Without reference, identify principles about
volume/pressure and high frequency
ventilators with at least 70 percent accuracy.

Purpose of Volume/Pressure Ventilators
◦ Device used to move gas into the lungs
◦ Required when
 Acute respiratory failure
 No absolute rule

Categories
◦ Based on the type of pressure used to move gas
into the lungs
◦ Negative pressure ventilators
 Apply a sub-atmospheric pressure around the
chest
 Air at atmospheric pressure is drawn in
 An example is an iron lung
 Major disadvantages
Cannot provide adequate ventilation in all patients
Problems with fit and comfort during long-term use
◦ Pressure ventilators
 Apply a positive pressure directly to the airway
 Similar to mouth-to-mouth artificial ventilation
 Provides better control over ventilation
 Most common
 Disadvantage is that the increased pressure in the
thoracic cavity decreases venous blood return to the heart

Patient Connection Methods
◦ Face mask
 Disadvantages
 Difficult to get a good seal
 Airway blockage may occur
 Acceptable for short term emergency use only
◦ Intubation
 A rigid tube inserted into the trachea
 Types
Endotracheal tubes may be inserted through the mouth or
nose
Tracheostomy tube is surgically inserted into the trachea
o Use a balloon-like cuff which seals against the walls of the
trachea
 All gas flow is through the intubation tube

Limiting Devices - Required to prevent
barotraumas (lung damage)
o
Pressure limiter
 Pressure developed by the drive mechanism may be
high enough to injure the lungs
 Methods
 Vent excess pressure
 End the inspiration completely
◦ Flowrate control
 When the generated pressure is high there must
be some means of controlling flow rate
 Methods
 Increasing resistance
 With injectors, decreasing the driving pressure

Phases of the Ventilation Cycle
◦ Inspiratory phase - moves gas into the lungs
◦ Changeover from inspiration to expiration
 Cycling mechanisms determine when to end an
inspiration and begin an expiration
 There are four ways of cycling the ventilator
into an expiratory phase
 Pressure cycled ventilators
o Inspiration is ended when a predetermined pressure is
reached
o Volume, flow rate, and inspiratory time may all vary from
one inspiration to another
Flow cycled ventilators
o Inspiration is ended when the flow of gas
into the patient falls below a specific point
o Volume, pressure, and inspiratory time may
vary from one inspiration to another
Volume cycled ventilators
o Inspiration is ended when a predetermined
volume of gas has been delivered to the
patient
o Pressure, flow rate, and inspiratory time may
vary from one inspiration to another
Time cycled ventilators
o Inspiration is ended after a predetermined time
o Volume, pressure, and flow rate may vary from one
inspiration to another
 Inspiratory supplemental functions
Sigh- a periodic deep breath, usually delivered 6 to 10
times an hour
Inflation hold
o It is a period of time at the end of an inspiration that the
lungs are kept inflated
o Also known as inspiratory hold, inspiratory pause, or
inspiratory plateau
◦ Expiratory phase
 Allows the lungs to empty
 Normally not restricted by the ventilator
 Adjuncts of the expiratory phase
Expiratory resistance
o Application of mechanical resistance to the exhalation port
of the breathing circuit
o Increases the mean airway pressure
◦ Positive end-expiratory pressure (PEEP)
 Maintains a positive pressure in the lungs
throughout the respiration cycle
 Used during mechanical breathing
 Purposes
Increases the mean airway pressure and functional
residual capacity
May improve lung compliance
◦ Continuous positive airway pressure (CPAP)
 Maintains a positive pressure in the lungs
throughout the respiration cycle
 Used during spontaneous breathing
 Purposes:
Keeps airways open
Increases the mean airway pressure and functional
residual capacity
◦ Changeover from expiration to inspiration
 Cycling mechanisms determine when to end an
expiration and begin an inspiration
 Three ways of cycling the ventilator into an
inspiratory phase
Manual cycling - expiration is ended and inspiration is
begun by operator intervention
Patient cycled
o
o
o
o
Started when the patient attempts to take a breath
Once initiated the ventilator delivers a controlled breath
Breath is known as an "assisted" breath
The sensitivity or trigger sensitivity parameter must be set
to the patient's efforts
Timed cycled
Inspiration begins after a predetermined time has passed
Timer is independent of the patient
Controlled by the "breaths/min" setting
Classified as a "strict controller" if no assist mechanism is
used
o Often used as a backup to patient cycling
o
o
o
o

Special Ventilator Modes
◦ Developed to make it less tedious to wean patient
from the ventilator
◦ Intermittent mandatory ventilation (IMV)
 Allows the patient to breathe spontaneously
between controlled breaths
 May be divided into two phases
IMV phase
Spontaneous phase
 Controlled IMV breath is delivered at the beginning
of the IMV phase
 Disadvantage is that the ventilator can inspire
against the patient
 Uncommon
◦ Synchronized intermittent mandatory ventilation
(SIMV)
 Allows the patient to breathe spontaneously
between assisted breaths, with a mandatory
breath as backup
 May be divided into two phases
SIMV phase
Spontaneous phase
Assisted breath in SIMV phase is synchronized to
patient efforts
If no assisted breath is taken during the SIMV phase
o A mandatory SIMV breath will be given
o At the beginning of the next spontaneous phase
◦ Mandatory minute ventilation (MMV)
• Additional option to SIMV
• Number of mandatory breaths is increased or decreased
dynamically
• Used to ensure a specific minute ventilation

High Frequency Ventilation (HFV)
◦ Uses breath rates of 1 HZ to 20 HZ
◦ Purpose
 Low diffusion
 Patient requires higher pO2 (partial pressure of oxygen) gradient
to force O2 to diffuse
 Allows the Paw to be reduced but keeps pO2 high
 Infants
 Require a higher breathing rate
 Have a lower compliance

GENERAL CALIBRATION PROCEEDURES FOR
VOLUME/PRESSURE VENTILATORS
◦ Ensure annual manufacturer’s calibration
◦ Ensure equipment is designed to accurately measure the
delivery from the unit under test
 High flow adult
 Low flow pediatric
 High frequency
◦ Obtain ventilator information
 What settings must the ventilator be placed in to measure
volumes and flows
 Test device must be set accordingly to ensure proper
measurements
 Failure to do so may result in the maladjustment of the
ventilator

Ventilator Measurement Standards
◦ Flow and volume measurements are affected by
 Type of gas (air, oxygen or mixed)
 Temperature
 Pressure
 Water vapor
◦ BTPS – Body Temperature Pressure Saturated
 Body temperature – 37° C
 Pressure – ambient barometric pressure
 Saturated – water vapor at 100% relative humidity
 Usually used when the flow of gases has been
changed to patient conditions (exhalation)
◦ STPD – Standard Temperature Pressure Dry
 Standard temperature – usually 0 or 21° C
 Pressure – ambient barometric pressure
 Dry – water vapor at 0% relative humidity
 Usually used when the flow of gases has been
changed to standard conditions (wall
supply/inhalation)