Anesthesia machine

Questions and Answers

What is the maximum safe ratio of N2O to O2 when using a proportioning device?

2:1 N2O to O2

3:1 N2O to O2 (correct)

4:1 N2O to O2

5:1 N2O to O2

What is the purpose of a hypoxia prevention device?

To provide oxygen to the user

To prevent setting a hypoxic mixture with the flow control valves (correct)

To monitor oxygen levels in the air

To regulate the flow of volatiles

What is the oxygen pressure failure device?

A device that increases oxygen flow if nitrogen oxide levels rise

A failsafe device that will shut off or proportionately reduce N2O flow if O2 pressure drops below 20 psi (correct)

A device that monitors oxygen levels in the atmosphere

A device that converts oxygen to nitrogen oxide

When will the hypoxic prevention safety device not alarm?

During pipeline cross over Signup and view all the answers

What is the main difference between an oxygen pressure failure device and a hypoxia prevention safety device?

OPFD (fail safe) shut off/reduce N2O supply if O2 pressure is below 20 psi, while HPSD (proportioning device) prevents hypoxic mixture of N2O and O2 Signup and view all the answers

How does the Link 25 proportioning system work? (select 2)

It automatically increases the O2 flow when you adjust the N2O flow in a way that would create a hypoxic mixture Signup and view all the answers

What are the pressure and boundaries of the high pressure system? (select 2)

O2 and N2O cylinders to cylinder regulators Signup and view all the answers

What is the pipeline pressure?

50 psi Signup and view all the answers

What is the pressure of the air from the cylinders (high pressure system) after the pressure regulator?

45 psi Signup and view all the answers

What are the boundaries of an intermediate-pressure system?

Pipeline to flow meter valves Signup and view all the answers

Where is the DISS used?

Pipeline Signup and view all the answers

Where is the pin-indexed safety system used?

Cylinders, hanger yoke assembly Signup and view all the answers

What are the boundaries of the low pressure system in an anesthesia machine?

flow meter to the common gas outlet Signup and view all the answers

What is composed of the low-pressure system?

Flowmeter tubes, vaporizers, and common gas outlet Signup and view all the answers

What is the pressure of the low-pressure system in an anesthesia machine?

Slightly above atmospheric pressure Signup and view all the answers

What system contains the failsafe device, O2 flush valve, flowmeter valve, O2 supply failure alarm, and pneumatic master switch?

Intermediate pressure system Signup and view all the answers

What is the function of the flowmeter valve?

To regulate the flow of each gas into the flowmeter Signup and view all the answers

How do you perform a low-pressure leak test (negative pressure test) on an anesthesia machine?

Attach bulb to common gas outlet and create negative pressure Signup and view all the answers

What is a passed negative pressure leak test indicated by?

Bulb stays sucked in after you create negative pressure (-65cmH2O) Signup and view all the answers

What should be done with the vaporizers during a negative pressure leak test?

Turn all vaporizers off, then test each individually Signup and view all the answers

How do you perform a positive pressure (high pressure) leak test on an anesthesia machine?

Place APL to 30-40, push flush valve and occlude pt elbow, bag should inflate without pressure drop Signup and view all the answers

What is the primary purpose of the positive pressure leak test on an anesthesia machine?

To verify the machine's ability to generate a positive pressure to ventilate a patient Signup and view all the answers

When a leak is present in the low-pressure circuit, what happens to the suction bulb during a negative pressure test?

It inflates due to entrainment of room air Signup and view all the answers

During spontaneous breathing, what is the position of the APL valve?

APL fully open Signup and view all the answers

During manual bag ventilation, what is the position of the APL valve?

Partially closed Signup and view all the answers

What is the consequence of too high or too low APL valve settings in bag ventilation?

Too high: barotrauma, Too low: ineffective pressure to generate inspiration Signup and view all the answers

What is the position of the APL valve during mechanical ventilation?

Closed Signup and view all the answers

During mechanical ventilation, the bellows serve as the?

reservoir bag Signup and view all the answers

What is the position of the bellows during inspiration and expiration?

Descends during inspiration and ascends during expiration Signup and view all the answers

The vent outflow valve is the same as the ___

pop-off valve/ APL Signup and view all the answers

What is the purpose of the APL and vent outflow valve?

To release excess gas Signup and view all the answers

Modern vaporizers are outside of the circle system

True Signup and view all the answers

Why does desflurane require a special vaporizer?

It's vapor pressure (660) is close to atmospheric pressure (760) Signup and view all the answers

What is the purpose of the variable bypass vaporizer?

