Check Valves and Manufacturer-Recommended Leak Test

1. Check Valves and Manufacturer-Recommended Leak Test

2. Low-Pressure Circuit Leak Test The low-pressure leak test checks the integrity of the anesthesia machine from the flow control valves to the common gas outlet. It evaluates the portion of the machine that is downstream from all safety devices except the oxygen analyzer. The components located within this area are precisely the ones most subject to breakage and leaks. Leaks in the low-pressure circuit can cause hypoxia and/or patient awareness. Flow tubes, the most delicate pneumatic component of the machine, can crack or break. A typical three-gas anesthesia machine has 16 O-rings in the low-pressure circuit.

3. Cont Leaks can occur at the interface between the glass flow tubes and the manifold and at the O-ring junctions between the vaporizer and its manifold. Loose filler caps on vaporizers are a common source of leaks, and these leaks can cause patient awareness under anesthesia. Several different methods have been used to check the low-pressure circuit for leaks, including the oxygen flush test, the common gas outlet occlusion test, the traditional positive-pressure leak test. The check valve is located downstream from the vaporizers and upstream from the oxygen flush valve. It is open in the absence of backpressure. Gas flow from the manifold moves the rubber flapper valve off its seat and allows gas to proceed freely to the common outlet.

4. Cont The valve closes when backpressure is exerted on it. Backpressure sufficient to close the check valve may occur with the following conditions: 1) oxygen flushing, 2) peak breathing circuit pressures generated during positive-pressure ventilation, 3)use of a positive-pressure leak test. Generally , the low-pressure circuit of anesthesia workstations without an outlet check valve can be tested with a positive-pressure leak test, and machines with check valves must be tested with a negative-pressure leak test.

5. Positive& Negative-Pressure Leak Test When performing a positive-pressure leak test, the operator generates positive pressure in the low-pressure circuit by using flow from the anesthesia machine or from a positive-pressure bulb to detect a leak. When performing a negative-pressure leak test, the operator creates negative pressure in the low-pressure circuit by using a suction bulb to detect leaks.

6. Inappropriate use of the oxygen flush valve to check the low-pressure circuit of an Ohmeda machine equipped with a check valve. The area within the rectangle is not checked by inappropriate use of the oxygen flush valve. The components located within this area are precisely the ones most subject to breakage and leaks. Positive pressure within the patient circuit closes the check valve, and the value on the airway pressure gauge does not decline despite leaks in the low-pressure circuit

7. Positive-Pressure Leak Test

8. 250 Liters

9. Pressure = 30 cmH2O

10. Negative-Pressure Leak Test  It is performed with a negative-pressure leak-testing device, which is a simple suction bulb. The machine's master switch, flow control valves, and vaporizers are turned off. The suction bulb is attached to the common fresh gas outlet and squeezed repeatedly until it is fully collapsed. This action creates a vacuum in the low-pressure circuitry. The machine is free of leaks if the hand bulb remains collapsed for at least 10 seconds. A leak is present if the bulb reinflates during this period. The test is repeated with each vaporizer individually turned to the “on” position because internal vaporizer leaks can be detected only with the vaporizer turned on.

11. Negative-Pressure Leak Test

12. Food and Drug Administration negative-pressure leak test. Left, A negative-pressure leak-testing device is attached directly to the machine outlet. Squeezing the bulb creates a vacuum in the low-pressure circuit and opens the check valve. Right, When a leak is present in the low-pressure circuit, room air is entrained through the leak and the suction bulb inflates.  

