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2  High Frequency Ventilation (HFV)  High Frequency Oscillatory Ventilation (HFOV) and how it works  When do we use HFOV  Basic Parameters for HFOV  How HFOV prevents Ventilator Induced Lung Injury (VILI) Overview

3 High Frequency Ventilation Provides augmented gas distribution By means of numerous gas transport mechanisms.  Convection, transit time, direct ventilation  Pendalluft effect  Taylor dispersion  Asymmetric velocity  Cardiogenic Mixing  Molecular diffusion  Collateral Ventilation

4 Convection, Transit Time and Direct Ventilation Convection  is the transport of air flow at a constant equal velocity that is parabolic in shape. Transit Time:  Airflow to the alveoli will vary in proportion to the length of the Bronchial airways. Direct Ventilation:  Results from bulk air flow to alveoli that have a much shorter transit time.

5 Taylor Dispersion Pendalluft Effect At the end of expiration: Alveoli with short time constants (fast alveoli units) are empty. Alveoli with longer time constants (slow alveoli units) are still emptying Asynchronous filling: Gases will move from slow units to fast units because of pressure gradients between the alveoli. Asynchronous Filling The relationship between:  Axial velocity profile (Turbulence)  the diffusion of gases in motion  and the branching network of the lungs.

6 AsymmetryCardiogenic Mixing Airflow moving through the airways moves in a u-shape formation. At the center of the lumen air will move at a faster velocity, than air that is closest to the wall. Asymmetry Occurs with rapid respiratory cycles. Gases (O2) at the center of the lumen will advance further into the lungs as gases (CO2) along the wall of the airway moves out towards the mouth. As the heart beats the heart provides additional peripheral mixing by exerting pressure against the lungs during contraction of the heart. This pressure promotes the movement of gas flow through the neighboring parenchymal regions.

7 Collateral Ventilation Molecular Diffusion Maintaining a constant distending pressure with HFV within the lungs along with movement of gas molecules promotes gas diffusion across the alveolar membrane, at a faster rate. Collateral ventilation increases with HFV due to connections between the alveoli  (Pores of Kohn)


9 How does it work?  Small tidal volumes at high frequency are generated by low amplitude pressure oscillations. These tidal volumes that are approximately equal to dead space.  High mean airway pressures (PEEP) provides distending pressure.  HFOV can provide 5-15 Hz equal to (900 breaths/min. What is HFOV  HFOV has all of the elements of high frequency ventilation discussed previously.  Also provides a bias oscillatory gas flow used to generates positive and negative pressure fluctuations referred to as amplitudes or (Delta-P) Amplitude Oscillation/Frequency Hz MAP/PEEP



12 External Air/O2 Blender 1. Provides blended air/O2 and cooling to the oscillator External Humidifier 1. Attaches and functions with the patient’s circuit 2. Capable of flows up to 40 LPM Pneumatic Logic and Control System Comprised of 4 pneumonic controls 1. Bias flow 2. Mean Pressure adjustments 3. Mean pressure limit control 4. Patient circuit calibration adjustment Patient Circuit Provides: 1. Bias flow/pressure 2. Pressurized oscillations 3. Pressure limiting Oscillator Subsystem Uses an 1.electronic control circuit called the square wave form driver 2. Forward and backward linear motion provides inspiratory and expiratory gas flow. 3. Provides frequent small VT in HZ Pressure Monitoring System 1. Safety and alarms rely on this system 2. The PMS senses pressures within the patient’s circuit through the tubing that runs from the y-coupler Electronic Power Supply Monitors: 1. Alarms 2. Pressures 3. Function of the oscillator HFOV: 3100A

13 3100 A 3100A Interface: 1.Bias flow knob 2.Mean Pressure adjustment 3.Mean Pressure Limit 4.Power 5.% Inspiratory Time 6.Frequency 7.Start/Stop 8.Mean Airway Pressure 9.Set Max Paw 10.Set Min Paw 11.Paw >50 cm H2O 12.Paw <20 cm H2O 13.Power failure Button 14.Reset 15a Battery Low 15b Source Gas Low 16. Oscillator Overheated 17. Oscillator stopped 18. 45 second Silence 4 2 3 5 6 1 7 8 9 10 15b 15a 16 17 13-14 11 12 18

