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Revision History Date

Revision

Changes

February 1991

A

Initial Release

May 1991

B

Corrected page numbers in TOC. Corrected figure references. Patient Circuit Assy. modified. Warning added. Instructions for changing the patient circuit added. Intervention chart added.

June 1991

C

Changed filter replacement interval to every 500 hours. Changed part number of filter element.

July 1991

D

Updated labeling for disposable components. Update picture for new filters. Change support arm to cradle rod. Update picture to show cradle rod. Add cradle rod to installation. Corrected missing filter, changed warning. Repaginated. Correct adjustments for new patient circuit. Added new patient circuit to performance checks. Added P/N for Humidifier tubing.

August 1991

E

Corrected patient circuit setup limits. Update label for new setup limits. Changed power requirements to reflect circuit breaker change.

November 1991

F

Removed IEC 601-1 and BSI approval. Changed 50 to 56 in step h. Corrected description of filter elements to pack of 10.

May 1995

H

Added pediatric Indications for Use. Updated RI warning. Corrected ET tube size references. Pediatric graph added. Corrected humidifier reference. Corrected gas flow reference. Added color coding. Corrected pre-use cleaning instructions. Added pediatric clinical guidelines. Reformatted Warnings & Precautions.

September 1996

J

Removed City of LA label. Added new power supply. Updated control package DC Tech Support. Power supply procedure. Updated step 7-g of start-up procedure.

March 2002

K

Reformatted to conform with Critical Care Division Operator Manual format. Re-Ordered Chapters. Revised page numbering. Added Checklist Label and 6000 hour Driver Replacement label. Added air cooling inlet flow for 3ohm driver. Added pneumatic block diagram with PR7. Updated pneumatic diagram with PR1 to current revision. Added reference to 6000 and 12000 hour scheduled maintenance. Added P/N s for flexible patient circuit. In-line suction systems addressed. Changed all references to BIAS PRESSURE to read MEAN AIRWAY PRESSURE. Changed usage of “neonate” to read “patient” where appropriate. Added front matter to conform with Critical Care standards. Modified suctioning guidelines.

April 2006

L

Revised for ECR 61201. Added scheduled maintenance for Power Module Assy.

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Contents Revision History... iii Warranty... vii Notices ... viii Safety Information... x Chapter 1 Introduction, Systems & Safety Features ... 1 System Diagrams ... 1 Introduction to the 3100A System ... 3 Safety Features... 10

Chapter 2 Assembly and Installation ... 13 Unpacking... 13 Assembly ... 13 Pre-Use Cleaning... 17

Chapter 3 Controls, Indicators and Connections ... 19 Front and Side Panel – Control Package... 19 Rear Panel – Control Package... 25 System Column and Patient Circuit... 27

Chapter 4 Operational Verification and Start-up... 31 Start-up Procedures... 31 Performance Verification... 36

Chapter 5 Clinical Guidelines ... 37 Treatment Strategies... 37 Disease-Specific Variations to General Clinical Strategies ... 43 Adverse Effects ... 43 Recommended Monitoring Frequency ... 44 Suctioning Guidelines ... 44

Chapter 6 Maintenance & Troubleshooting... 47 Exterior Cleaning... 47 Operator Maintenance Procedures... 47 Patient Circuit Calibration ... 50 767124-101

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Other Scheduled Periodic Calibration ...50 Scheduled Periodic Maintenance...55 Troubleshooting ...57

Appendix A Contact and Ordering Information...63 Technical Support ...63 Ordering Parts and Supplies ...63

Appendix B Specifications ...65 Controls...65 Indicators...67 Pressure Measurement ...69 Alarms...69 Electrical Specifications...71 Physical Specifications...73