13. Negative-Pressure Leak Test If the bulb reinflates in less than 10 seconds, a leak is present somewhere in the low-pressure circuit. Therefore, it differentiates between breathing circuit leaks and leaks in the low-pressure circuit. The “universal” negative-pressure leak test is the most sensitive of all contemporary leak tests because it is not dependent on volume. That is, it does not involve the use of a breathing bag or corrugated hoses whose compliance could mask a significant leak. It can detect leaks as small as 30 mL/min. Finally, the operator does not need detailed or in-depth knowledge of proprietary design differences. If the operator performs the universal test correctly, the leak will be detected

14. Circle System Tests The circle system tests evaluate the integrity of the circle breathing system, which spans from the common gas outlet to the Y-piece . It has two parts—the leak test and the flow test. To thoroughly check the circle system for leaks, valve integrity, and obstruction, both tests must be performed preoperatively. The leak testis performed by closing the pop-off valve, occluding the Y-piece, and pressurizing the circuit to 30 cm H2O with the oxygen flush valve. The value on the pressure gauge will not decline if the circle system is leak free, but this does not ensure valve integrity. The value on the gauge will read 30 cm H2O even if the unidirectional valves are stuck shut or the valves are incompetent.

15. Cont The flow testchecks the integrity of the unidirectional valves, and it detects obstruction in the circle system. It can be performed by removing the Y-piece from the circle system and breathing through the two corrugated hoses individually. The valves should be present, and they should move appropriately. The operator should be able to inhale but not exhale through the inspiratory limb and able to exhale but not inhale through the expiratory limb. The flow test can also be performed by using the ventilator and a breathing bag attached to the “Y”-piece.

16. Workstation Self-Tests As mentioned previously, many new anesthesia workstations now incorporate technology that allows the machine to either automatically or manually walk the user through a series of self-tests to check for functionality of the electronic, mechanical, and pneumatic components. Tested components commonly include the gas supply system, flow control valves, circle system, ventilator, and, in the case of the Datex-Ohmeda Anesthesia Delivery Unit (ADU), even the Aladin cassette vaporizer. One particularly important point of caution with self-tests should be noted on systems with manifold-mounted vaporizers such as the Dräger Medical Fabius GS and the Narkomed 6000 series. A manifold-mounted vaporizer does not become part of an anesthesia workstation's gas flow stream until its concentration control dial is turned to the “on” position. Therefore, to detect internal vaporizer leaks on this type of system, the “leak test” portion of the self-diagnostic must be repeated separately with each individual vaporizer turned to the “on” position. If this precaution is not taken, large leaks that could potentially result in patient awareness, such as from a loose filler cap or cracked fill indicator, could go undetected.

17. Low-Pressure System Check Initial Status of Low-Pressure System:    a.    Close the flow control valves and turn the vaporizers off.     b.    Check the fill level and tighten the vaporizers’ filler caps.    Perform Leak Check of Machine Low-Pressure System:    a.    Verify that the machine master switch and flow control valves are OFF.    b.    Attach a “suction bulb” to the common (fresh) gas outlet.    c.    Squeeze the bulb repeatedly until it is fully collapsed.    d.    Verify that the bulb stays fully collapsed for at least 10 seconds.     e.    Open one vaporizer at a time and repeat steps c and d as above.     f.     Remove the suction bulb and reconnect the fresh gas hose.    Turn on Machine Master Switch and All Other Necessary Electrical Equipment.    Test Flow Meter :    a.    Adjust the flow of all gases through their full range while checking for smooth operation of the floats and undamaged flow tubes.     b.    Attempt to create a hypoxic O2/N2O mixture and verify correct changes in flow and/or alarm.

18. Scavenging System Adjust and Check Scavenging System:    a.    Ensure proper connections between the scavenging system and both the APL (pop-off) valve and ventilator relief valve.     b.    Adjust the waste gas vacuum (if possible).    c.    Fully open the APL valve and occlude the Y-piece.    d.    With minimum O2 flow, allow the scavenger reservoir bag to collapse completely and verify that the absorber pressure gauge reads about zero.     e.    With the O2 flush activated, allow the scavenger reservoir bag to distend fully and then verify that absorber pressure gauge reads less than 10 cm H2O.

