Jonathan M. Klein, MD
Peer Review Status: Internally Peer Reviewed

SensorMedics 3100A Oscillatory Ventilator

The SensorMedica 3100A is a true high frequency oscillator with a diaphragmatically-sealed piston driver.  It is theoretically capable of ventilating patients up to 35 kg.  Tidal volume (TV) typically delivered ≈ 1.5-3.0 cc/kg (TV<dead space).  It is an extremetly efficient ventilator secondary to an active expiratory phase, but it is not capable of delivering sigh breaths for alveolar recruitment.

Initial settings

Frequency

 Initial settings:

10 Hz (600 BPM) for term infants ( > 2.5 kg)

12 Hz (720 BPM) for premature infants (1.5 -  ≤ 2.5 kg)

14 Hz (840 BPM) for preterm infants ( 1.0 - < 1.5 kg)

15 Hz (900 BPM) for preterm infants < 1.0 kg

8 Hz (480 BPM) for children between 6-10 kg

6 Hz (360 BPM) for children > 10 kg (consider 4 or 5 Hz if not ventilating)

Lower frequencies will increase absolute IT and often will improve oxygenation via increased alveolar recruitment as well as significantly improve ventilation through increased tidal volume delivery.

If not ventilating at the initial starting frequency on a Power/Amplitude/Delta P that clearly results in good chest wall vibrations then decrease the frequency by 2 Hz, at a time, to significantly increase the delivered TV.  Remember during HFOV, alveolar ventilation (Ve) ≈ (TV)2F as compared to conventional ventilation where Ve ≈ TV(R).

Inspiratory time (I.T.)

Set initially at 33% 

Absolute I.T. =

  • 22 msec at 15 Hz
  • 33 msec at 10 Hz
  • 41 msec at 8 Hz
  • 55 msec at 6 Hz

1)  Warning - The percent of I.T. should never be increased beyond 33% because it can lead to air trapping and fulminant barotrauma from an inadequate time spent in exhalation.  Total absolute I.T. should only be increased by decreasing frequency, thus leaving the I:E ratio constant to avoid air trapping.

a) I.T. can be decreased to 30% to heal airleaks by lengthening the I:E ratio (30%:70%).

b) For premature infants < 1000 grams, set I.T. initially at 30% to minimize air trapping by also using a longer initial I:E ratio (30%:70% or 1:2.3).

2)  Standard I:E ratio: ≈ 1:2 (3-15 Hz) with a 33% I.T and 67% E.T.

Power/Amplitude/Delta P

A rough representation of the volume of gas generated by each high frequency wave.  Power range (1.0 - 10.0). Oscillatory Pressure/Delta P/Amplitude range (0-90 cm) H2O. Maximum true volume of gas generated by the piston is 365 cc.  Maximum amplitude (delta P/pressure wave) or tidal volume delivered is highly variable and is highly attenuated by the ETT and the tracheobronchial tree before reaching the alveolus. Thus the delivered TV depends on the following factors: circuit tubing (compliance, length and diameter), humidifier (resistance and compliance - water level), ET tube diameter and length (FLOW is directly proportional to r4/l, where r = radius of airway and l = length of airway), the patient's airways and compliance.

  1. Initial Setting for POWER/Amplitude:
  • 1.5 - 2.0 (delta P 15-20 cm) for wt  <2.0 kg
  • 2.0 - 2.5 (delta P 20-25 cm) for wt 2.0-2.5 kg
  • 2.5 - 3.5 (delta P 25-35 cm) for wt 2.5-3.5 kg
  • 3.5 - 5.0 (delta P 35-45 cm) for wt 3.5-5.0 kg
  • 6.0 (delta P 60 cm) for wt 5.0-7.5 kg, 7.0 (delta P 70 cm) if wt ≥  7.5 kg.

Chest wall needs to be vibrating.  If not vibrating, increase power.

* Check ABG's every 15-20 min until PaCO2 ≈ 40-60 or within target range, i.e., titrate Power/Amplitude setting based on PaCO2 desired.  Many HFOV centers have you order amplitude or delta P (∆P) to regulate ventilation instead of power.  Since amplitude or delta P is a measured value, we have decided that the Power setting is a more reliable and consistent way of adjusting this ventilator and thus we order changes in power in order to regulate ventilation by changing the distance the piston travels but either approach is completely valid.

2) Alveolar ventilation is directly proportional to POWER (Ampltiude or delta P), therefore the level of PaCO2 is inversely proportional to the power/amplitude/delta P.

3) During HFOV, alveolar ventilation (Ve) ≈ (TV)2f as compared to conventional ventilation where Ve ≈ TV(R).  Thus we primarily adjust the power (amplitude/delta P) to change the delivered tidal volume in order to manipulate ventilation.

