Chapter 46 PowerPt

Chapter 46: Mechanical Ventilators

Learning Objectives (1 of 2)

  • Define a mechanical ventilator.

  • Describe the key design features of ventilator displays.

  • Discuss the importance of properly setting alarm thresholds.

  • Explain how the compliance of the patient circuit affects volume delivery.

  • Describe the 10 maxims used to develop a standardized ventilator taxonomy.

Learning Objectives (2 of 2)

  • Define the four different types of intermittent mandatory ventilation.

  • Demonstrate how to classify any mode of ventilation.

  • List the three main goals of mechanical ventilator support.

  • Discuss the differences between conventional and high-frequency ventilators.

Introduction

  • To safely and effectively initiate and manage a mechanical ventilator, the Respiratory Therapist (RT) must thoroughly understand:

    • Ventilator Design: Understanding the structural and functional design.

    • Classification and Operation: Different modes and their applications.

    • Clinical Application: Appropriate application of ventilatory modes in clinical settings.

    • Physiologic Effects: Understanding gas exchange and pulmonary mechanics associated with mechanical ventilation.

How Ventilators Work (1 of 2)

  • A mechanical ventilator is defined as:

    • A machine designed to perform some portion of the work of breathing.

    • It delivers various medical gas mixtures to the patient.

    • Modern ventilators utilize sophisticated software and advanced monitoring systems to:

    • Deliver diverse breathing patterns tailored to meet patients' safety, comfort, and eventual liberation needs.

How Ventilators Work (2 of 2)

  • Power Source for a Ventilator:

    • Primarily derived from electrical energy and compressed gas.

  • Drive Mechanism:

    • Converts the input power into useful work.

  • Control Circuit:

    • Adjusts output to augment or replace the patient’s muscles in performing work of breathing.

Operator Interface (1 of 2)

  • Most ventilators are equipped with digital displays.

  • Common features include:

    • LED Screens: Display ventilator data with multipurpose hard-wired buttons.

    • Advanced Displays: May include computer touch screens for detailed visual data representation.

Operator Interface (2 of 2)

  • “Virtual” Instrument:

    • Interface simulates knobs, buttons, dials, and meters on the screen,

    • May rely on a single mechanical dial and a few buttons to set various parameters.

Ventilator Displays (1 of 3)

  • Ventilator displays serve three main functions:

    • Input Display: Shows the current state of settings and allows for changes.

    • Output Display: Shows measured values that characterize normal patient-ventilator interactions.

    • Alarm Conditions: Notifies clinicians of any alarm triggers.

Ventilator Displays (2 of 3)

  • Alphanumeric Values:

    • Include measured or calculated data related to ventilatory support; typical values are:

    • FiO2 (Fraction of inspired oxygen)

    • Pressures (peak inspiratory and expiratory)

    • Volumes and frequency

    • I:E ratio (Inspiratory to Expiratory ratio)

    • Percent leak, resistance, and compliance.

  • Trends:

    • Clinicians can track measured or calculated data related to ventilator support over time.

Ventilator Displays (3 of 3)

  • Waveforms and Loops:

    • Graphical displays of pressure, volume, and flow to help determine causes of patient-ventilator asynchrony.

  • Picture Graphics:

    • Visual representations of the patient-ventilator systems.

  • Alarm Settings:

    • Essential for bringing attention to significant clinical events.

The Patient Interface

  • Defined as:

    • The connection between the ventilator and the patient, typically through a system of plastic hoses referred to as the patient circuit.

  • Impact of Patient Circuit:

    • Contributes to discrepancies between desired and actual ventilator output values, notably during volume-controlled ventilation.

Identifying Modes of Mechanical Ventilation

  • Manufacturers often use unique names for modes without industry standards, causing challenges:

    • Different names for modes that function similarly can confuse clinicians.

The 10 Maxims for Understanding Modes

  • A formal taxonomy exists for classifying modes of ventilation:

    • Comprised of 10 fundamental maxims, which are concise statements of scientific principles.

The 10 Maxims for Understanding Modes (1 of 12)

  • Maxim 1: A breath is defined as one cycle of positive flow (inspiration) and negative flow (expiration).

    • Key definitions include:

    • Inspiratory time: Period from the start of inspiratory flow to the start of expiratory flow.

    • Expiratory time: The time from the start of expiratory flow to the start of inspiratory flow.

The 10 Maxims for Understanding Modes (2 of 12)

  • Maxim 2: A breath is assisted if the ventilator provides some or all of the work of breathing.

    • Defined in terms of pressure required to deliver tidal volume:

    • The pressure change during inspiration times the volume change.

The 10 Maxims for Understanding Modes (3 of 12)

  • Maxim 3: A ventilator assists breathing using either pressure control or volume control.

    • Based on the equation of motion for the respiratory system:

    • Volume control: Volume and flow preset prior to inspiration.

