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 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 diffusion  Patient requires higher pO 2 (partial pressure of oxygen) gradient to force O 2 to diffuse  Allows the P aw to be reduced but keeps pO 2 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)