HFOV high frequency Oscillatory Ventilation Becky Varela & Jamie Wood

Overview 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)

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

Convection, Transit Time and Direct Ventilation 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.

Asynchronous Filling 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. The relationship between: Axial velocity profile (Turbulence) the diffusion of gases in motion and the branching network of the lungs.

Asymmetry Cardiogenic 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.

Collateral Ventilation Molecular Diffusion Collateral Ventilation 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)

Oscillation/Frequency Hz 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) Oscillation/Frequency Hz Amplitude MAP/PEEP

HFOV: 3100A Oscillator Subsystem Uses an External Air/O2 Blender 1. Provides blended air/O2 and cooling to the oscillator 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 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 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 Patient Circuit Provides: 1. Bias flow/pressure 2. Pressurized oscillations 3. Pressure limiting

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

Adjustable Parameters 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 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 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

Pulmonary Diseases and Disorders treated with HFOV https://www.youtube.com/watch?v=dHuXtoODHuA

Pneumopertioneum Sub cu-emphysema Pneumopercardium Pneumomediastinum Pneumothorax ARDS

Potential Advantages of HFOV are 1 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)

CMV VS HFOV 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. INJURY HFOV CMV INJURY

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

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

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. http://www.adhb.govt.nz/newborn/guidelines/respiratory/hfov/hfov.htm 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. http://www.respiratorytherapyfiles.net 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. http://homepage.vghtpe.gov.tw/~jcma/75/11/551.pdf Prost, Allen. “High Frequency Oscillation Ventillation.avi.” Youtube.com. 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. http://www.biomedcentral.com/content/pdf/cc3520.pdf