Index ...81

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Warranty 3100A ventilation systems (the equipment) are warranted to be free from defects in material and workmanship and to meet the published specifications for one (1) year from the date of delivery of the equipment to the original purchaser. Exclusions: VIASYS Healthcare, Critical Care Division (the company) shall not be responsible for any damage or failure caused indirectly or directly by operation of the equipment outside of the allowable electrical, temperature and other environmental limits specified by the company, or by deficiencies in customersupplied services or supplies. The equipment is supplied with some components and accessories, which by their nature are not intended to, and will not, function for one year. If any such component or accessory manufactured by the company and supplied with the equipment fails to give reasonable service for a reasonable period of time, the company will, at its discretion, replace or repair such component or accessory. What constitutes reasonable service and a reasonable period of time shall be determined by the company after the company is in possession of all the facts concerning said component or accessory, and after said component or accessory has been returned to the company with transportation charges prepaid. The company makes no warranty concerning components or accessories not manufactured by or for the company. The company shall be released from all obligations under this warranty in the event that repairs or modifications to the equipment are made by persons other than personnel trained and/or authorized by the company. Any authorization by the company for repair or alteration by the Buyer must be in writing to prevent voiding of the warranty. In no event shall the company be liable to the Buyer for loss of profits, loss of use, consequential damage or damages of any kind based upon a claim for breach of warranty, other than the purchase price of any defective product covered hereunder. Exclusive Remedy: The liability of VIASYS Healthcare, Critical Care Division (the company) under this warranty is limited to replacing, repairing or issuing credit, at the discretion of the company, for parts that become defective or fail to meet published specifications during the warranty period. The company will not be liable under this warranty unless (A) the company is promptly notified in writing by Buyer upon discovery of defects or failure to meet published specifications; (B) the defective unit or part is returned to the company, transportation charges prepaid by Buyer; (C) the defective unit or part is received by the company for adjustment no later than four weeks following the last day of the warranty period; and (D) the company’s examination of such unit or part shall disclose, to its satisfaction, that such defects or failures have not been caused by misuse, neglect, improper installation, unauthorized repair, alteration or accident. Disclaimers VIASYS Healthcare warranties as herein and above set forth shall not be enlarged, diminished or affected by, and no obligation or liability shall arise or grow out of the rendering of technical advice or service by VIASYS Healthcare or its agents in connection with the Buyer's order of the products furnished hereunder. The foregoing is in lieu of any warranty, expressed or implied, including, without limitation, any warranty of merchantability, except as to title, and can be amended only in writing by a duly authorized representative of VIASYS Healthcare, Critical Care Division.

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Notices Copyright Notice Copyright © 2005 VIASYS Respiratory Care Inc. This work is protected under Title 17 of the U.S. Code. No part of this document may be copied or otherwise reproduced, or stored in any electronic information retrieval system, except as specifically permitted under U.S. Copyright law, without the prior written consent of VIASYS Healthcare. For more information, contact VIASYS Respiratory Care Inc.

Company Addresses U.S. Office VIASYS Respiratory Care Inc. 22745 Savi Ranch Parkway Yorba Linda, California 92887 Telephone: (800) 520-4368 (714) 283-1830 FAX: (714) 283 8493

European Office VIASYS Healthcare GmbH Leibnizstr. 7 D- 97204 Hoechberg, Germany +49 (0) 931 4972 - 0 Fax +49 (0) 931 4972 - 423

Manufacturer: Bird Products Corporation A Subsidiary of VIASYS Healthcare 1100 Bird Center Drive Palm Springs, California 92262-8099 Telephone: (800) 520-4368 (714) 283-1830 FAX: (714) 283 8493 www.viasyshealthcare.com

Trademark Notices 3100A® is a registered trademark of SensorMedics Corporation, in the United States and some other countries. SensorMedics Corporation is a subsidiary of VIASYS Healthcare. All other brand names and product names mentioned in this manual are trademarks, registered trademarks, or trade names of their respective holders.

EMC Notice This equipment generates, uses, and can radiate radio frequency energy. If not installed and used in accordance with the instructions in this manual, electromagnetic interference may result. The equipment has been tested and found to comply with the limits set forth in EN60601-1-2 for Medical Products. These limits provide reasonable protection against electromagnetic interference when operated in the intended use environments described in this manual.

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MRI Notice This equipment contains electromagnetic components whose operation can be affected by intense electromagnetic fields. Do not operate the ventilator in an MRI environment or in the vicinity of high-frequency surgical diathermy equipment, defibrillators, or shortwave therapy equipment. Electromagnetic interference could disrupt the operation of the ventilator.

