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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

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Page 1: Hfov  presentation (abdul fattah)

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.

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OXYGENATIONOxygenation 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.

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VENTILATIONThe 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.

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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. 

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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 lpmMean airway pressure  3 - 45 cmH20Frequency  3 - 15 hz% inspiratory time  30 - 50%Power / Delta P 0 - 100 oscillator driver power  

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CALIBRATING PATENT CIRCUIT1.   Turn on source gas and set Bias Flow to 20 1pm2.    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

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VENTILATOR PERFORMANCE CHECK1.   Set frequency to 10 and % I-time to 33.2.   Set Bias Flow to 20 lpm3.   Depress RESET button long enough to allow MAP to increase above 6 cmH204.   With Mean Pressure Adjust control establish a mean pressure of between 19 and 21 cmH205.   Depress START/STOP button to cause oscillator to run6.   Increase POWER control setting to 6.0 and center piston with Piston Centering control7.   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.

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THERAPEUTIC STRATEGIESVentilation 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

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Managing Large Patients (>35 kg) on the 3100A OscillatorWhat 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.

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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

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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 LeaksARDS or Intractable RSV PneumoniaWith increasing FIO2 requirements (>60%).Use of PCIRV to recruit lung volume.Use of paralysis for patient management.

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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 1.0MAP 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%.

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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.

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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.

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3100A High Frequency Oscillatory VentilationLarge 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

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 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

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 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.______________________________________________________________________

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 Information to obtain and patient preparation before placing the patient on HFOV1.           If patient has a PA catheter, measure and record cardiac output, PCWP, SVO22.           CVP line -- CVP should be at least 8 mm Hg3.           TcPCO2  monitor at 38-40 degrees C° to follow trend information4.           Arterial line for MAP monitoring and ABG analysis Initial Set-Up1.           Obtain HFOV Flowsheet2.           Fill in conventional ventilator setting, blood gases, medications, hemodynamics3.           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.

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Editor: Abdul fattah Abro Neonatal intensive care unit staff NurseKarachi sindh