MECHANCIAL VENTILATIONTHREE TRIGGER, THREE BREATHS & THREE MODES (PART ONE)

MECHANCIAL VENTILATION

Objectives:

• To provide the building blocks for a deeper understanding of mechanical ventilation

• ③ Trigger• ③ Types of Breaths• ③ Modes

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

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.

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

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

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.

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

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

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

THREE TYPES OF BREATHSMore review:

• There are two common combinations of breath types:

Assisted & Controlled (AC)

Spontaneous (PSV)

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

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.

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.

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.

THREE MODES & THREE TYPES OF BREATHS

MV

Volume Control (AC or CMV)

Controlled Breaths

Assisted Breaths

Pressure Control (AC-PC or PCV)

Controlled Breaths

Assisted Breaths

Spontaneous

Spontaneous Breaths

Mechanical Ventilation

Three Modes

Three Breath Types

Ventilator Trigger (Time)

Ventilator Trigger (Time)

Patient Trigger (Flow or Pressure)

Patient Trigger (Flow or Pressure)

Patient Trigger (Time)

MECHANCIAL VENTILATION

TRIGGER: TIME / FLOW / PRESSURE

BREATHS: ASSISTED / CONTROLLED / SPONTANOUS

+

=VOLUME-CONTROL / PRESSURE-CONTROL /PRESSURE SUPPORT

MECHANCIAL VENTILATION

• That is a lot of information!

• Your doing great!

• Let us move on to part two: respiratory cycle