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Checkout Procedures of Anesthesia Apparatus
These checkout procedures are intended for anesthesia machines without self-checking mechanisms. For anesthesia machines with self-checking mechanisms, follow the manufacturer’s instructions. However, some anesthesia machines cannot detect circuit obstruction. Before using such machines, open the breathing circuit and confirm that the pressure inside the circuit returns to 0 cmH2O. When self-checking procedure has been done before assembling anesthesia circuit completely (i.e. attaching a heat and moisture exchanger, an angle piece, a gas sampling tube, and sensors, etc.), reconfirm that there is no circuit leak or circuit obstruction after attaching such attachments.
1. Auxiliary cylinders and flowmeters Explanation 1
- Open the auxiliary cylinder (oxygen) and confirm that the pressure is at least 5 MPa. If there is a nitrous oxide cylinder, then check its contents as well.
- Check the movement of the knob(s) and gas flow display.
- Confirm that oxygen is flowing at 5 L/min.
- If the machine has a fail-safe mechanism to prevent administration of hypoxic gases such as pure nitrous oxide, then check that it is operating properly.
2.Fail-safe mechanism and alarm in the event of auxiliary oxygen cylinder pressure loss Explanation 2
- Set the oxygen and nitrous oxide flows to 5 L/min.
- Close the oxygen cylinder and confirm that the alarm sounds and nitrous oxide is cut off (some devices may not have alarms).
- Return the oxygen flow to 5 L/min and confirm that the nitrous oxide flow automatically returns to 5 L/min. Turn off the nitrous oxide flow.
- Turn off the oxygen flow.
- Close the oxygen and nitrous oxide cylinders and confirm that the flowmeters return to 0.
3.Medical gas central pipeline supply Explanation 3,4
- When connecting the hose assemblies (e.g., oxygen, nitrous oxide, compressed air), perform a visual check for damage as well as leaks.
- Properly connect the hose assemblies to the medical gas outlets or medical gas piping and anesthetic gas scavenging system and then check the gas supply pressures. The oxygen supply pressure should be 392 ± 49 kPa (4 ± 0.5 kgf/cm2), whereas the nitrous oxide and compressed air pressures should be 30 kPa (about 0.3 kgf/cm2) lower than the oxygen supply pressure. Check the scavenging system’s suction pressure (≥1 kPa, < 2 kPa) and volume (≥ 25 L/min, ≤ 50 L/min; systems with flow adjustability can be adjusted from 0–30 L/min).
- Check the movement of the knob(s) and gas flow display.
- If the anesthesia machine has a fail-safe mechanism (to prevent the direct administration of pure nitrous oxide to patients), then check that it is operating properly.
- With oxygen and nitrous oxide flowing, check if the alarm sounds and nitrous oxide supply is cut off when the oxygen hose assembly is detached (some devices do not have alarms).
- In facilities without medical gas piping systems, check the main cylinder’s pressure and contents prior to use in the same way as performed for the auxiliary cylinders.
4.Vaporizers Explanation 5
- For vaporizers that require a power source, check that the power cable is connected and power is ON.
- Check the contents.
- Firmly close the injection valve.
- With the vaporizer OFF and oxygen flowing, confirm that there is no smell.
Check that the dial is operating smoothly. - Visually confirm that the connection is secure. If there are two or more vaporizers, confirm that multiple dials do not move simultaneously (i.e., two vaporizers may not operate at the same time).
5.Oxygen sensor
- For anesthesia machines that use an electro-galvanic oxygen sensor, check the date the sensor was opened. Alternatively, confirm the calibration check records.
- Expose the sensor to the atmosphere and calibrate it to 21%.
- Insert the sensor into the circuit and set the oxygen flow to 5–10 L/min. Confirm that the oxygen concentration rises to 100%.
6.Carbon dioxide absorbent
- Perform a visual check of the color, amount, uniformity, and other aspects of the absorbent.
- If there is a water drainage system, make sure to close it after draining.
7.Patient breathing circuit assembly Explanation 6
- Confirm that the circuit has been assembled correctly and securely.
8.Leak testing of the patient breathing circuit and anesthesia machine internal circuit, oxygen flush Explanation 7,8
- Set the fresh gas flow to 0 or the minimum level.
- Close the APL (pop-off) valve and block the patient breathing circuit end (Y piece).
- Set the oxygen flow to 5–10 L/min and inflate the breathing bag until the pressure inside the breathing circuit reaches 30 cmH2O. Next, squeeze the bag to raise the pressure inside the circuit to 40–50 cmH2O and check for leaks.
