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1. HFOV (high frequency oscillatory ventilation) is indicated for
ventilatory support and treatment of respiratory failure and
barotrauma.
The use of HFOV in the adult patient is an object of some debate
and as a rule is discouraged. It is recognized however, that
situations may arise where, short of ECMO, it is the only
modality left available to the practitioner.
Generally, it is felt that HFOV should not be used in patients with
a body weight over 50 kilograms. Weights above this will
generally require an amplitude pressure higher than the 3100A's
maximum output and lead to possible overheating, off-center
positioning, and potential failure of the piston.
Strategies in the use of HFOV in the larger patient are similar to
that used in the neonatal/pediatric population and are aimed at
maximizing oxygenation and adequate elimination of carbon
dioxide with the primary aim of incorporating lung protective
strategy.

2. OXYGENATION
Oxygenation will depend on the use of two parameters -
the FiO2 and the mean airway pressure (MAP). Initial MAP
settings should be established at between 5-10 cmH20
more than the mean on conventional ventilation and further
adjusted according to the SPO2 and x-ray findings revealing
atelectasis or hyperinflation.
It is recommended that MAP not be weaned until the
FiO2 is less than 60%.
Occasionally, when the patient is on a high FiO2 (>70%) the
MAP may have to be decreased to avoid hyperinflation
and/or barotrauma and a relative degree of hypoxemia and
hypercapnia may have to be accepted.

3. VENTILATION
The primary control for ventilation is the delta P or
amplitude pressure control.
Increasing the amplitude should result in greater volumes
and a decrease in PCO2.
If this is unsuccessful, lowering the frequency, i.e.
Hz/respiratory rate, can help. Remember 1Hz=60 BPM. In
the adult, rates between 5-8 Hz are acceptable. The
minimum frequency provided by the 3100A is 3 Hz.
A third method would be to increase the I-time from the
standard 33% up to a maximum of 50%. Even though
allowing for less expiratory time, increasing the I-time will
allow for the generation of a greater tidal volume. This may
also, paradoxically, reduce PO2.
It should be remembered that decreasing the frequency
is not a method of weaning as this, in fact, increases
ventilation.

4. Though somewhat debatable, and not as problematic as in
jet ventilators, there may be some difficulties with
humidification, leading to inspissated secretions. A
concomitant goal of medical therapy should be adequate
peripheral hydration.
While there are no positive contraindications to its use, side
effects may include hyper/hypoventilation, IVH, BPD,
necrotizing tracheal bronchitis, atelectasis, hypotension,
pneumothorax, pneumopericardium, pneumomediastinum,
pneumoperitoneum and PIE.

5. It is recommended that patients undergoing this therapy be
monitored with transcutaneous PO2 and PCO2 monitoring
as well as venous and arterial blood gasses when
necessary. Mechanical ventilation will be implemented,
maintained and adjusted by a Respiratory
Therapist. Decisions regarding changes in ventilation
therapy are a collaborative effort by the Respiratory
Therapist, Physician and Registered Nurse.
Specifications
Bias flow 0 - 40 lpm
Mean airway pressure 3 - 45 cmH20
Frequency 3 - 15 hz
% inspiratory time 30 - 50%
Power / Delta P 0 - 100 oscillator driver power

6. CALIBRATING PATENT CIRCUIT
1. Turn on source gas and set Bias Flow to 20 1pm
2. Set Mean Pressure Adjust and Mean Pressure Limit to
maximum (fully clockwise)
3. Push in and hold RESET while observing Mean
Pressure digital readout
4. Adjust Patient Circuit Calibration screw on right side of
control module to achieve a mean pressure between 39
and 43 cmH20.
5. Release reset button

7. VENTILATOR PERFORMANCE CHECK
1. Set frequency to 10 and % I-time to 33.
2. Set Bias Flow to 20 lpm
3. Depress RESET button long enough to allow MAP to
increase above 6 cmH20
4. With Mean Pressure Adjust control establish a mean
pressure of between 19 and 21 cmH20
5. Depress START/STOP button to cause oscillator to run
6. Increase POWER control setting to 6.0 and center
piston with Piston Centering control
7. With piston centered and a stable Delta P reading verify
that Delta P is between 56 and 75 and that MAP is between
17 and 23.
8. Depress START/STOP button to stop oscillator.
9. The 3100A is now ready for patient use.

8. THERAPEUTIC STRATEGIES
Ventilation is largely governed by changes in Delta P.
Increasing Delta P increases ventilation and vice versa. If
maximum Delta P will not provide sufficient ventilation, a
secondary strategy is to decrease the frequency. This takes
advantage of the fact that less Delta P is attenuated by ET
diameter at lower frequencies. If PCO2 is still elevated, % I-
time may be increased up to 50%.
Oxygenation is largely a function of MAP. Typically we
begin at a MAP 10% higher than that used in conventional
ventilation. Attempt to wean FiO2 to less than 70% before
weaning MAP

9. Managing Large Patients (>35 kg) on the 3100A Oscillator
What is the FDA's limit on patient weight for use of the 3100A?
While the pediatric prospective randomized controlled trial (RCT) was
limited to 35 kg, the FDA's Review Panel recognized that the range of
ventilation with the 3100A was more limited by physiologic
considerations rather than by absolute patient weight. As the MDDI
Gray Sheet reported in January 1995, "SensorMedics high frequency
ventilator approval for pediatric use should not limit indications to
patients who weigh less than 35 kilograms, FDA's Anesthesiology and
Respiratory Therapy Device Panel agreed at a Jan 20 meeting."
During the panel hearing for pediatric approval they noted that it
requires approximately 2 ml/kg to ventilate a patient with HFOV. With a
6 mm endotracheal tube, at maximum power and at a frequency of 3
Hz, approximately 180 ml could be delivered by the 3100A to a test
system with a compliance of 20 ml/cmH2O. This equates to a
theoretical 90 kg patient weight limit. As can be seen in Figure 1, a
larger endotracheal tube (9 mm) will enable even larger volumes to be
delivered, raising the theoretical weight limit.

