Volume/Pressure and High Frequency Ventilators

1. Without reference, identify principles about volume/pressure and high frequency ventilators with at least 70 percent accuracy.

2. Volume/Pressure and High Frequency Ventilators • Purpose of Volume/Pressure Ventilators • Device used to move gas into the lungs • Required when • Acute respiratory failure • No absolute rule

3. 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

4. Volume/Pressure and High Frequency Ventilators • 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

5. Volume/Pressure and High Frequency Ventilators • 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 • Use a balloon-like cuff which seals against the walls of the trachea • All gas flow is through the intubation tube

6. Volume/Pressure and High Frequency Ventilators • Limiting Devices - Required to prevent barotraumas (lung damage) • Pressure limiter • Pressure developed by the drive mechanism may be high enough to injure the lungs • Methods • Vent excess pressure • End the inspiration completely

7. Volume/Pressure and High Frequency Ventilators • 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

8. Volume/Pressure and High Frequency Ventilators • 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 • Inspiration is ended when a predetermined pressure is reached • Volume, flow rate, and inspiratory time may all vary from one inspiration to another

9. Volume/Pressure and High Frequency Ventilators • Flow cycled ventilators • Inspiration is ended when the flow of gas into the patient falls below a specific point • Volume, pressure, and inspiratory time may vary from one inspiration to another • Volume cycled ventilators • Inspiration is ended when a predetermined volume of gas has been delivered to the patient • Pressure, flow rate, and inspiratory time may vary from one inspiration to another

10. Volume/Pressure and High Frequency Ventilators • Time cycled ventilators • Inspiration is ended after a predetermined time • 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 • It is a period of time at the end of an inspiration that the lungs are kept inflated • Also known as inspiratory hold, inspiratory pause, or inspiratory plateau

11. Volume/Pressure and High Frequency Ventilators • Expiratory phase • Allows the lungs to empty • Normally not restricted by the ventilator • Adjuncts of the expiratory phase • Expiratory resistance • Application of mechanical resistance to the exhalation port of the breathing circuit • Increases the mean airway pressure

12. Volume/Pressure and High Frequency Ventilators • 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

13. Volume/Pressure and High Frequency Ventilators • 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

14. Volume/Pressure and High Frequency Ventilators • 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 • 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

15. Volume/Pressure and High Frequency Ventilators • 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 • Often used as a backup to patient cycling

16. Volume/Pressure and High Frequency Ventilators • 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

17. Volume/Pressure and High Frequency Ventilators • 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 • A mandatory SIMV breath will be given • At the beginning of the next spontaneous phase

18. Volume/Pressure and High Frequency Ventilators • 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

19. Volume/Pressure and High Frequency Ventilators • 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

20. Volume/Pressure and High Frequency Ventilators • 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)

21. Volume/Pressure and High Frequency Ventilators • 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)