- Release the bag so that the pressure returns to 30 cmH2O. Stop the oxygen flow, wait for 30 seconds, and confirm that the drop in pressure is < 5 cmH2O.
- Open the APL valve and confirm that the pressure inside the circuit drops.
- Activate the oxygen flush valve and confirm that the flow is sufficient.
There is no set rule for leak testing, and procedures vary between devices. However, automated leak testing is preferred and should be used whenever available (option C). If the function is not available, use the manual method (option A).
9.Manual ventilation with the patient breathing circuit Explanation 9
Attach a test lung and set the oxygen or compressed air flow to 5–10 L/min. After inflating the breathing bag, press on it to check the movements of the inhalation and exhalation valves. Confirm that the test lung moves (i.e., inflates or deflates) accordingly. Other methods can be used that do not involve a test lung.
10.Ventilator and alarms
- Change the ventilation setting from manual to mechanical ventilation.
- Confirm movement of the test lung.
- Set the ventilator to volume-controlled ventilation, detach the test lung, and check the low-pressure alarm. Put pressure on the test lung or occlude the patient connection port on the breathing circuit to confirm that the high-pressure alarm is operational.
- Set the ventilator to pressure-controlled ventilation and occlude the breathing circuit or put pressure on the test lung to check the low minute ventilation or low tidal volume alarms.
11.Completion
- Confirm that all of the checks have been completed.
Explanations
Explanation 1 Auxiliary cylinders and flowmeters
It is important to always be prepared for the possibility that something will cause the gas supply from the medical gas piping system or main cylinder to suddenly stop. Self-inflating bags (e.g., Ambu bags) should be available for emergency use, and anesthesia machines should always be equipped with auxiliary cylinders of oxygen and nitrous oxide (or, at the very least, oxygen) that are available for immediate use. If it is difficult to place auxiliary cylinders on the anesthesia machine itself (e.g., on a ceiling pendant mount), then separate auxiliary cylinders need to be available for use. Before connecting the hose assemblies (e.g., oxygen, nitrous oxide) to the anesthesia machine, check the contents (pressures) and gas flow from the auxiliary cylinders. Note that these cylinders must be positioned upright.
- Open the auxiliary oxygen cylinder and check the pressure. When full, an oxygen cylinder has a maximum pressure of 14,710 kPa (150 kgf/cm2), which should decrease linearly with use. When the pressure falls below 5,000 kPa (50.9 kgf/cm2), the cylinder should be replaced.
- Turn on the oxygen flow and set to 5 L/min. Visually confirm a stable flow rate and that the cylinder pressure does not decline when oxygen is flowing.
- While maintaining the oxygen flow at 5 L/min, perform the same visual check for nitrous oxide. Open the nitrous oxide auxiliary cylinder. At 20 ℃, the pressure of a nitrous oxide cylinder is 5,099 kPa (52 kgf/cm2). Caution is needed because, unlike oxygen, nitrous oxide does not show a decrease in pressure until 80% of it has been consumed, after which the pressure declines rapidly. Replace the nitrous oxide cylinder if the pressure is below 5,099 kPa (52 kgf/cm2).
- Turn on the nitrous oxide flow and set to 5 L/min. Visually confirm a stable flow rate and that the cylinder pressure does not decline when nitrous oxide is flowing.
- If the flowmeter has a fail-safe device (to prevent the supply of pure nitrous oxide), then check that it is operating properly. Specifically, visually confirm that when the oxygen flow is gradually shut off, the nitrous oxide flow also starts to decline once the oxygen decreases below a certain amount. Typically, when the oxygen concentration decreases below 30%, the nitrous oxide flow will start to drop. Moreover, confirm that when the oxygen flow reaches 0, the flow of nitrous oxide is also 0.
Explanation 2 Fail-safe mechanism and alarm in the event of auxiliary oxygen cylinder pressure loss
Fail-safe mechanisms are installed in anesthesia machines to stop the supply of all other gases when oxygen supply pressure is low, in order to avoid delivery of mixed gas at a low oxygen concentration.
- After inspecting the auxiliary cylinders, perform the following procedures.
- Set the oxygen flow to 5 L/min, which will return the nitrous oxide flow to 5 L/min.
- Close the main valve of the auxiliary oxygen cylinder to cut off the supply of oxygen. Visually confirm a drop in cylinder pressure.
- Confirm that when the oxygen supply pressure goes below the anesthesia machine’s preset threshold, an alarm sounds and the supply of nitrous oxide is cut off. In addition, visually confirm that the nitrous oxide flow decreases as the oxygen flow declines. When the oxygen flow reaches 0, the flow of nitrous oxide also decreases to 0. In some machines, the nitrous oxide flow is immediately cut off when the oxygen flow decreases. However, use caution as some old devices may not have alarms.
