Richard Ditsch, BS, RRT, RCVT Clinical Education Specialist VIASYS Healthcare Viasys HealthCare

Objectives: Following review of this self-study program for ventilating a neonate on high-frequency oscillatory ventilation the reader will be able to answer the list of questions at the end of this self-study program.

High Frequency Oscillatory Ventilation Definition: The delivery of small tidal volumes (<2-3cc) at high rates (>150 BPM).

Why HFOV ? Safe use of the 3100A high frequency ventilator is to prevent the incidence of chronic lung injury. Conventional mechanical ventilators (CMV), positive pressure ventilators has side effects when used to ventilate infants.1, 2, 3

Why use HFOV? The 3100A ventilator uses smaller tidal volumes than conventional ventilation. The 3100A keeps the alveolar sacs open at a constant mean airway pressure. This will reduce the incidence of alveolar over-inflation during the inspiratory breath and reduce alveolar collapse during the expiratory phase of ventilation.

Why use HFOV? Maintaining a constant mean airway pressure prevents the incidence of over-inflation and alveolar collapse which produces lung injury. This is know as lung protection strategy.5,6

Optimized Lung Volume Strategy: Decrease Tidal Volumes to less or equal than dead space and increase frequency. Benefits: - enhanced gas exchange due to combined gas transport mechanisms - no excessive volume swings - reduced regional over-inflation and stretching - reduced Volutrauma

How does HFOV work? HFOV provides a small tidal volume which is usually equal to or less than anatomical dead space. HFOV uses very fast respiratory rates, usually 600 to 900 breaths per minute (bpm) (10 – 15Hz) for neonates. The frequency is expressed in Hertz’s (Hz). One Hz equals 60 bpm, 15 Hz equals 900 bpm.

Pulmonary Injury Sequence of the neonatal patient: Absence of Surfactant Atelactasis Tidal Breathing High Distending Pressures Airway Stretch / Distortion Cellular Membrane Disruption Edema / Hyaline Membrane Formation Higher FIO2 , Volumes, Pressures Volutrauma, Barotrauma, Biotrauma PIE, BPD

Optimized Lung Volume “Safe Window” Over distension Edema fluid accumulation Surfactant degradation High oxygen exposure Mechanical disruption Derecruitment, Atelectasis Repeated closure / re-expansion Stimulation inflammatory response Inhibition surfactant Local hypoxemia Compensatory overexpansion Zone of Over distention Injury “Safe” Window Volume Zone of Derecruitment and Atelectasis Injury Pressure

Optimized Lung Volume Strategy: CT Scan : ARDS pig model 30 kg Mean Airway pressure 5 cm H2O

Optimized Lung Volume Strategy: CT Scan : ARDS pig model 30 kg Mean Airway pressure 25 cm H2O

Optimized Lung Volume Strategy: CT Scan : ARDS pig model 30 kg Mean Airway Pressure 40 cm H2O

CT 2 CT 1 CT 3 Paw = CDP CDP= FRC Continuous Distending Pressure

Comparison of HFOV & Conventional Ventilators Differences CMV HFOV Rates 0-150 180 – 900 Tidal Volume 4-20ml/kg 0.1-0.3ml/kg Alveolar pressure 0->50cmH2O 0.1-5cmH2O End Exp Volume Low Normalized Gas Flow Low High Exhalation Phase Passive Active

Thinking Outside of the Box Comparison of CMV to HFV ? How could it possibly work ? Gas Exchange Mechanisms Patient Care ? Focus on assessing the patient and treating the underlying lung process, rather than treating ABG report ? Learning to rely on our skills as a clinician WILL EVERYONE BE “HAPPY”!!

CMV side effects Decreased cardiac output: with inspiratory pressures being higher than normal, this increase in pressure can reduce venous return and decrease cardiac output. Decrease urine output, as cardiac output falls, the kidneys will attempt to retain fluid. With all ventilators there is a risk of ventilator associated pneumonia.

CMV side effects Risk of tracheal and lung damage if inspired gas is not humidified.4 Lung trauma due to high inspiratory airway pressures. Volutrauma is associated to too large of inspiratory volumes without improvement in alveolar gas exchange. Increase incidence of intraventricular hemorrhage.7

Endotracheal Tube The endotracheal tube acts as a filter to the pressure wave form during high frequency oscillatory ventilation, attenuating (dampening) the pressure as great as 90% with a 2.5 I.D. ET tube. The larger the tube, less attenuation.4

Ventilation

Paw is created by a continuous bias flow of gas past the resistance (inflation) of the balloon on the mean airway pressure control valve.