4)  Management of ABG's (Ventilation - Ve) Guidelines:

a)  Change POWER by 0.2-0.3 to change CO2 ± 2-4 mm Hg or amplitude/delta P by 2-3 cm H2O

b)  Change POWER by 0.4-0.7 to change CO2 ± 5-9 mm Hg or amplitude/delta P by 4-7 cm H2O

c)  Change POWER by 0.8-1.0 to change CO2 ± 10-15 mm Hg or amplitude/delta P by 8-10 cm H2O

d) Warning - It is extremely important to normalize PaCO2 rapidly by weaning Power/amplitude/delta P in order to avoid volutrauma from excessive tidal volumes.  Thus check ABG's frequently (Q15-20 min) and decrease POWER/amplitude/delta P accordingly until PaCO2 ≥ 35.  PaCO2 < 35 mm Hg correlates with an increased risk of pneumothorax.  Thus to minimize the risk of volutrauma, it is important to minimize the amount of delivered TV by regulating the POWER/Amplitude/Delta P needed in conjunction with the optimal frequency based both on patient size and the pathophysiology of the lung disease being treated to maintain balance between shear force and effective ventilation.

e)  If PaCO2 still remains elevated at high POWER setting (>7.0), decrease FREQUENCY by 2 Hz every 15-20 min until maximum tidal volume is reached (4 Hz at a POWER of 10.0).  The lower frequency leads to a longer absolute I.T. which results in a larger tidal volume of gas displaced towards the infant.  This increased TV leads to increased alveolar ventilation (on HFOV, Ve ≈ (TV)2f).

5)  Manual Ventilation:  Hand bagging while on the SensorMedics Ventilator should be minimized secondary to the risk of barotrauma due to shear force injury from higher TV and possible hyperinflation. Oxygen desaturation can also occur from loss of MAP leading to alveolar derecruitement.  Suctioning should be performed using just the ventilator breaths alone (an inline suctioning adapter is optimal).  If bagging has to be done, the PIP while bagging if possible should be 8-10 cm above the MAP and a PEEP of 6-8 cm should be maintained as tolerated.

MAP

Oxygenation on HFOV is directly proportional to MAP which is similar to conventional ventilation, however with the SensorMedics HFOV the MAP is directly ordered and generated.  Thus during HFOV:MAP ordered = MAP delivered.

1.  Initial Settings:

a)  Neonates - Initial MAP should be 2-4 cm above the MAP on CMV.

b)  Infants/Children - Initial MAP should be 4-6 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 a MAP):

a)  If not oxygenating adequately at initial MAP (10-18 cm) obtain CXR to assess lung volume.  If lung is not hyperinflated (flattened diaphragm) or is below optimal lung volume ≈ 9 ribs then increase MAP by 1-2 cm every 20-30 min until adequate oxygenation is achieved or lung starts to become overinflated (e.g. FiO2 0.6-0.7 increase by 1-2 cm, FiO2 1.0 increase by 2-4 cm per change).

b)  Maximum potential MAP = 38-43 cm

c) Warning - If oxygenating adequately, but the lung is hyperinflated immediately decrease MAP by 1-2 cm every 1-2 h until lung volumes return to normal. If the lung is allowed to remain hyperinflated for prolonged periods of time the risk of barotrauma increases.

d) If not oxygenating with lung becoming hyperinflated, you can decrease frequency as a way to increase I.T. to improve alveolar recruitment while keeping I:E ratio constant.

Management strategies

The SensorMedics HFOV is used for premature infants, term infants or young children with respiratory failure not responsive to conventional ventilation or first intention therapy for premature infants with RDS. 

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 (amplitude/delta P 35-45 cm).  Initial MAP 4 cm above MAP while on CMV.  Check CXR 1-2 hrs after converting to HFOV, then adjust MAP to achieve optimal lung volume (9 ribs expanded with improved aeration).  If not oxygenating, increase MAP by 1-2 cm every hour until oxygenation improves.  Adjust Power/Amplitude/delta P to keep PaCO2 45-55. Consider decreasing frequency to 8 Hz and then to 6 Hz if ventilation and oxygenation remain problematic. This will increase TV to improve ventilation and absolute IT to help to improve oxygenation via alveolar recruitment.

Airleaks

Pneumothorax or PIE - The goal is to minimize both tidal volume and shear force/peak pressure generated by a given TV at a set MAP.  Transiently tolerate increased FiO2 requirements (0.6 - 1.0) by reducing MAP as tolerated in order to minimize overdistention from excessive MAP.  Practice permissive hypercarbia and accept higher PaCO2's to minimize the delivered TV.  Increase  FREQUENCY up to 12, 14 or 15 Hz in order to minimize both absolure I.T. and delivered TV in order to heal the airleak. Decrease I.T. to 30%. It is better to be on a higher frequency with a concurrent higher level of amplitude to maintain the same level of PaCO2 then a lower frequency with lower amplitude.  Since the actual delivered TV to the lung will be less and the leak will heal more rapidly with the higher rather than lower frequency.

Reference: Ellsbury DL, Klein JM and JL Segar, Optimization of high-frequency oscillatory ventilation for the treatment of experimental pneumothorax. Crit Care Med 2002; 30:1131-1135.

ARDS

C.   Goal is to minimize volutrauma, shear force and oxygen toxicity.  Use the minimum POWER possible at the appropriate FREQUENCY in order to keep PaCO2 adequate (e.g. 55-70 mm Hg).  Increase MAP as high as necessary to keep FiO2≤1.0.  Also decrease frequency to increase absolute I.T. to improve oxygenation.

