Without reference, identify principles about volume/pressure and high frequency ventilators with at...

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

Volume/Pressure and High Frequency Ventilators

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 oVolume, 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

oPressure, 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 resistanceo 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 Started when the patient attempts to take a breath o Once initiated the ventilator delivers a controlled breath o Breath is known as an "assisted" breath o The sensitivity or trigger sensitivity parameter must be

set to the patient's efforts


Timed cycled o Inspiration begins after a predetermined time has passed o Timer is independent of the patient o Controlled by the "breaths/min" setting o Classified as a "strict controller" if no assist mechanism is

used o Often used as a backup to patient cycling


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 diffusionPatient requires higher pO2 (partial pressure of oxygen) gradient to force

O2 to diffuse Allows the Paw to be reduced but keeps pO2 high

InfantsRequire 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)


Without reference, identify principles about volume/pressure and high frequency ventilators with at...

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