Intended Use Notice The SensorMedics 3100A High Frequency Oscillatory Ventilator (HFOV) is indicated for ventilatory support and treatment of respiratory failure and barotrauma in neonates. The specific patient conditions, which the HFOV is intended to treat, are respiratory distress syndrome (RDS) or respiratory failure caused by pulmonary interstitial emphysema (PIE) or air leak (AL). The SensorMedics 3100/3100A is also indicated for use in the ventilatory support and treatment of selected pediatric patients who, in the opinion of their physician, are failing on conventional ventilation. Patient size and other factors are important in the selection of patients to be treated using this ventilator. The SensorMedics 3100A Oscillatory Ventilator has no specific contraindications.

Restrictions Federal law restricts the sale of this device except by or on order of a physician.

Declaration of Conformity Notice This medical equipment complies with the Medical Device Directive, 93/42/EEC, and the following Technical Standards, to which Conformity is declared: EN60601-1 EN60601-1-2 The Manufacturer’s Quality System is certified to: ISO 9001 EN 46001 EU Notified Body: National Standards Institute of Ireland (NSAI) Type of Equipment:

Medical Equipment, Lung Ventilator

Trade names:

3100 and 3100A

If you have a question regarding the Declaration of Conformity for this product, please contact SensorMedics Corporation or VIASYS Healthcare, Critical Care Division.

IEC Classification

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The 3100A HFOV ventilator is suitable for use in institutional environments.

•

Ordinary equipment, not protected against the ingress of liquids.

•

Not protected/not suitable for use in the presence of flammable anesthetic gases.

•

Class 1, Type B Equipment.

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Safety Information Please review the following safety information prior to operating the ventilator. It lists information pertinent to the safe operation of the ventilator. Attempting to operate the ventilator without fully understanding its features and functions may result in unsafe operating conditions. If you have a question regarding the installation, set up, operation, or maintenance of the ventilator, contact Technical Support as shown in Appendix A Contact & Ordering Information.

Adverse Effects In the pediatric randomized trial, adverse effects identified were lung overdistention, air leak, and hypotension. There were no statistical differences in any of the adverse effects as compared to those reported in the conventionally treated patients with the exception of hypotension. The HFOV treated group had a few (but statistically significant) more frequent incidences of hypotension, however without evidence of serious compromise of cardiovascular status. In the neonatal randomized trial, adverse effects identified were lung overdistention, air leak, intraventricular hemorrhage (IVH), bradycardia, mucus plugging of the endotracheal tube, and hypotension. There were no statistical differences in any of the adverse effects as compared to those reported in the conventionally treated patients. High frequency ventilation, as with conventional positive pressure ventilation, has inherent risks in this patient population. These possible adverse effects include: under/over ventilation, under/over humidification, intra-ventricular hemorrhage (IVH) in the neonate, bronchopulmonary dysplasia (BPD), necrotizing tracheal bronchitis (NTB), atelectasis, hypotension, pneumothorax, pneumopericardium, pneumomediastinum, pneumoperitoneum, and pulmonary interstitial emphysema (PIE). The reported frequency of these occurrences are similar to conventional ventilation.

Terms WARNINGS

identify conditions or practices that could result in serious adverse reactions or potential safety hazards.

CAUTIONS

identify conditions or practices that could result in damage to the ventilator or other equipment.

NOTES

identify supplemental information to help you better understand how the ventilator works.

Warnings The following warnings must be read and understood before an attempt is made to operate the Model 3100A HFOV: •

Servicing of this instrument is restricted to factory-trained personnel only.

•

Sudden unexplained bradycardic events associated with no other clinical changes are possible in neonates who are being weaned or close to being weaned from HFOV therapy. These events may signal possible rapid improvements in patient lung compliance with overdistention during HFOV therapy and may require rapid weaning of Paw or switching to conventional ventilation.

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•

Do not attempt to defeat the proper connection of the ground wire as it may cause damage to the device or interconnected equipment and could be injurious to the patient or to those associated with the device use. This device is factory equipped with a hospitalgrade AC power plug. Grounding reliability can only be assured when connected to a tested receptacle labeled “Hospital Grade.”