RDS

C.   Give surfactant replacement therapy using manual bagging.  Start with frequency of 12-15 Hz depending on EGA/birth weight and I.T. of 33%.  Use inital MAP of 8-10 cm or 2 cm above MAP on conventional ventilation. Obtain chest radiograph and adjust MAP to obtain 9 rib expansion with improving FiO2. Wean FiO2 until <0.40 then MAP as tolerated to avoid overinflation. Wean power/amplitude/delta P to keep PaCO2 45-60 mmHg.  Follow blood gases q30-60 min after SRT until stable and wean power/amplitude/delta P frequently to avoid hypocarbia (PaCO2< 40 mm Hg).

Rescue therapy for premature infant with RDS

To be used for premature neonates who can’t ventilate on high conventional or on excessively high HFJV settings or who require a MAP ≥ 20 cm to achieve oxygenation while on HFJV.  Use initial frequency of 10-12 Hz, Power of 3.0 - 4.0 (delta P 30-40 cm H2O), MAP 2-4 cm above MAP on HFJV or 4 cm above the MAP on conventional ventilation.

BPD (evolving):

Goal is to minimize volutrauma, barotrauma (shear force), atelectatrauma, biotrauma and oxygen toxicity.  Minimize the power/amplitude/delta P to keep PaCO2 adequate (e.g., 50-70 mmHg).  Increase MAP as necessary to keep FiO2 <0.50-0.60 if possible avoiding hyperinflation leading to increased PVR.  Use I.T. of 33%.  Use frequency range of 10-15 Hz: use lower frequencies if having difficulty with ventilation and/or oxygenation, use higher frequencies with I.T. of 30% if having problems with PIE.

Other potential indications

CHF/Pulmonary Edema, Hypoplastic Lungs, anascara, hydrops fetalis and so forth …

Not beneficial for asthma

Increased risk of air trapping with severe reactive airway disease.

Weaning

Oxygenation

Once oxygenation is adequate and the patient is ready to be weaned follow these steps:

1) First wean FiO2 until ≤ 0.60 unless hyperinflated. During active changes in compliance (e.g., surfactant replacement, aggressive diuresis, …) may need to follow chest radiographs as frequently as every 8-12 hours to evaluate lung expansion to avoid hyperinflation leading to decreased cardiac output from impaired venous return with loss of preload or development of pneumothorax. Always wean MAP if hyperinflation is developing. Aim for 9 rib expansion.

2) Once FiO2 ≤ 0.60 or hyperinflated, decrease MAP by 1 cm Q4-8h; if OXYGENATION is lost during weaning then increase MAP by 2-4 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 conventional ventilation or remain on HFOV while the patient continues to heal (e.g., MAP of 8-12 cm ≤ 5 kg).

Ventilation

Reduce POWER by 0.2-0.3 units per change (amplitude/delta P 2-3 cm H2O) whenever PaCO2 decreases below threshold (e.g., < 45 mm Hg) until minimal POWER/amplitude/delta P is reached (power <1.5-2.0, delta P < 15-20 cm H2O) depending on the size of the patient.  If frequency is below the standard frequency for the patient's weight, then considering weaning by increasing frequency back to baseline which will also decrease the tidal volume, then decrease power/amplitude/delta P as described above.

1) Extubation –Neonates are ready to be directly extubated for a trial of Nasal CPAP or Noninvasive Ventilation (NIV) when they usually meet the following criteria:

a)  MAP ≤ 10 cm, FiO2 ≤ 0.40 and power ≤ 2.0 (delta P ≤ 20 cm H2O to a Nasal CPAP of 7-9 cm H2O or appropriate NIV settings.

2) Conventional ventilation – Importantly neonates are ready for conversion to conventional mechanical ventilation when they meet the following criteria:

a) MAP ≤ 16-17 cm, FiO2 ≤ 0.40 - 0.50 and power ≤ 4.0 (delta P < 40 cm H2O. Conversion often will not succeed if MAP is still > 18 cm while on HFOV.

b) To convert to conventional mechanical ventilation aim for 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 (e.g., PIP = 26, PEEP = 8, Rate = 40, IT = 0.4), PS 12]

Potential complications associated with HFOV

Hyperinflation

Can lead to increased pulmonary vascular resistance and air leaks, decrease MAP

Secretions

Increase suctioning (inline suctioning is optimal to minimize loss of lung recruitment

Hypotension

Quickly lower MAP, and rule out other causes [e.g., pneumothorax, sepsis, dehydration, cardiac dysfunction (LV or RV) etc …]

Air leaks

Decrease MAP to minimize over distention and increase frequency to decrease delivered tidal volume

Hypocarbia

Wean ventilation and follow pCO2 closely until level is appropriate

EFFECTS OF CHANGING FREQUENCY ON VENTILATION USING THE SENSORMEDICS HIGH FREQUENC OSCILLATORY VENTILATOR.

EFFECTS OF CHANGING FREQUENCY ON VENTILATION USING THE SENSORMEDICS HIGH FREQUENC OSCILLATORY VENTILATOR.