Management Strategies with High Frequency Oscillatory Ventilation (HFOV) in Neonates Using the SensorMedics 3100A High Frequency Oscillatory Ventilator
Jonathan M. Klein, MD
Peer Review Status: Internally Peer Reviewed
SensorMedics 3100A Oscillatory Ventilator
The 3100A is a true high frequency oscillator with a diaphragmatically sealed piston driver. It is theoretically capable of ventilating patients up to 30 kg. Tidal volume typically delivered ≈ 1.5-3.0 cc/kg (< dead space). The 3100A is an extremely efficient ventilator secondary to an active expiratory phase, but it is not capable of delivering sigh breaths for alveolar recruitment.
Set initially at 10 Hz (600 BPM) for term infants and 15 Hz (900 BPM) for premature infants (< 2.5 kg). For children between 6-10 kg, use 8 Hz, and for children > 10 kg, use 6 Hz for an initial setting.
INSPIRATORY TIME (I.T.)
Set initially at 33% (e.g. 22 milliseconds at 15 Hz, 41 milliseconds at 8 Hz, 55 milliseconds at 6 Hz).
1) Warning - The percent of I.T. should never be increased because it will lead to air trapping and fulminant barotrauma. Total I.T. should only be increased by decreasing frequency, thus leaving the I:E ratio constant. I.T. can be decreased to 30% to heal air-leaks.
2) I:E ratio: ≈ 1:2 for 3-15 Hz at 33% I.T.
A rough representation of the volume of gas generated by each high frequency wave. Range (1.0 - 10.0). Maximum true volume of gas generated by the piston is 365 cc. Maximum amplitude or volume delivered is highly variable and depends on the following factors: circuit tubing (compliance, length and diameter), humidifier (resistance and compliance - water level), ET tube diameter and length (FLOWis directly proportional to r4/l, where r = radius of airway and l = length of airway), the patient's airways and compliance.
1) Set the POWER initially at 2.5 if wt <2.0 kg, 3.0 if wt < 2.5 kg, 4.0 if wt 2.5 - 4.0 kg, 5.0 if wt 4.0 - 5.0 kg, 6.0 if wt < 10 kg, 7.0 if wt > 20 kg.
- Check ABG's every 15-20 min until PaCO2≈ 40-60, i.e., titrate POWER setting based on PaCO2 desired.
- Chest wall needs to be vibrating. If not vibrating, increase power.
- Many HFOV centers have you order amplitude or delta P (ƒ¢P) to regulate ventilation instead of power. We have decided that the Power setting is a more reliable way of adjusting this ventilator and thus we order changes in power in order to regulate ventilation.
2) Alveolar ventilation is directly proportional toPOWER, so the level ofPaCO2 is inversely proportional to the power.
3) During HFOV, alveolar ventilation (Ve) ≈ (TV)2f as compared to CMV where Ve ≈ TV(R). Thus we primarily adjust the power (amplitude) to change tidal volume in order to manipulate ventilation.
4) Management of ABG's (Ventilation - Ve):
a) Change POWER by 0.2-0.3 to change CO2± 2-4 mm Hg
b) Change POWER by 0.4-0.7 to change CO2± 5-9 mm Hg
c) Change POWER by 0.8-1.0 to change CO2± 10-15 mm Hg
5)Warning - It is extremely important to normalize PaCO2 rapidly by weaning Power in order to avoid volutrauma from excessive tidal volumes.Check ABG's frequently (Q15-20 min) and decrease POWER accordingly until PaCO2 > 35. A PaCO2< 35 correlates with an increased risk of pneumothorax. Thus to minimize the risk of volutrauma, it is important to use the least amount of TV (POWER or AMPLITUDE) possible to achieve ventilation.
6) Hypercarbia - If PaCO2 still remains elevated at high POWER setting (>8.0), decrease FREQUENCY by 2 Hz every 15-20 min until maximum tidal volume is reached (3-4 Hz at a POWER of 10.0). The lower frequency leads to a longer I.T. leading to a larger tidal volume of gas being displaced towards the infant. This increased TV leads to improved alveolar ventilation (HFOV, Ve ≈ (TV)2f).
7) Manual Ventilation: Hand bagging while on the SensorMedics Ventilator should be avoided secondary to the risk of barotrauma due to over distention. Suctioning should be performed using just the ventilator breaths alone (an inline suctioning adapter would be best). If bagging has to be done, the PIP while bagging should not exceed 8-10 cm above the MAP and a PEEP of 6-8 cm should be maintained as tolerated.
Oxygenation on HFOV is directly proportional to MAP, which is similar to CMV, however with the SensorMedics HFOV the MAP is generated by PEEP. Thus during HFOV: MAP = PEEP.
1. Initial MAP Settings:
a) Neonates - Initial MAP should be 2-4 cm above the MAP on CMV.
b) Infants/Children - Initial MAP should be 4-8 cm above the MAP on CMV.
c) If starting immediately on HFOV - use a MAP of ≈ 8-10 cm in neonates and 15-18 cm in infants/children.
2. Management of ABG's (Oxygenation is directly proportional to MAP):
a) If not oxygenating adequately at initial MAP (12-18 cm), obtain CXR to assess lung volume. If lung is not hyper-inflated (flattened diaphragm) or is below optimal lung volume around 9-10 ribs then increase MAP by 2-4 cm every 20-30 min until adequate oxygenation is achieved or lung starts to become over-inflated (e.g. FiO2 0.6-0.7 increase by 2-4 cm, FiO2 1.0 increase by 4-8 cm).
b) Maximum potential MAP = 40-45 cm
c) Warning - If oxygenating adequately, but the lung is hyper-inflated immediately decrease the MAP by 1-2 cm every 2-4 h until lung volumes return to normal. If the lung is allowed to remain hyper-inflated for prolonged periods of time the risk of barotrauma increases dramatically.
d) If not oxygenating with lung becoming hyper-inflated, you can decrease frequency as a way to increase I.T. while keeping I:E ratio constant.
