anesthesia machine leaks

1. 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.

2. 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.

3. 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.

4. 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.

5. 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

6. Positive-Pressure Leak Test

7. 250 Liters

8. Pressure = 30 cmH2O

9. 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.

10. Negative-Pressure Leak Test

11. 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.

12. 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

13. 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 test is 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.

14. Cont
• The flow test checks 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.

15. 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.

16. 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.

17. 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.