•

Do not operate radio transmitters within 20 feet of this instrument. This may result in erroneous pressure readings leading to false alarms and automatic shutdown.

•

Do not shorten the 30” bias flow tube provided with the patient circuit as this may reduce the maximum ΔP by allowing the oscillatory pressures to be attenuated by closer proximity to the volume of the humidifier canister.

•

Do not attempt to substitute another circuit configuration as this could result in injury to the patient and/or the operator or equipment damage. The Patient Circuit described in this manual is specifically designed for patient use with the Model 3100A HFOV.

•

The operational verification and startup procedure must be followed before beginning ventilation of a patient. If at any time during the operational verification and startup procedure any abnormal function of the Model 3100A HFOV is noted, do not proceed with patient ventilation as this could cause patient injury or death. Contact SensorMedics Technical Support before proceeding any further.

•

An audible alarm indicates the existence of a condition which could be harmful to the patient and should never go unattended. Failure to respond to alarms could result in injury (including death) to the patient and/or damage to the ventilator.

•

Due to the possibility of explosion, the ventilator should not be used in the presence of flammable anesthetics.

•

Under no circumstances should the proximal airway gas temperature exceed 41°C. This could result in injury to the patient's upper airway membranes.

•

Failure to comply with the recommended maintenance procedures described in this manual could result in injury to the patient or operator, or damage to the equipment.

Cautions The following Cautions must be read and understood before an attempt is made to operate the Model 3100A HFOV:

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Follow closely the recommendations contained in Chapter 5, Clinical Guidelines, regarding the use of chest radiographs and cerebral ultrasound to monitor patient condition. During HFOV, as with all ventilators, the relationship between improvement in lung compliance, inadvertent increases in lung volume, increased pleural pressure, and decreased venous return is a matter of concern, since it may result in decreased cardiac output and a possible increase in the risk of IVH.

•

Patient weight is an important guideline as to lung volume and anatomical dead space, as well as the metabolic demand placed on ventilation. While the maximum displacement volume of the 3100/3100A is approximately 365 ml, the actual volume delivered to the patient is dependent on the power setting, frequency, endotracheal tube size, and patient respiratory system compliance. Therefore, you should pay special attention to ventilatory requirements and PaCO2 in larger children. Please review Chapter 5 of this manual, “Clinical Guidelines.”

•

The patient's tcPCO2 and tcPO2 or SpO2 must be monitored continuously to insure that blood gases are at the proper level. It is important that an unrestricted and unobstructed

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patient airway be maintained during HFOV. To ensure a clear patent airway, always maintain proper suctioning procedures as described in the Suctioning Guidelines section of Chapter 5, Clinical Guidelines. Since only proximal airway pressure is measured, no alarm will occur in the event of an obstruction or restriction. •

Ensure that the water-trap stopcock is closed prior to performing a Patient Circuit Calibration. If the stopcock is left open, Patient Circuit Calibration (39-43 cmH2O) may not be achievable, and the deliverable Paw will be reduced.

•

Deviation from the assembly methods described in this manual, could damage the Model 3100A, render it mechanically unstable, or cause it to malfunction. If any questions arise regarding assembly, please contact SensorMedics Technical Support before proceeding.

•

Care should be taken not to crimp or perforate any of the control or sensing lines (running to or from the Patient Circuit) during the assembly, operating or cleaning of the ventilator as this will cause malfunction of the Safety Alarms, Warning Alarms, Caution Alarms, and/or Pressure Limit Controls.

•

When connecting the Patient Circuit, make certain that it is properly supported and oriented by the support arm. Failure to do so could result in inadvertent Patient Circuit disconnection due to oscillatory forces or could result in collection of humidifier condensate in the patient airway.

•

If the temperature probe is wiped with alcohol, allow the alcohol to evaporate completely before inserting it into the circuit. Residual alcohol can weaken the acrylic adapter and cause fracturing.

•

Proper operation of the ventilator must be verified prior to each use. Refer to Chapter 4, Operational Verification and Startup Procedures. The alarm functions tested in this procedure verify the capability of the device to detect and indicate conditions which could have a harmful effect on the patient.