The SensorMedics HFOV is usually used for premature infants, term infants or young children with respiratory failure not responsive to CMV.
TERM INFANT WITH SEVERE RESPIRATORY FAILURE (PPHN, MAS, GBS pneumonia, RDS)
- Start at a frequency of 10 Hz and a Power of 3.0 to 5.0. Initial MAP 4 cm above MAP while on CMV. Check CXR 2 hrs after converting to HFOV, then adjust MAP to achieve optimal lung volume (9-10 ribs expanded).
- If not oxygenating, increase MAP by 2 cm every hour until oxygenation improves. Adjust Power to keep PaCO2 45-55.
Pneumothorax or PIE
- The goal is to minimize both tidal volumes and peak pressures generated by any given TV. Practice permissive hypercarbia and accept high PaCO2's to minimize the TV.
- Tolerate transiently increased FiO2 requirements (0.6 - 1.0) in order to keep MAP at a minimum.
- Use a FREQUENCY of 12-15 Hz in order to minimize both total I.T. and TV in order to heal the airleak.
- Decrease I.T. to 30%.
The goal is to minimize volutrauma, barotrauma and oxygen toxicity. Thus use the minimum POWER possible at the appropriate FREQUENCY in order to keep PaCO2 adequate (e.g. 55-65 mm Hg). Increase MAP as high as necessary to keep FiO2 < 1.0. Also decrease frequency to increase I.T. to improve oxygenation.
Give surfactant replacement therapy using manual bagging. Start with frequency of 15 Hz, I.T. of 33%. Use MAP of 8-10 cm or 2 cm above MAP on CMV. Wean FiO2 until <0.50 then MAP as tolerated to avoid over-inflation. Wean power/amplitude to keep PaCO2 45-60 mmHg. Follow blood gases Q30-60 min after SRT until stable and wean appropriately to avoid hypocarbia.
Rescue Therapy For Premature Infant With RDS
To be used for premature neonates who can’t ventilate on either CMV or the Infant Star HFV or who require a MAP > 20 cm to achieve oxygenation while on the Infant Star. Use initial frequency of 15 Hz, Power of 3.0 - 4.0, MAP 2 cm above MAP on the Infant Star HFV, or MAP 4 cm above the MAP on CMV.
The goal is to minimize volutrauma, barotrauma, atelectatrauma, biotrauma and oxygen toxicity. Use minimum power/amplitude to keep PaCO2 adequate (e.g., 50-70 mmHg). Increase MAP as necessary to keep FiO2<0.50 if possible. Use I.T. of 33%. Use frequency of 10-15 Hz. Use lower frequencies (6-10 Hz) if having difficulty with oxygenation or use the higher frequencies if having problems with hypocarbia or PIE.
Other Potential Indications
CHF/Pulmonary Edema, Chest Physiotherapy, Hypoplastic Lungs and Post-op Heart Patients
Not Beneficial For Asthma
Increased risk of air trapping with reactive airway disease.
Once oxygenation is adequate and the patient is ready to be weaned follow these steps:
1) First only wean FiO2 until < 0.50-0.60 unless hyper-inflated.
2) Once FiO2 < 0.50-0.60 or hyper-inflated, decrease MAP by 1 cm Q4-8h; if OXYGENATION is lost during weaning then increase MAP by 3-4 cm to restore lung volumes and begin weaning again, but proceed more slowly with decreases in MAP.
3) Minimal MAP ≈ 8-16 cm with FiO2 < 0.40-0.50, at this point one can convert to CMV or remain on HFOV while the patient continues to heal and grow (e.g., 8-12 cm < 2.5 kg, 13-16 cm > 2.5 kg).
Reduce POWER by 0.2-0.3 units per change whenever PaCO2 decreases below threshold, until minimal POWER is reached (1.5-4.0) depending on the size of the patient. If frequency is below the standard frequency for the patient's weight, then first wean by increasing frequency back to baseline which also decreases the tidal volume, then decrease power as described.
1) Extubation – Most infants are ready to be extubated for a trial of NPCPAP when they meet the following criteria:
- MAP < 10 cm
- FiO2 < 0.40
- Power < .5 for term, < 1.5 for preterm
- Extubate to NPCPAP of 6-9 cm.
2) Conventional Ventilation – Most term neonates are ready for conversion to conventional mechanical ventilation (SIMV) when they meet the following criteria:
- MAP < 16-17 cm
- FiO2 < 0.40 - 0.45
- Power < 4.0
- To convert to conventional mechanical ventilation (CMV) use a MAP 3-4 cm less than the MAP on HFV [e.g., MAP = 16-17 on HFV, use a MAP of 12-13 on CMV (PIP = 26, PEEP = 8, Rate = 40, IT = 0.4)]
COMPLICATIONS ASSOCIATED WITH HFOV
Hyperinflation or Barotrauma
Increase frequency of suctioning
Decrease MAP, and rule out other causes (e.g., pneumothorax, sepsis, dehydration, etc.).
EFFECTS OF CHANGING FREQUENCY ON VENTILATION USING THE SENSORMEDICS HIGH FREQUENC OSCILLATORY VENTILATOR.