    • Pressure control: Inspiratory pressure preset to a constant value or proportionate to inspiratory effort.

    • Time control: All parameters depend on changing respiratory mechanics, with only inspiratory and expiratory times predetermined.

The 10 Maxims for Understanding Modes (4 of 12)

  • Maxim 4: Breaths are classified by the criteria that trigger and cycle inspiration.

    • Trigger signals can include:

    • Time

    • Changes in airway pressure, volume, or flow.

    • Electrical signals from the diaphragm.

The 10 Maxims for Understanding Modes (5 of 12)

  • Maxim 5: Trigger and cycle events can originate from either patient or machine.

    • Types of Triggering:

    • Patient Triggering: Starting inspiration based on a patient's independent signal.

    • Machine Triggering: Starting inspiratory flow based on a ventilator signal.

    • Types of Cycling:

    • Patient Cycling: Ending inspiratory time based on patient-determined signals.

    • Machine Cycling: Ending time independent of patient-determined signals.

The 10 Maxims for Understanding Modes (6 of 12)

  • Maxim 6: Breaths classified as spontaneous or mandatory based on trigger and cycle events.

    • Spontaneous Breath: Triggered and cycled by the patient.

    • Mandatory Breath: Any breath that is not spontaneous (includes all variations of patient and machine initiations).

The 10 Maxims for Understanding Modes (7 of 12)

  • Maxim 7: Three basic breath sequences:

    1. Continuous Mandatory Ventilation (CMV):

    • No spontaneous breaths can occur between mandatory breaths; total frequency must always be equal to or above the set frequency.

    1. Intermittent Mandatory Ventilation (IMV):

    • Mandatory breaths delivered at set frequency or only when spontaneous frequency is below a certain threshold.

    1. Continuous Spontaneous Ventilation (CSV):

    • All breaths are spontaneous.

The 10 Maxims for Understanding Modes (8 of 12)

  • Maxim 8: There are five basic ventilatory patterns:

    • (1) VC-CMV

    • (2) VC-IMV

    • (3) PC-CMV

    • (4) PC-IMV

    • (5) PC-CSV

    • Each is characterized by designated control variables (either volume or pressure) for mandatory or spontaneous breaths.

The 10 Maxims for Understanding Modes (9 of 12)

  • Maxim 9: Ventilatory patterns can be distinguished by targeting schemes:

    • Types include:

    • Set-point, dual, bio-variable, servo, adaptive, optimal, and intelligent.

The 10 Maxims for Understanding Modes (10 of 12)

  • Maxim 10: Classification of a ventilation mode according to:

    • Control variable (pressure or volume)

    • Breath sequence (CMV, IMV, CSV)

    • Targeting schemes

    • A ventilation mode is a predefined interaction between the ventilator and patient, aiding clinical comparisons and optimizing ventilator management.

The Taxonomy for Mechanical Ventilation (1 of 2)

  • Taxonomy Defined:

    • A hierarchy organizing concepts from general to specific levels.

    • The ventilator mode taxonomy encompasses four hierarchical levels:

    1. Control variable (pressure or volume)

    2. Breath sequence (CMV, IMV, CSV)

    3. Primary breath-targeting scheme (for CMV or CSV)

    4. Secondary breath-targeting scheme (for IMV)

The Taxonomy for Mechanical Ventilation (2 of 2)

  • When classifying ventilation modes, clinicians must follow these steps:

    • Step 1: Identify the control variable.

    • Step 2: Identify the breath sequence.

    • Step 3: Identify the targeting schemes for primary (and optionally secondary) breaths.

Comparing Modes of Mechanical Ventilation

  • Clinicians need to understand both the tool and its usage:

    • Goals:

    • Safety: Ensure adequate gas exchange and hemodynamics while avoiding atelectrauma and volutrauma.

    • Comfort: Optimize patient-ventilator synchrony.

    • Liberation: Facilitate timely withdrawal from the ventilator with minimal adverse events.

Types of Ventilators

  • Conventional Ventilators:

    • Produce breathing patterns close to physiologic normal values, with a max breath rate limit of 150 breaths per minute.

  • High-Frequency Ventilators:

    • Generate respiratory frequencies much higher than physiologically possible, with tidal volumes lower than anatomical dead space.

Ventilator Classification by Use (1 of 2)

  • Critical Care Ventilators:

    • Complex breath delivery methods and advanced monitoring capabilities.

  • Subacute Care Ventilators:

    • Less sophisticated monitoring systems positioned between critical care and home care devices.

  • Home Care Ventilators:

    • Support patients’ ventilatory needs while providing supplemental oxygen using simpler interfaces.

Ventilator Classification by Use (2 of 2)

  • Transport Ventilators:

    • Lightweight, compact, and durable with reliable power supply and low gas consumption.

  • Noninvasive Ventilators:

    • Can be integrated into various ventilators to enhance patient comfort.