Alveolar ventilation during CMV is defined as: F x Vt Alveolar Ventilation during HFV is defined as: F x Vt 2 Therefore, changes in volume delivery (as a function of Delta-P, Freq., or % Insp. Time) have the most significant affect on CO2 elimination

Power Settings Start with a power setting of 2.0 to generate the amplitude pressure, increase the power setting to increase amplitude pressure to obtain chest wiggle. DO NOT INCREASE THE POWER SETTING TO EXCEED CHEST WIGGLE BELOW THE UMBILICUS. TOO MUCH POWER CAN DECREASE PaCO2.

Primary control of CO2 is by the stroke volume produced by the Power Setting.

The % Inspiratory Time also controls the time for movement of the piston, and therefore can assist with CO2 elimination. Increasing % I-Time is used in primarily in larger pediatric patients. Increasing % Inspiratory Time will also affect lung recruitment by increasing delivered Paw. NEVER increase the I Time% with a setting of 10 - 15 Hertz Frequency, may increase the risk of inadvertent gas trapping.

Inspiratory / Expiratory Ratio: I/E Ratio adjustable with Inspiratory time control Inspiratory time = Forward movement piston Expiratory time = Backward movement piston Backward movement piston = active exhalation ! Recommended Insp. time = 33% (prevents airtrapping) + 30% -- 70% Inspiratory time adjustable: 30% - 50%

3100A Operational Characteristics Blended medical air and oxygen is provided to the ventilator circuit, 40-60 psig. Medical air is connected to the back of the ventilator to keep the piston cool, 40-60 psig, 15 LPM max consumption Inspired gas is humidified, recommend to keep the inspiratory temperature at 36 – 37 degrees Celsius. Bias flow us set to maintain mean airway pressure within the circuit.

3100A Operational Characteristics Mean Airway Pressure adjustment from 3 cmH20 – 45cmH20. Bias flow dependent. Oscillatory pressure ( delta pressure ) or amplitude pressure of > 90 cmH20 max amplitude pressure. Frequency: 3 – 15 Hz (180 – 900 BPM) % inspiratory time: 30 – 50% Pressure Monitors: Mean and Oscillatory Pressure, delta pressure.

3100A Operational Characteristics Piston Centering Adjust: Applies electrical counterforce to piston coil to maintain piston centering. Pressure Measurements: Range +/- 130 cmH20 Accuracy +/- 2% of reading or +/- 2cmH2O, whichever is greater.

3100A Operational Characteristics Indicators: Mean airway pressure Oscillatory amplitude pressure % inspiratory time Frequency (Hz) Piston Position and Displacement Bias Flow, continuous flow to the circuit.

3100A Operational Characteristics Alarms: Safety dump valve will open when: Mean airway pressure > 50 cmH20 Mean airway pressure < 20% of Set Max Mean airway pressure. Warning: Above “Set Max Mean airway pressure” Below “Set Min Mean airway pressure” Power Failure Oscillatory Stopped

3100A Operational Characteristics Caution: L.E.D. displays Oscillator Overheat Battery Low, 9 volt battery Source Gas low pressure Electrical connections: Always connect electrical outlet to emergency power outlet.

3100A Operational Characteristics Standard single lumen endotracheal tube is to be used with the oscillator. Closed suction systems works well to maintain mean airway pressure when suctioning. If you use an open suction system make sure the manual resuscitator is used to reduce the incidence of loss of lung volume known as de-recruitment.

Red Line Balloon Control - Balloon Deflation (valve opening) - Main power failure - Map > 50 cm H2O - Map <20% max. CDP alarm set

Oscillator Section Centering Display - Frequency (3-15 Hz) Controls - Frequency (3-15 Hz) - I/E Ratio (30-50%) - D pressure (0 - > 90 cm H2O) - Start/Stop Button Centering Display D pressure

Bias Flow CDP Control Balloon

Patient Preparation Obtain a chest x-ray as your baseline film prior to starting the oscillatory. Hemodynamic status stabilized: (initial goal to maintain MAP equal to gestational age). Crystalloid fluids Colloid administration Vasopressors

Patient Preparation The Infant bed should be firm, do not use a water bed or lambs wool under the thorax of the infant if all possible, the goal is to ensure that the amplitude pressures wiggles the chest rather than the mattress. If the infant is on a radiant bed warmer, place the infant with his/her head at the foot position and the head at the control position of the mattress. This will provide ease of oscillator circuit connection.

Patient Preparation Thoroughly suction the infant prior to application of the oscillator ventilator. The need to suction will decrease once the patient is placed on the oscillator. Make sure that the humidifier is set to provide good humidity to the breathing circuit. 35 – 37 degrees Celsius. If using closed suction have the system setup prior to HFOV application and connected to the circuit.