•

Touch the outer metal cabinet of the instrument before touching any other component to avoid possible instrument component damage from Electrostatic Discharge.

•

When the ventilator is connected to a patient, someone must be in attendance at all times to react to alarms or other indications of a problem.

•

The Inlet Filter Cartridges for the blended gas and the air inputs to the ventilator must be changed at least every 500 hours of operation as described in Chapter 6, Maintenance and Troubleshooting. Failure to replace a Filter Cartridge or substitution of an incorrect cartridge could result in injury to the patient and/or damage to the equipment. Use only SensorMedics Inlet Filter Cartridges.

•

The filter cartridge body must be screwed back on securely. Cross-threaded or loose installation will result in leaks and possible dislodging of the cartridge body. The ventilator WILL NOT FUNCTION if the cartridge body is dislodged.

•

The cover enclosing the control package, column, or any other portion of the ventilator must not be removed by the user. To avoid electrical shock hazard, please refer all service requiring cover removal to a factory trained, biomedical equipment service technician.

•

Recheck and readjust limit level after any ΔP change has been made. If the oscillatory amplitude (ΔP) is changed after the limit level has been set, the actual limit level will change slightly, in the same direction as the ΔP was changed.

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•

Troubleshooting the 3100A should be done “OFF PATIENT” to avoid any potentially dangerous situations such as abrupt changes in the Paw .

•

Do not use extraneous ventilator circuit attachments (such as a suction port) without a secondary external alarm capable of detecting ventilator disconnection. Due to their inline pressure characteristics, such attachments could possibly keep the Paw alarm from detecting an accidental ventilator circuit disconnection.

•

Fractional concentration of inspired oxygen should be verified with an oxygen monitor. Administration of excessive oxygen to a patient may be harmful. It is imperative that the prescribed gas mixture is delivered by the blending system.

•

The Water Trap must be drained at intervals as described in Chapter 6, Maintenance and Troubleshooting. If the ventilator is operating, leave a small amount of water at the bottom of the Water Trap container to act as a flow and pressure seal between the ventilator and the output of the drain.

•

To help prevent patient injury due to humidifier malfunction, use of a humidifier with the following characteristics is strongly recommended: (a) Thermally protected heater. (b) Alarms on overfilled water reservoir. (c) Alarms on under-filled water reservoir. (d) Alarms when electrically open or shorted temperature probe detected. (e) Alarms at probe temperatures > 41°C. (f) Alarms when dislodged temperature probe detected.

•

Do not place fluid-containing accessories, accessories that weigh more than ten pounds, or accessories that extend more than six inches above the ventilator electronics package or beyond its sides, on the Control Package of the ventilator. Doing this could cause damage to the ventilator, or could cause the ventilator to tip over, resulting in patient or user injuries and/or damage to the equipment.

•

Do not over turn or force the Patient Circuit Calibration adjustment screw as this may cause damage to the device. When it is nearing its adjustment limit, it will reach a mechanical stop.

•

Do not allow liquids to penetrate the casing of the ventilator as this may result in machine failure or malfunction.

•

Do not use a liquid sterilization agent on the outside of the ventilator as this may cause damage.

CAUTION: Federal law restricts this device to sale by, or on the order of a physician. CAUTION: Not suitable for use in the presence of flammable anesthetics. Service of this instrumentation is restricted to Factory Trained Personnel only.

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Symbols Symbol

Compliance

Meaning

Symbol #03-02 IEC 60878

Indicates ATTENTION, consult ACCOMPANYING DOCUMENTS

Symbol #5016 IEC 60417

This symbol indicates a FUSE.

Symbol #5019 IEC 60417 Symbol #01-20 IEC 60878

Symbol # 5333 IEC 60417 Symbol #02-03 IEC 60878

Symbol #5032 IEC 60417 Symbol #01-14 IEC 30878

This symbol indicates protective EARTH (ground). This symbol indicates TYPE B equipment, which indicates equipment that provides a particular degree of protection against electric shock, particularly with regards to allowable leakage current and reliability of the protective earth connection. This symbol indicates the equipment is suitable for alternating current.