19. Breathing System Calibrate O2 Monitor:     a.    Ensure that the monitor reads 21% in room air.    b.    Verify that the low-O2 alarm is enabled and functioning.    c.    Reinstall the sensor in the circuit and flush the breathing system with O2.     d.    Verify that the monitor now reads greater than 90%. .  Check Initial Status of Breathing System:    a.    Set the selector switch to “Bag” mode.    b.    Check that the breathing circuit is complete, undamaged, and unobstructed.     c.    Verify that CO2 absorbent is adequate.    d.    Install the breathing circuit accessory equipment (e.g., humidifier, positive end-expiratory pressure [PEEP] valve) to be used during the procedure. .  Perform Leak Check of Breathing System:    a.    Set all gas flows to zero (or minimum).    b.    Close the APL (pop-off) valve and occlude the Y-piece.     c.    Pressurize the breathing system to about 30 cm H2O with an O2 flush.   d.    Ensure that the pressure remains fixed for at least 10 seconds.     e.    Open the APL (pop-off) valve and ensure that the pressure decreases.

20. Manual and Automatic Ventilation Systems Test Ventilation Systems and Unidirectional Valves:     a.    Place a second breathing bag on the Y-piece.    b.    Set the appropriate ventilator parameters for the next patient.    c.    Switch to automatic ventilation (Ventilator) mode.     d.    Turn the ventilator ON and fill the bellows and breathing bag with an O2 flush.    e.    Set O2 flow to minimum and other gas flows to zero.    f.     Verify that during inspiration the bellows delivers appropriate tidal volume and that during expiration the bellows fills completely.    g.    Set the fresh gas flow to about 5 L/min.     h.    Verify that the ventilator bellows and simulated lungs fill and empty appropriately without sustained pressure at end expiration.    i.     Check for proper action of the unidirectional valves.    j.     Check the breathing circuit accessories to ensure proper function.    k.    Turn the ventilator OFF and switch to manual ventilation (Bag/APL) mode.     l.     Ventilate manually and ensure inflation and deflation of the artificial lungs and appropriate feel of system resistance and compliance.     m.    Remove the second breathing bag from the Y-piece.

21. Monitors Check, Calibrate, and/or Set Alarm Limits of All Monitors:    a.    Capnometer    b.    Oxygen analyzer     c.    Pressure monitor with high– and low–airway pressure alarms    d.    Pulse oximeter     e.    Respiratory volume monitor (spirometer)

22. Final Position Check Final Status of Machine:     a.    Vaporizers off     b.    APL valve open    c.    Selector switch to “Bag”     d.    All flowmeters to zero (or minimum)     e.    Patient suction level adequate     f.     Breathing system ready to use

23. Summary of Checkout Recommendations Item 1: Verify that the auxiliary oxygen cylinder and self-inflating manual ventilation device are available and functioning Item 2: Verify that patient suction is adequate to clear the airway Item 3: Turn on the anesthesia delivery system and confirm that AC power is available Item 4: Verify the availability of required monitors, including alarms Item 5: Verify that pressure is adequate on the spare oxygen cylinder mounted on the anesthesia machine Item 6: Verify that piped gas pressures are ≥50 psig Item 7: Verify that vaporizers are adequately filled and, if applicable, that filler ports are tightly closed Item 8: Verify that there are no leaks in the gas supply lines between the flow meters and the common gas outlet Item 9: Test scavenging system function Item 10: Calibrate or verify calibration of the oxygen monitor and check the low-oxygen alarm Item 11: Verify that the carbon dioxide absorbent is not exhausted Item 12: Check for proper breathing system pressure and leaks Item 13: Verify that gas flows properly through the breathing circuit during both inspiration and exhalation Item 14: Document completion of checkout procedures Item 15: Confirm ventilator settings and evaluate readiness to deliver anesthesia care (ANESTHESIA TIME-OUT)

24. Completed before Each Procedure Item 2: Verify that patient suction is adequate to clear the airway Item 4: Verify the availability of required monitors, including alarms Item 7: Verify that vaporizers are adequately filled and, if applicable, that filler ports are tightly closed Item 11: Verify that the carbon dioxide absorbent is not exhausted Item 12: Check for proper breathing system pressure and leaks Item 13: Verify that gas flows properly through the breathing circuit during both inspiration and exhalation Item 14: Document completion of checkout procedures Item 15: Confirm ventilator settings and evaluate readiness to deliver anesthesia care (ANESTHESIA TIME-OUT)