To provide a constant concentration of anesthetic vapor by splitting the flow between the vaporizer chamber flow and bypass flow Signup and view all the answers

What is the purpose of the temperature compensating valve?

To adjust for the heat lost by vaporized molecules Signup and view all the answers

Where does fresh gas flow that does not come in contact with volatile agents in the vaporizer?

Through the bypass pathway Signup and view all the answers

What is the definition of the splitting ratio in an anesthesia machine?

The ratio of fresh gas flow that goes through the vaporizing chamber to fresh gas flow that goes through the bypass pathway Signup and view all the answers

What happens to the output concentration of the vaporizer when the temperature of the liquid agent drops?

It drops Signup and view all the answers

Vapor pressure is directly proportional to ___

temperature Signup and view all the answers

What is the effect of changing pressure affecting the output of the vaporiser called?

Pumping effect Signup and view all the answers

During PPV, where is the pressure transmitted?

to both the bypass channel and the vaporizer chamber Signup and view all the answers

Where does the increased flow of backpressure travel to during positive pressure ventilation (PPV)?

Vaporizer chamber, resulting in compression of fresh gas Signup and view all the answers

When the positive pressure is released during PPV (i.e. exhalation), what is the result of the rapid expansion of compressed gas in the vaporizer chamber?

Vaporized gas travels to the bypass chamber, increasing the concentration of inhaled anesthetic Signup and view all the answers

What is the end result of the pumping effect in an anesthesia machine?

increased delivered concentration of volatile anesthetic Signup and view all the answers

What is the result of tipping of the vaporizer?

Increased vaporizer output Signup and view all the answers

When can a leak in the vaporizer be identified?

When the vaporizer is turned on Signup and view all the answers

How does a TEC 6 desflurane vaporizer work?

By heating/pressuring and injecting a precise amount of vaporized desflurane into the fresh gas flow Signup and view all the answers

What is the effect of higher ambient pressure (hyperbaric oxygen tank) on the desflurane vaporizer?

Lower concentrations Signup and view all the answers

What is the result of a lower ambient pressure (higher altitude) when using desflurane?

A higher delivered concentration Signup and view all the answers

Why must desflurane be heated and pressurized to 39°C and 2 atm?

Due to its lower potency, a greater volume of desflurane has to be vaporized to achieve anesthesia Signup and view all the answers

What is the purpose of the oxygen alternate flowmeter?

To bypass the digital flowmeter in the event of a malfunction Signup and view all the answers

The master switch is normally linked to the ____ switch

Pneumatic Signup and view all the answers

In the intermediate system, what is the purpose of the pipeline pressure (50) being higher than the cylinder pressure (45)?

To prioritize gas flow from the pipeline rather than the cylinder Signup and view all the answers

The O2 flush valve and auxiliary O2 are not controlled by the master switch

True Signup and view all the answers

Why is oxygen used as a driving gas in the bellows?

In the event of a leak in the bellows, O2 is safe for the pt Signup and view all the answers

How does the failsafe work in the intermediate system?

It pushes the lever up to allow the flow of N2O if adequate O2 is present (20 psi). Signup and view all the answers

What is a Thorpe tube?

Variable orifice flowmeter Signup and view all the answers

Higher flow rates tend to be which type of flow?

turbulent Signup and view all the answers

What is the ideal position of oxygen in a flowmeter?

Closest to the patient Signup and view all the answers

What can alert you to the presence of a leak in the flowmeter?

FIO2 less than what you've set it to Signup and view all the answers

What can cause retrograde flow in an anesthesia machine?

Increased patient pressure, such as during coughing Signup and view all the answers

What is the typical flow rate of the flush valve on an anesthesia machine?

50-70 L/min Signup and view all the answers

What is the typical pressure range of a flush valve?

45-50 psi Signup and view all the answers

Pushing the O2 flush valve while the patient is breathing spontaneously can result in what?

Diluting the anesthetic gases Signup and view all the answers

What are the three most important preoperative checks on an anesthesia machine?

Calibration of the O2 analyzer, low pressure circuit leak test, and circle system tests Signup and view all the answers

How do you calibrate the oxygen analyzer?

Open it to room air Signup and view all the answers

What can you conclude about the integrity of the system from the flowmeter assembly to the breathing circuit if you have pressure tested your breathing system by closing the adjustable pressure limiting (APL) valve and manually occluding the Y-connector while flushing the circuit with oxygen?

Nothing because the check valve stops you from checking the flowmeters (one-way flow) Signup and view all the answers

What does the positive pressure leak test primarily test in an anesthesia machine?

Only the circle system Signup and view all the answers

When would you want to use transtracheal jet ventilation?