Symbol #5007 IEC 60417 Symbol #01-01 IEC 60878

Indicates ON (Power)

Symbol #5008 IEC 60417 Symbol #01-02 IEC 60878

Indicates OFF (Power)

SensorMedics Symbol

Position Lock. Clockwise rotation locks instrument top. Counterclockwise rotation unlocks instrument top, allowing it to be swiveled for best view of front controls and displays.

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Chapter 1 Introduction, Systems & Safety Features System Diagrams

Figure 1.1. Pneumatic System Block Diagram for Part Number 770860.

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Figure 1.2 Pneumatic System Block Diagram for Part Number 766526

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3

Introduction to the 3100A System The 3100A HFOV system consists of eight linked subsystems. Six of these are included as part of the Model 3100A delivered to the customer, but two of them must be provided by the user. The two subsystems to be provided by the user are: •

An External Air/O2 Blender

•

An External Humidifier

The subsystems included with the ventilator are: •

The pneumatic logic and control system.

•

The patient circuit.

•

The oscillator subsystem.

•

The airway pressure monitoring system.

•

Electronic controls and alarms.

•

Electrical power supply.

External Air/Oxygen Blender Both oxygen and air sources are required for the 3100A. These sources feed a user-provided Air/Oxygen Blender. The air source also provides cooling to the Oscillator by means of a special pneumatic control system. The flow requirements for both the blender and for the air cooling of the Oscillator are described in Appendix B Specifications.

CAUTION Fractional concentration of inspired oxygen should be verified with an oxygen monitor. Administration of excessive oxygen to a patient may be harmful. It is imperative that the prescribed gas mixture is delivered by the blending system.

External Humidifier Although it functions with the patient circuit, the external humidifier is treated as a separate subsystem because it is provided by the user. The humidifier that is used must be a heated humidifier specifically manufactured for neonatal/pediatric use. It must be capable of a flow range up to 40 LPM. The temperature control can be either closed or open loop; however, proximal airway gas temperature must be monitored. Two ports for the temperature probe are provided on the Patient Circuit. These will be discussed later.

WARNING Under no circumstances should a proximal airway gas temperature of 41°C be exceeded. This could result in injury to the patient's upper airway membranes.

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CAUTION To help prevent patient injury due to humidifier malfunction, we strongly recommend using a humidifier with the following characteristics: a. Thermally protected heater. b. Alarms on overfilled water reservoir. c. Alarms on under filled water reservoir. d. Alarms when open or shorted temperature probe is detected. e. Alarms at probe temperatures > 41°C. f. Alarms when dislodged temperature probe is detected. Connecting the humidifier is described in more detail in Chapter 2, Assembly and Installation. Two standard adapters are provided for connecting the 3/8" I.D. tubing to and from the humidifier.

The Pneumatic Logic and Control System The Blender feeds pressurized blended gas to the Model 3100A Pneumatic Logic and Control Subsystem through an oxygen DISS fitting. Four pneumatic controls are part of this subsystem: •

Bias Flow Control

•

Mean Pressure Adjustment

•

Mean Pressure Limit Control

•

Patient Circuit Calibration Adjustment

Bias Flow Control This control sets the flow of the blended gas that continuously moves past the patient airway.

Mean Pressure Adjustment This control adjusts the mean airway pressure level on which the oscillatory waveform is superimposed. This mean airway pressure setting along with the oscillatory waveform characteristics determines the resultant Paw . This control determines the level of Patient Circuit expiratory limb Control Valve restriction in the manner described in the Patient Circuit section below.

Mean Pressure Limit This control determines the limiting proximal Paw within the Patient Circuit Subsystem. This control communicates with the Pressure Limit Valve of the Patient Circuit through a pneumatic control line in the manner described in the Patient Circuit section below.

Patient Circuit Calibration Adjustment This control is a screwdriver adjustment used to set the maximum mean pressure that can be attained with a particular Patient Circuit under specified conditions (see Chapter 6, Maintenance and Troubleshooting.) This control is used only when the Patient Circuit is replaced or the Paw control valve diaphragm of the existing Patient Circuit is changed. The control is necessary because the individual elastic and dimensional characteristics of the Paw control valve diaphragm interact with the valve control line pressure to determine the control dial maximum setting.