- After finishing this inspection, close the main valve of the nitrous oxide cylinder and wait until the pressure decreases to 0. Following this, turn the knobs of the oxygen and nitrous oxide flowmeters to OFF. If gas is flowing when the hose assembly from the medical gas piping system is attached, then this could damage the flowmeter.
Explanation 3 Medical gas central pipeline supply
- First, attach the oxygen hose assembly of the medical gas piping system and visually confirm the oxygen supply pressure setting, which is normally 392 ± 49 kPa (4 ± 0.5 kgf/cm2).
- Turn on the oxygen flow and visually confirm a stable flow rate by the movement of the flowmeter. Turn the oxygen flow OFF.
- Visually confirm that the nitrous oxide flow does not rise, even when the nitrous oxide flow is enabled. Turn the nitrous oxide flow OFF.
- Next, attach the nitrous oxide hose assembly and visually confirm the nitrous oxide supply pressure setting, which is normally 30 kPa (0.3 kgf/cm2) lower than the oxygen setting.
- Turn on the oxygen flow and then turn on the nitrous oxide flow. Visually confirm a stable flow rate by the movement the flowmeter, then turn the flow OFF.
- For anesthesia machines with an air flowmeter, connect the compressed air hose assembly and visually confirm the air supply pressure, which is normally 30 kPa (0.3 kgf/cm2) lower than the oxygen pressure.
- Turn on the air flow and visually confirm a stable flow rate by the movement of the flowmeter. Turn the air flow OFF. (Normally, nitrous oxide and compressed air cannot be used simultaneously. The desired gas may be selected using a lever or separate device).
- Connect the anesthetic gas scavenging system and, with the valve open, confirm the suction pressure (≥ 1 kPa, < 2 kPa) and flow (≥ 25 L/min, ≤ 50 L/min; systems with flow adjustability can be adjusted from 0–30 L/min).
Note: In facilities without medical gas piping systems, check the main cylinder’s pressure and contents prior to use in the same way as performed for the auxiliary cylinders.
Explanation 4 Medical gas piping system
Medical gas piping systems are designed to supply medical gases to the point of care through piping from a separately installed high-pressure gas supply . A manifold or low temperature liquid gas container (LGC) may be used to supply high-pressure gas. The manifold combines multiple gas sources (banks), and typically has a left and right bank with a device for switching between the two. In some devices, an alarm sounds when one bank is depleted, and the gas supply is automatically switched to the other side. Gas supplied from cylinders or LGC are distributed to designated areas via pipes after passing through a pressure regulator.
The piping terminal (outlet) uses a pin index safety system or Schrader system to prevent misconnections. The tubes that connect the piping terminal (outlet) to the anesthesia equipment or other devices are called hose assemblies.
Explanation 5 Vaporizers
If another type of anesthetic is mistakenly injected into a vaporizer, the vaporizer can be used after the following procedures; remove the anesthetic from the vaporizer and evaporate the remaining fluid completely by sending a high fresh gas flow with the vaporizer set to maximum. The vaporizer should be overhauled by the manufacturer in the event of injection of fluid other than the specified anesthetic, as this could change the vaporizing efficiency.
Explanation 6 Patient breathing circuit assembly
Regarding connections
Most patient breathing circuits are assembled using conical connections with male and female ends, which are 15 or 22 mm in diameter, respectively. Although conical connections are easy to connect, they also disconnect easily. Disconnections and leaks are incredibly common in patient breathing circuits. Therefore, it is important to make sure to rotate the connections when inserting them and exercise caution when assembling and using circuits. The following areas have been problematic in the past; however, many other issues may occur.
・Plastic to plastic connections: disconnection
・Plastic to metal connections: plastic damage, abrasion
・Metal to metal connections: improper joining due to deformation, leaks
・Plastic to rubber connections: loss of elasticity, disconnection due to cracks, leaks
Explanation 7 Leak testing of the patient breathing circuit and anesthesia machine internal circuit
Pressure test methods
Generally, patient circuit leaks are identified by running oxygen gas through the circuit and applying pressure.
A. Manual method
Close the end of the patient breathing circuit (Y piece) and APL valve, set the oxygen flow to 5–10 L/min, and inflate a breathing bag to 30 cmH2O. Next, squeeze the breathing bag until the pressure inside the circuit reaches 40–50 cmH2O. If there is a large leak, it will be difficult to maintain the pressure level. If there is a loose connection, then it will disconnect, allowing for poor connections to be detected. Release the breathing bag and allow the pressure to return to 30 cmH2O. Stop the oxygen flow and wait 30 seconds with no gas supply to confirm that the drop in pressure is < 5 cmH2O. For anesthesia machines without a check valve in the low-pressure circuit system, the breathing bag may be inflated using an oxygen flush.
