Anesthesia Machine
What does the American Society for Testing and Materials (ASTM) do?
Sets the standards for the required components of the anesthesia machine.
What does the Food and Drug Administration (FDA) do?
Developed the anesthesia machine pre-use checkout procedures.
What does the Occupational Safety and Health Administration (OSHA) do?
Sets the standards for acceptable occupational exposure to volatile anesthetics.
What does the Department of Transportation (DOT) do?
Sets the requirements for compressed gas cylinders.
Oxygen pressure FAILURE
- Monitors oxygen pressure (not concentration).
- Activates when oxygen pressure in the intermediate pressure system falls below 20 psi.
- NOT activated by a pipeline crossover or if a leak develops distal to the flowmeters.
Oxygen analyzer (NOT oxygen pressure failure device)
Oxygen analyzer monitors oxygen concentration in the low-pressure system. It alarms when the FiO2 falls below 21%.
Oxygen Pressure Failure Device (Failsafe)
Resides in the intermediate-pressure system
- Monitor for (and protect against) low oxygen pressure in the anesthesia machine.
- Will alert you about depleted oxygen tank, a drop in pipeline pressure, or a disconnected oxygen hose.
- Consists of 2 components:
1. A threshold alarm that sounds when the oxygen pipeline pressure falls below 28-30 psi.
2. A pneumatic device that reduces or stops the flow of nitrous oxide when the pressure in the oxygen pipeline falls below 20 psi.
What is a unique characteristic of oxygen in the anesthesia machine?
- Oxygen is the ONLY gas that passes directly from its source to its flow valve at the flowmeter.
- All the other gases must first encounter a fail-safe valve before it enters its flowmeter.
- For sake of completeness, we should mention that some newer machines do not require air to pass through a failsafe valve.
- This allows the patient to be ventilated with air if an oxygen supply is not available.
Which monitor will be the FIRST to detect an oxygen-pipeline crossover?
- The oxygen analyzer measures O2 concentration INSIDE the breathing circuit, making it the only safety device on the anesthesia machine that will alert you to an oxygen-pipeline crossover.
- The SpO2 would be a later indicator.
- Keep in mind that hypoxemia has many causes, and a pipeline crossover is likely pretty far down on your differential.
- The FAILSAFE DEVICE and HYPOXIA PREVENTION SAFETY DEVICES help to prevent a hypoxic mixture, however, neither monitor oxygen concentration.
Which components of the anesthesia machine could be affected if the low-pressure leak test fails?
The low-pressure leak test (negative pressure test) assesses the low-pressure circuit’s integrity from the flowmeter valves to the common gas outlet. It does NOT assess any part of the breathing circuit.
The anesthesia machine can be divided into 3 systems based on the pressure in each:
- HIGH PRESSURE system - Back up cylinders, cylinder yoke, cylinder gauge, and cylinder regulator.
- INTERMEDIATE pressure system - Pipeline inlets, check valves, pressuge gauges, ventilator power inlet, oxygen pressure system, flowmeter control valve, oxygen 2nd stage regulator, and oxygen flush valve.
- LOW PRESSURE system - Flowmeter tubes, vaporizers, common gas outlet, and check valves if present.
Low pressure circuit leak test checks…
- The integrity of the machine from the flow control vales to the common gas outlet.
- BEST METHOD to detect vaporizer leak.
- The low pressure circuit test is conducted by attaching a bulb to the common gas outlet and creating a negative pressure in the low pressure system. Specifically it tests for a leak between the flow control valves to the common gas outlet.
- The low pressure circuit leak test does NOT include the anesthesia circuit, whihc is beyond the common gas outlet.
OXYGEN FLUSH VALVE
- Delivers a flow rate between 35-75 L/min.
- Provides a direct link between the oxygen pipeline (50 psi) and the breathing circuit.
- The oxygen flush valve BYPASSES the flowmeters and the manifold.
What ISSUES can the oxygen flush valve create?
- Because the ventilator spill valve is closed during inspiration, pressing the O2 flush valve during the inspiratory phase exposes the breathing circuit to pipeline pressure. This increases the risk of barotrauma.
- Adding a large quantity of oxygen to the breathing circuit dilutes anesthetic vapors. This can increase the risk of awareness.
OXYGEN E-CYLINDER
Maximum service pressure
2000
BREATHING SYSTEM
Classifications
- OPEN: No rebreathing and no reservoir.
- SEMI-OPEN: No rebreathing with a reservoir.
- SEMI-CLOSED: Partial rebreathing with a reservoir.
- CLOSED: Complete rebreathing with a reservoir.
BREATHING CIRCUITS
