in patients with poor lung
compliance.

15. PRESSURE-SUPPORT VENTILATION
• Pressure-Support Ventilation (PSV / PS) will only deliver patient
triggered spontaneous breaths.
• The respiratory rate and VT will vary depending upon the patient.
• The inspiratory cycle will end (cycle) when the maximum airway
pressure is reached (PSV+PEEP) or the flow has fallen (< 25%).
• PSV is used in stable patients with an intact respiratory drive.
• The pressure support, Fio2, and PEEP are set by the RT.

16. THREE MODES & THREE TYPES OF BREATHS
Three Breath
Types
Three Modes
Mechanical
Ventilation
MV
Volume Control
(AC or CMV)
Controlled
Breaths
Assisted Breaths
Pressure Control
(AC-PC or PCV)
Controlled
Breaths
Assisted Breaths
Spontaneous
Spontaneous
Breaths
Ventilator Trigger (Time)
Ventilator Trigger (Time)
Patient Trigger (Flow or Pressure)
Patient Trigger (Flow or
Pressure)
Patient Trigger (Time)

17. MECHANCIAL VENTILATION
TRIGGER: TIME / FLOW / PRESSURE
BREATHS: ASSISTED / CONTROLLED / SPONTANOUS
+
=
VOLUME-CONTROL / PRESSURE-CONTROL /PRESSURE SUPPORT

18. MECHANCIAL VENTILATION
• That is a lot of information!
• Your doing great!
• Let us move on to part two: respiratory cycle