Patient Application Closed suction systems: Closed suction will ensure that you will not loose the mean airway pressure, i.e. lung recruitment while suctioning. You do not need to stop the oscillator when you suction the patient. Always make sure that the suction valve is turned off when not in use.

Patient Preparation Provide continuous monitoring of the following: Pulse oximetery (SaO2) Mean arterial pressure (MAP) Heart Rate (HR) Color Trancutaneous Carbon Dioxide Monitoring (TCM)

Patient Application Make sure that the endotracheal tube does not have tension due to the HFOV breathing circuit. Assess chest wiggle as amplitude pressure is increased. Observe chest wiggle to a level down to the umbilicus. Monitor trancutaneous CO2 levels to desired levels, 38-48mmHg. Observe SaO2 to maintain a level of 88 to 93%. Make sure the FiO2 is at 1.0 when starting.

Patient Monitoring post HFOV Monitor SaO2, maintain SaO2 levels of 88 -93% as your monitor for oxygenation. Monitor chest wiggle, chest wiggle is the only immediate monitor for ventilation. If you have transcutaneous CO2 monitor use to monitor CO2 levels. Only run TCM CO2 temperature at 39 degrees C. Monitor mean arterial pressure to ensure that cardiac output is maintained. YOU MUST WAIT ONE HOUR BEFORE THE FIRST ARTERIAL BLOOD GAS.

Patient Assessment You will have to PAUSE the oscillator when you need to listen to Heart Sounds Bowel Sounds Breath Sounds ONLY STOP THE VENTILATOR FOR 60 SECONDS OR LESS FOR ASSESSMENT.

Arterial Blood Gases Hypoxia and Hypercarbia: - Low PaO2, increase mean airway pressure by no more that 2 cmH20, monitor SaO2 to observe an increase. Monitor mean arterial pressure. - High PaCO2, increase amplitude pressure to increase chest wiggle, increase power setting by no more than 0.5 power setting or no more than 5 cmH20. WAIT ONE HOUR FOR NEXT ABG.

Arterial Blood Gases Hperoxia or Hypocarbia High PaO2, decrease FiO2 by no more that 5% every 30-60 minutes, wean slowly. If the SaO2 decreases to below 88%, increase FiO2 back to previous FiO2. Low PaCO2, Increase frequency if not on 15 Hz. If on 10 Hz, increase frequency to 12 Hz. Decrease amplitude pressure by no more that 5 cmH20 pressure, decrease power setting to decrease amplitude pressure. WAIT ONE HOUR BEFORE YOU OBTAIN THE NEXT ARTERIAL BLOOD GAS.

Patient Monitoring Obtain first Chest X-Ray at one hour post HFOV set-up. Goal to have lung inflation via monitoring rib inflation levels, 8th – 9th inter-costal levels is the goal for safe lung inflation.

Ventilation The amplitude shown on the LED read out is measured within the circuit, not in the airway. HFOV is considered a VERY GENTLE form of ventilation.

Clinical Tips for Neonatal Strategies The oscillator is used for hypoplasia syndrome to protect the abnormally developed, small lungs and maintain ventilation. A transient improvement may be seen and then failure, which may be due to an insufficient amount of lung tissue or the onset of PPHN. HFOV as a rescue tool may not be effective in cases of hypoplasia. Early management with HFOV, to prevent barotrauma and acidosis, may improve outcomes.

Care of the Patient May require additional fluids or vasopressors to support hemodynamics. May require sedation or paralytics based on the underlying disease process. Most RDS infants were found to require less sedation and fluids as compared to CMV with “Early Application”.

Clinical Tips for Neonatal Strategies Guideline is for initial starting point. If O2 saturation does not improve within 5-10 min., increase the Paw until the saturation is 88-93%. Increase Paw until you see a rise in CVP or signs of decreased systemic blood flow Obtain a Chest X-Ray for observation of lung expansion to 8-9 posterior ribs or decreased opacification

Clinical Tips for Neonatal Strategies Once oxygenation improves, maintain the Paw and monitor the infant for changes in perfusion. Wean FiO2 to 60% or less, re-check x-ray if diaphragm expansion is 9 rib level or more, decrease the Paw 1 cmH2O if diaphragm expansion is 8 to 8-1/2 rib level, continue to wean FiO2 and monitor hemodynamics

Neonatal Strategies Airleak (Premature Infant less than 1000 gms) Pulmonary Interstitial Emphysema (PIE) Paw set at 1 cmH2O less or equal to CMV’s Paw Frequency 15 Hz Power of 2.0 and then adjust for minimal CWF Gross Airleak Paw set equal to or 1cmH2O higher than CMV’s Paw Frequency 15 HZ Power of 2.0 and then adjust for adequate CWF

Clinical Tips for Neonatal Strategies Use the 3100A to treat PIE the moment it is suspected or evidence of PIE on CXR is seen. The earlier application has better outcomes than following severe bilateral involvement. DO NOT aggressively increase Paw. This results in further worsening of PIE and trapped gas. Accept saturations of 87 - 90% initially and use higher FiO2’s and PaCO2’s until evidence of PIE resolution is seen.