11. In summary, there is no upper weight limit for the 3100A.
No special forms, IRB approval or informed consent is
required for treating any child with an OI>13 with the
3100A.
What has been the largest patient managed with the
3100A?
While we are not aware of all large patients managed with
the 3100A, we do know of 2 patients weighing 110 and 113
kg (242 and 249 lb.) who were adequately ventilated with
the 3100A. We've started a database of large patients
(Table 1) and the mean weight of the survivors is 64.4 kg
(129 lb.)
Table 1. 3100A Large Patient Registry

12. When should I consider using the 3100A?
As with all candidates for the 3100A, the earlier, the better. When we went back
through the pediatric RCT data to answer this question, we found that waiting
more than 72 hours on CMV raised the odds ratio for chronic lung disease in
survivors to 25.2. In both the pediatric RCT and our adult 3100B pilot rescue
trial, waiting more than 10 days to initiate HFOV was statistically specific for
increased mortality.
The specific markers for use of the 3100A are:
Gross Air Leaks
ARDS or Intractable RSV Pneumonia
With increasing FIO2 requirements (>60%).
Use of PCIRV to recruit lung volume.
Use of paralysis for patient management.

13. Clinical experience in both pediatric and adult applications
has taught us that the ability of the 3100A to achieve
desired levels of PCO2 in larger patients is tied closely to
the prior amount of conventional ventilation. When larger
patients are selected early for this therapy, CO2 elimination
is more easily accomplished.
What are the recommended starting settings for use of
the 3100A in large patients?
FIO2 at 1.0
MAP starting 4-8 cmH2O above that on CMV.
Flowrate > 18 LPM, higher if required to meet MAP setting.
Frequency starting at 6 Hz.
Delta-P starting at a power setting of 4.0 and rapidly
increasing it to achieve adequate chest movement.
%I-Time set to 33%.

14. If CO2 retention persists at maximum settings, decreasing
the cuff pressure to allow gas to escape around the ET
tube will move the point of fresh gas supply from the wye
connector to the tip of the ET tube (Figure 2). This will
reduce the deadspace and lower PaCO2. Note: The bias
flow may have to be increased to compensate for the leak
and maintain MAP.

16. What are the markers that the patient is failing on the
3100A?
Failure to oxygenate is defined by the inability to decrease
FIO2 by 10% within 24 hours. An OI < 42 at 24 hours of
HFOV is a good indicator of a positive response. An OI >42
at 48 hours has been specific for oxygenation failure and
non-survival.
Failure to improve or maintain adequate ventilation is
defined as the inability to maintain PaCO2 < 100 torr with a
pH > 7.25. It is extremely important to monitor PaCO2 in
larger patients.
As reported in the large patient registry, most patients who
survived had a significant oxygenation (OI) response within
the first few hours of HFOV.

17. 3100A High Frequency Oscillatory Ventilation
Large Patient (>30 kg) Guideline Considerations and
Patient Management
Inclusion Criteria:
OI > 13 (OI = 100 x FiO2 x Paw / PaO2) in two
arterial blood gases within a six hour period.
Examples:
A patient with a PaO2 of 60 torr on an FIO2 of
>.60 and a mean airway pressure > 13 cmH2O
A patient with a PaO2 of 60 torr on an FIO2 of
>.40 and a mean airway pressure > 20 cmH2O *** If pH <
7.28 consider buffering the patient with THAM before
starting.
*** Assure adequate blood pressure
*** Special attention to ventilatory requirements and
PaCO2 should be emphasized in larger patients

18. Although patients with the following conditions have
been adequately managed with the 3100A,
consideration should be given to these factors prior to
institution of HFOV therapy:
Patient diagnosed with increased Airway
Resistance.
Elevated ICP
Weight > 70 Kg
Mean Arterial Pressure < 55 mm Hg
Passive pulmonary blood flow dependency with
normal compliance

19. Clinical Experience with the 3100A Suggests that:
1. There appears to be an inverse relationship
between prior days on CMV and ability to ventilate with the
3100A. As the limitation in size of patient is usually
constrained by ventilation requirements, the longer the time
on CMV prior to institution of HFOV, the smaller the patient
that may be able to be managed.
2. Patients managed for more than 72 hours on CMV
for ARDS prior to transfer to HFOV have a more than 25
fold odds increase for developing chronic lung disease.
3. Patients managed for more than 10 days on CMV
for ARDS prior to transfer to HFOV have a statistically
significant increased risk of mortality.
4. Patients with an oxygenation index (OI) greater
than 42 after 48 hours of HFOV have a significantly
increased risk for non-survival and alternative therapeutic
options should be considered.
_______________________________________________

20. Information to obtain and patient preparation before
placing the patient on HFOV
1. If patient has a PA catheter, measure and record
cardiac output, PCWP, SVO2
2. CVP line -- CVP should be at least 8 mm Hg
3. TcPCO2 monitor at 38-40 degrees C° to follow
trend information
4. Arterial line for MAP monitoring and ABG analysis
Initial Set-Up
1. Obtain HFOV Flowsheet
2. Fill in conventional ventilator setting, blood gases,
medications, hemodynamics
3. Just prior to instituting HFOV, suction patient well
and give one 10 second sustained recruitment inflation.
4. All patients may require neuromuscular blockade
and sedation for initiation of HFOV.

25. Editor:
Abdul fattah Abro
Neonatal intensive care unit staff
Nurse
Karachi sindh