14 Amplitude : Determines the volume of gas generated by each frequency wave Oscillation/ Frequency (Hz) Frequency = The Rate  15 Hz =900 BPM for neonates  12-14 Hz =600 BPM for termed infants  8 Hz =480 BPM for children 6-10 kg  6 Hz =360 BPM for children above 10 kg Amplitudes  2.5 for  3.0 for  4.0 for  5.0 for  6.0 for  7.0 for Weight: kg/mg <2.0 kg. <3.0 kg <2.5-4.0 kg 4.0-5.0 kg < 10 kg >20 kg IT% Inspiratory Time Percentage  33% IT = 22 milliseconds a 15 Hz I:E: For HFOV I:E also determines the time for movement of the piston to generate another oscillatory breath.  Initial I:E of 1:2 for 3-15 Hz at 33% IT MAP/PEEP: Maintains constant distending pressure in the airway  15-18 cmH2O Adjustable Parameters


16 Pneumopertioneum Sub cu-emphysema Pneumopercardium Pneumomediastinum Pneumothorax ARDS

17 Potential Advantages of HFOV are 1. Uniform inflation of the lung fields 2. Improves gas exchange 3. Improves lung mechanics 4. Enables stable lung inflation o Allows recruitment of alveolar space o Reduces the risk of volutrauma o Reduces risk of high peak airway pressure (PIP) o Reduces the risk of airway stretching o Improves V/Q matching 5. Reduces air leak 6. Decreases the amount of inflammatory mediators and alveolar edema 7. Prevents the development of hyaline membrane disease (HMD)

18 During CMV, there are swings between the zones of injury from inspiration to expiration. During HFOV, the entire cycle operates in the “safe window” and avoids the injury zones. CMV HFOV INJURY CMV VS HFOV

19 Volume Pressure Zone of Overdistention Safe window Zone of Derecruitment and atelectasis Goal is to avoid injury zones and operate in the safe window HFOV is used to prevent Ventilator Induced Lung Injury

20 Indications: When traditional ventilation fails Airleak syndromes For patients with severely low lung compliance Refractory hypoxemia Contraindications: ICP obstructive lung disease increased airway resistance (small endotracheal tube) asthma secretions increased physiological dead space

21 Work Citations Page: Alves, Amanda. “High Frequency Oscillatory Ventilation HFOV; a new strategy in the Treatment of patients with Acute Respiratory Distress Syndrome and low lung compliance.” CIMC 2000. Web 13 August 2014. Birch, Pita. “Newborn Services Clinical Guideline High Frequency Oscillatory Ventilation.” Web. 14 August 2014. CareFusion; “3100A High frequency oscillatory ventilation; Operator’s manual.” CareFusion Corporation. 222745 Savi Ranch Parkway Yorba Linda, CA 92887-4668. Web 18 August 2014 Haines, Mike. “Mechanical Ventilation: High Frequency Ventilation.” Respiratory Therapy Files. Web. 8 August 2014. Jeng, Mei-Jy. Lee, Chen, Soong. “Neonatal air leak syndrome and the role of high-frequency ventilation.” Sci Verse Science Direct Journal of the Chinese Medical Association 75 (2012) 551e559 Web. 8 August 2014. Prost, Allen. “High Frequency Oscillation Ventillation.avi.” 2011. Web 24 Aug. 2014. Slee-Wijffels1, Fieke YAM. RM van der Vaart, Twisk, Markhorst, Plötz5 “High-frequency oscillatory ventilation in children: a single-center experience of 53 cases, pp. R274” Open Access. 16 Web August 2104. Slee-Wijffels1, Fieke YAM. RM van der Vaart, Twisk, Markhorst, Plötz5 “High-frequency oscillatory ventilation in children: a single-center experience of 53 cases, pp. R274” Open Access. 16 Web August 2104.


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