The document explains mechanical ventilation, outlining three triggers (time, flow, pressure) that initiate the respiratory cycle, and the three types of breaths (controlled, assisted, spontaneous) that ventilators can deliver. It describes how these concepts integrate into three ventilation modes: volume-control, pressure-control, and pressure-support. The content serves as foundational knowledge for understanding mechanical ventilation systems and their clinical applications.

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