Note: For anesthesia machines with a common gas outlet check valve, leaks in the low-pressure circuit system cannot be detected using method A. Use method B as follows.
B. Low-pressure circuit system leak test
Close the APL valve and set the oxygen flow to about 100 mL/min. Remove the breathing bag and block the breathing bag port and Y piece with both hands or connect them together with another breathing hose. Check that the circuit’s internal pressure scale reaches at least 30 cmH2O. Before the pressure gets too high, set the oxygen flow to 0. This test can show that leaks from the needle valve to the breathing circuit are less than 100 mL/min at pressures up to 30 cmH2O. However, there may be internal leaks within the manufacturer’s specifications. Moreover, leaks in the breathing bag or between the bag and its port cannot be detected by method B only. To detect these leaks, method B must be combined with method A.
Tests at lower flow rates can be performed depending on the anesthesia machine flowmeter. For some machines, the minimum flow rate may be greater than 100 mL/min. Tests should be performed at the device’s minimum flow rate.
To check for leaks in and around the vaporizers, it is best to perform leak tests with each vaporizer switched on. To check for leaks between the flowmeter and common gas outlet, a negative pressure test must be performed if there is a check valve between them. The vaporizers also must be on to perform automated leak tests. Automated leak tests should be performed for each vaporizer. Therefore, when changing vaporizers, time needs to be allotted for testing.
Leak tests of the low-pressure circuit system of anesthesia machines should be performed during maintenance inspections by clinical engineers or regular inspections by the manufacturer.
Carbon dioxide absorption equipment
Leaks are most likely to occur in carbon dioxide absorption equipment. Loose screws, lost, damaged, or deteriorated gaskets, or loose absorbent granules can lead to incomplete seals and many other problems. Absorption equipment leaks can be detected using the pressure tests described above.
Explanation 8 Oxygen flush
- Check for lost or damaged buttons and levers.
- Confirm that the button or lever operates properly.
- Confirm that the mechanism resets properly.
- Confirm that oxygen flows properly.
- Confirm that the oxygen flow is sufficient. In a closed circuit, an oxygen flush at 35–75 L/min should inflate a 5 liter bag to 20 cmH2O in about 5 seconds.
Explanation 9 Manual ventilation with the patient breathing circuit
Test lung
A test lung is a self-deflating rubber bag or bellows that holds about 0.5–2 L and is used to check the settings and operation of the anesthesia machines.
Simple breathing resistance inspection
(1) Without a test lung
Close the APL valve and observe the movements of the inhalation and exhalation valves while lightly tapping the end of the Y piece with the palm of your hand.
(2) With a test lung
Attach the test lung and set the oxygen flow to 4–6 L/min. Ventilate the bag with the APL valve slightly open. During this process, the pressure inside the circuit should be 15–20 cmH2O. The inhalation and exhalation valves should move smoothly, and the test lung should inflate and deflate properly along with the bag’s movement.
Adjustable pressure limiting (APL) valve
Located near the breathing bag, the APL valve (or pop-off valve) is used to regulate the pressure inside the breathing circuit through the release of anesthetic gas. In most modern anesthesia machines, the APL valve is connected to the anesthetic gas scavenging system. Structurally, some APL valves regulate the opening pressure using a spring or a weight, and others regulate the pressure by changing the aperture size (resistance).
Inspection method
After confirming that there are no leaks in the breathing circuit, press on the end of the Y piece and set the oxygen flow to 4–6 L/min. After the pressure inside the circuit rises to about 30 cmH2O, fully open the APL valve and confirm an abrupt drop in pressure. Next, attach a test lung and repeatedly open and close the APL valve while squeezing the breathing bag to confirm the smooth variation in pressure inside the circuit.
References for English Version:
Guideline for developing institution-specific checkout procedures prior to anesthesia delivery (ASA2008)
Checking anaesthetic equipment 2012 (Anaesthesia 2012)
Modern anaesthetic machines (Continuing Education Anaesthesia, Critical Care & Pain: 6(2), 2006)
Japanese Version:
Enacted August 1990
Enacted July 1995
Enacted June 2003
Revised March 2013
Revised November 2014
Revised March 2016
Revised August 2019
English Version:
Enacted October 2019
Japanese Society of Anesthesiologists