Neonatal Strategies Airleak (Term or Near Term Infant) Gross Airleak with poor inflation Paw initiated at equal to or 1-2 cmH2O > than CMV’s Paw Frequency at 10 Hz Power of 2.5 and then adjust for adequate CWF Gross Airleak with adequate inflation Paw set equal to or 1cmH2O < than CMV’s Paw

Patient weaning Decrease FiO2 slowly, no more than 5% decease per change, decrease FiO2 to less than 40 – 60 %. Wean mean airway pressure, after FiO2 is less than 60% or less. Decrease mean airway pressure by 1cmH2O. Do not wean mean airway pressure more frequently than q 4-6 hours.

Amplitude weaning Decrease amplitude pressure to maintain PCO2 at desired levels. Decrease power setting to decrease amplitude pressure. Do not wean amplitude pressure by more than 3-5 cmH2O per adjustment. Monitor chest wiggle, SaO2 and TCM levels.

WEANING Wean FiO2 for arterial saturation of 88 - 93% Once FiO2 is .40 - .60 or less, may decrease MAP in increments of 1 cm H2O Delta P is weaned by increments of 5 cm H2O for desired PaCO2 Once optimal frequency is found, leave the frequency throughout the run. However you may increase the frequency to raise the PaCO2

Conversion from HFOV to CMV or to CPAP FiO2 is less than .40 MAP requirement is between 10 and 15 or less Delta P is less than 30 cmH2O Patient plateaus for several days with a good spontaneous respiratory effort Tolerates suctioning or disconnect

HFOV Summary Despite improvements in respiratory care, ventilator-induced lung injury remains and important cause of morbidity and mortality in neonates who require assisted ventilation. Animal data and human data demonstrate that HFOV can be used successfully to reduce lung injury.

HFOV Summary HFOV is dependent on optimizing functional residual capacity and avoiding lung over inflation. Using HFOV to promote lung recruitment it effectively reduces the occurrence of chronic lung injury. Clinicians need to monitor the patients response to oscillation therapy to ensure improvement in health outcome.

Clinical References 1. Froese AB: Role of lung volume in lung injury: HFO in the atelectasis prone lung. Acta Anaesthesiol Scand 90:126-130, 1989 2. DreyfussD, Saumon G: Ventilator-induced lung injury: Lessons from experimental studies. Am J Respir Crit Care Med 157: 294-323, 1998 3. Slutsky AS: Lung injury caused by mechanical ventilation. Chest 116(Suppl):S9-S15, 1999 4. Gerstmann DR, Fouke JM Winter DC, et al: Proximal, tracheal and alveolar pressures during high- frequency oscillatory ventilation in a normal rabbit model. Pediatr Res 28:367-373 1990

Clinical References 5. McDougall PN, Loughnan PM, Campbell NT: High-frequency oscillation in newborn infants with respiratory failure. J Paedr Child Health 31:292-296, 1996 6. Rimensberger PC, Beghetti M, Hanquinet S, et al: First intention high-frequency oscillation with early lung volume optimization improves pulmonary outcome in very low birth weight infants with respiratory distress syndrome. Pediatrics 105: 1202-1208, 2000

Clinical References 7. Clark RH, Gerstmann DR, Null DM et al: Prospective randomized comparison of high-frequency oscillatory and conventional ventilation in respiratory distress syndrome. Pediatrics 89:5-12 1992

Study Questions 1. Why is HFOV used today? 2. What causes lung injury when conventional mechanical ventilators are used? 3. What phase of expiration does the oscillator use?

Study Questions 4. What is the range of SaO2 that you want to maintain when setting up the HFOV? 5. How long do you have to wait for arterial blood gas analysis after changes are made to the oscillator?

Study Questions 6. Optimal lung expansion is to maintain lung inflation to what rib level? 7. What do you have to do to listen to heart sounds with the HFOV? What steps should be followed before you place a patient on the oscillator?

Study Questions 8. What parameter do you wean first when the SaO2 is greater than 95%? 9. If the patients PaCO2 is high you should increase what parameter for a 1000 Gm infant? 10. How fast will the oscillator cycle?

Study Questions 11. Why should closed suction systems be used for high frequency oscillator patients? 12. True or False: All patients are to be sedated and paralyzed throughout HFOV? 13. To determine adequate amplitude you need to assess chest wiggle to what anatomical location?