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CAUTION Do not overturn the Patient Circuit Calibration as this may cause damage to the device. When it is nearing its adjustment limit, it will reach a mechanical stop. The range, resolution, and accuracy of the pneumatic controls and the characteristics of the various pneumatic connections are described in Appendix B Specifications. Chapter 3 Controls, Displays and Connections provides a detailed description of the functions and use of each control.

WARNING Do not attempt to substitute another circuit configuration as this could result in injury to the patient and/or the operator, or cause equipment malfunction. The Patient Circuit described in this manual is specifically designed for patient use with the Model 3100A HFOV.

The Patient Circuit The Patient Circuit combines the three elements necessary for ventilation of the patient using HFOV techniques: •

bias flow/pressure,

•

pressure oscillations, and

•

pressure limiting.

The Patient Circuit is illustrated here in Figure 1.3 and shown schematically in Figure 1.1.

Figure 1.3. Details of Patient Circuit.

During normal operation, humidified, blended bias gas flows into the bias flow tube from the external humidifier. This gas flows into and through the inspiratory limb of the Patient Circuit, through the “Y” coupler and then into the expiratory limb of the Patient Circuit. While passing through the “Y” coupler, the fresh gas exchanges oxygen and carbon dioxide at the ET tube/patient connection.

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A proximal airway pressure sensing line made of 1/8" PVC tubing runs from the “Y” coupler to the Airway Pressure Monitor via a white Luer bulkhead fitting near the Patient Circuit connection. The pressure signal is processed to determine various pressure measurements and alarm conditions. The Airway Pressure Monitor and tubing are discussed in a following section. The expiratory limb carries the exchanged gas to the Paw Control Valve. This valve allows two expiratory flow paths. One path is a variable restriction controlled by the Paw Control Valve control line extending from the Pneumatic Logic and Control Subsystem via a green Luer bulkhead fitting near the Patient Circuit connection. The other flow path is a fixed orifice that requires a minimum bias flow be maintained through the Patient Circuit to ensure a flow of fresh Bias Gas regardless of the setting of the Paw Control Valve. When the Paw Control Valve is adjusted, it adjusts the mean airway pressure at the ET tube/patient connection after about five system time constants have elapsed, but only if the set bias flow and oscillator characteristics remain unchanged for the same time period. Five time constants can vary from about one second to as long as 30 seconds. This time constant varies directly with Paw and inversely with bias flow. The individual elastic and dimensional characteristics of the Paw Control Valve diaphragm interact with the valve control line pressure to determine the control dial maximum setting. The Patient Circuit Calibration adjustment control sets the maximum mean pressure that can be attained with a particular Patient Circuit under specified conditions. This control is used only when the Patient Circuit is replaced or the Paw control valve diaphragm of the existing Patient Circuit is changed. Refer to Chapter 6, Maintenance and Troubleshooting, for the complete setup procedure. The Pressure Limit Valve limits the Paw . When an abnormal condition exists or when the system mean pressure increases due to an inadvertent or deliberate control setting change, this valve acts to limit the mean proximal airway pressure. Both the Paw Control Valve and the Pressure Limit Valve are mushroom valves that must be replaced periodically. See Chapter 6, Maintenance and Troubleshooting for replacement instructions. The Dump Valve is activated by Electronic and Pneumatic Controls only when the following safety alarms are activated: 1.

Paw > 50 cmH2O

2.

Paw < 20% of “Set Max Paw ”

The Dump Valve, when activated, opens the Patient Circuit to ambient air. When the safety alarms have been activated, this allows the patient to breathe spontaneously at normal atmospheric pressure. In an emergency situation, the Dump Valve helps to prevent a decrease in cardiac output due to sustained elevated Patient Circuit pressure or atelectasis due to a negative Patient Circuit pressure. The Dump Valve is a mushroom valve that must be replaced at regular intervals as described in Chapter 6. Two ports are provided for inserting the temperature probe of the External Humidifier. One is near the patient “Y”; the other is near the Pressure Limit Valve. The inspiratory limb acts as the propagation means for the pressure oscillations generated by the Oscillator. A typical airway pressure oscillatory waveform is illustrated in Figure 1.4.

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