Basic Principles of Critical Care

1. BASICS OF MECHANICAL VENTILATION
Gradian Health Systems
Basic Principles of Critical Care
RESPIRATORY SYSTEM

2. Disclaimer
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation
Disclaimer: Gradian Health Systems cannot provide formal recommendations or indications
regarding medical care and clinical service delivery. The tables, checklists, and other clinical
documents referenced in this training have not been validated in all settings. These documents are
intended to serve as examples only. We recognize that all clinical training content and activities
must be customized to meet the needs of each facility and its clinical staff, factoring in available
resources, practitioner skill level, and other environmental considerations.
For any questions regarding the contents or applications of this training,
please contact Gradian Health Systems:
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training@gradianhealth.org

3. Module 2
Gradian Health Systems
Basics Principles of Critical Care
Respiratory System

4. Module 2: Respiratory System
MODULE OVERVIEW
Lesson 1 I Respiratory System Anatomy and Physiology
Lesson 2 I Oxygen Therapy
Lesson 3 I Evaluation of the Respiratory System
Lesson 4 I Airway Equipment and Management
Lesson 5 I Invasive and Non-invasive Ventilation
Lesson 6 I Basics of Mechanical Ventilation
Lesson 7 I Ventilator Modes and Settings
Lesson 8 I Ventilation Complications
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

5. Components of the Gradian CCV SystemLesson 6: Basics of Mechanical Ventilation
Lesson Objectives
• Describe the basics of ventilator machines
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

6. Components of the Gradian CCV SystemLesson 6: Basics of Mechanical Ventilation
Key Concepts
• Trigger
• Limit
• Cycle
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

7. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
What is a ventilator?
Devices that generate a breath by integrating volume, pressure, time and flow.
Breath is delivered are based in four phases:
• Trigger phase – how the breath is initiated
• Inspiratory phase – mainly dealing with the flow of gas into the lungs, or how
the breath gets delivered
• Cycle phase – when inspiration ends, and expiration begins
• Expiratory phase – mainly dealing with the baseline pressure during the
period between breaths
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

8. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Definitions of Key Terms
• Trigger –what starts the breaths can be determined by pressure or flow
• Limit – what determines the size of the breath (volume, time, pressure)
• Cycle – what ends the breath (time or volume)
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

9. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Trigger
Trigger phase determines how the mechanical breath is initiated and can be from
the machine (mandatory) or from the patient (spontaneous). There are several
methods of triggering. The most common are:
• Time triggering – breaths initiated after a set time
• Pressure triggering – breath initiated when a set negative pressure is
detected by the machine
• Flow triggering – when the patient takes a breath and air flow is detected
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

10. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Time-triggered Ventilation
Ventilator is set to deliver a breath a certain time after expiration.
For example, if the ventilator is set at 10 breaths per minute, the machine will
deliver a breath every 6 seconds. Time-triggered is always mandatory because
the breaths are delivered regardless of whether the patient is taking breaths.
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation
Disadvantages
• Machine and patient may not
synchronize
• Patient must be adequately sedated
• May lead to deconditioning
Advantages
• Guaranteed breaths per minute
• Minute volume can be calculated
• Patient does not need to trigger the
ventilator

11. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Pressure-triggered Ventilation
Ventilator detects the drop in negative pressure at the start of the patient's own
inspiratory effort. The amount of pressure needed to trigger a breath is called the
trigger sensitivity and is set on the machine in cmH2O.
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

12. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Flow-triggered Ventilation
Ventilator initiates the breath after detecting a drop in baseline flow or a change
in flow. A flow trigger can be set on the machine in liters per minute or as a
decrease in pressure (e.g. trigger pressure can be set over a range of -20 to
+10). The pressure flow trigger is more comfortable for the patient because it
requires less work of breathing. However, it may also be too sensitive that it
leads to auto-triggering where a change in flow is perceived but caused by
something other than the patient (e.g. from cardiac activity).
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

13. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Limit Variable
This is set as the maximum level that can be achieved by the ventilator during
inspiration. The variable does not cause the breath to end. This can either be a
flow rate or an inspiratory pressure. If a flow rate is set on the machine at 60
L/min, the flow will not go higher than that during inspiration and the machine will
adjust the inspiratory pressure to achieve the set parameters.
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

14. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Cycle Variable
This is the parameter that the ventilator uses to end inspiration or begin
expiration. There are four cycling variables:
• Pressure
• Time
• Volume
• Flow
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

15. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Pressure Cycling
When the set pressure level is reached the ventilator end inspiration and begins
expiration. This prevents high sustained inspiratory pressure and can be used as
a protective measure.
Time Cycling
The ventilator starts expiration when the set time is achieved. The time that is
dependent on the set respiratory rate, or the I:E ratio.
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation

16. Components of the Gradian CCV SystemBasics of Mechanical Ventilation
Volume Cycling
When the set volume is reached the machine initiates the expiratory phase.
Flow Cycling
This is set as a percentage decrease of the inspiratory flow rate. Flow cycled
ventilation is used in spontaneous modes.
Basic Principles of Critical Care Training I Basics of Mechanical Ventilation