When chest movement needs to be decreased Signup and view all the answers

Where is the oxygen analyzer typically located, and what is its primary purpose?

In the inspiratory limb, as a final defense against delivery of a hypoxic mixture Signup and view all the answers

How does the piston ventilator work?

It uses an electric motor to compress bellows and generate pressure Signup and view all the answers

What are the advantages of piston bellows?

Both a and b Signup and view all the answers

How do piston ventilators deliver a constant tidal volume?

By decoupling free gas flow from the ventilator Signup and view all the answers

What is the consequence of coupling of VT to fresh gas flow in pneumatic bellows ventilators?

Changes to fresh gas flow will affect the VT Signup and view all the answers

What is the frequency of the positive pressure leak test?

Before each anesthetic procedure Signup and view all the answers

What is the frequency of the negative pressure leak test?

Daily Signup and view all the answers

Study Notes

Anesthesia Machine Components and Functions

The maximum safe ratio of N2O to O2 when using a proportioning device is 3:1 or less.
A hypoxia prevention device prevents accidental delivery of a hypoxic gas mixture.

Hypoxia Prevention Devices

A hypoxia prevention safety device will not alarm when the oxygen pressure is above a minimum threshold.
The main difference between an oxygen pressure failure device and a hypoxia prevention safety device is that the former alarms when oxygen pressure drops below a set point, while the latter alarms when the oxygen percentage in the mixed gas falls below a set point.

Link 25 Proportioning System

The Link 25 proportioning system works by sensing the oxygen pressure and adjusting the nitrous oxide flow accordingly to maintain a safe ratio.

High-Pressure System

The pressure boundaries of the high-pressure system are between 400 and 1370 psi.
The pipeline pressure is typically 50 psi.
The pressure of air from the cylinders after the pressure regulator is typically 45 psi.

Low-Pressure System

The boundaries of the low-pressure system in a hypoxia prevention device are between 10 and 14 psi.
The low-pressure system in an anesthesia machine includes the flowmeter valve, O2 supply failure alarm, pneumatic master switch, and failsafe device.
The pressure of the low-pressure system in an anesthesia machine is typically around 10-14 psi.

Failsafe Device and Oxygen Flush Valve

The failsafe device, O2 flush valve, flowmeter valve, O2 supply failure alarm, and pneumatic master switch are all part of the low-pressure system.
The function of the flowmeter valve is to regulate gas flow to the patient.

Leak Testing

A low-pressure leak test (negative pressure test) is performed on an anesthesia machine to detect leaks in the low-pressure circuit.
A passed negative pressure leak test is indicated by the suction bulb remaining collapsed.
During a negative pressure leak test, the vaporizers should be turned off.
A positive pressure leak test (high-pressure leak test) is performed to detect leaks in the high-pressure circuit.
The primary purpose of the positive pressure leak test is to detect leaks in the high-pressure circuit.

APL Valve and Vent Outflow Valve

During spontaneous breathing, the APL valve is open.
During manual bag ventilation, the APL valve is closed.
The consequence of too high or too low APL valve settings in bag ventilation is inadequate ventilation.
During mechanical ventilation, the APL valve is closed.
The APL valve and vent outflow valve serve to vent excess gas from the breathing circuit.

Vaporizers

Modern vaporizers are outside of the circle system.
Desflurane requires a special vaporizer that is heated and pressurized to 39°C and 2 atm.
The purpose of the variable bypass vaporizer is to maintain a consistent output concentration despite changes in temperature or pressure.
The purpose of the temperature compensating valve is to adjust the vaporizer output concentration based on temperature changes.

Anesthesia Machine Operation

The splitting ratio in an anesthesia machine is the proportion of fresh gas that flows through the vaporizer versus that which bypasses it.
The output concentration of the vaporizer increases when the temperature of the liquid agent drops.
Vapor pressure is directly proportional to temperature.
The effect of changing pressure affecting the output of the vaporizer is called the pumping effect.

Pressure and Flow

During PPV, pressure is transmitted to the breathing circuit.
The increased flow of backpressure travels to the vaporizer chamber during PPV.
When the positive pressure is released during PPV, the result is a rapid expansion of compressed gas in the vaporizer chamber.
The end result of the pumping effect is an increased output concentration of the vaporizer.

Desflurane Vaporizer

The TEC 6 desflurane vaporizer works by heating and pressurizing the desflurane to 39°C and 2 atm.
The effect of higher ambient pressure on the desflurane vaporizer is an increased output concentration.
The result of a lower ambient pressure when using desflurane is a decreased output concentration.
Desflurane must be heated and pressurized to 39°C and 2 atm to achieve a consistent output concentration.

Miscellaneous

The oxygen alternate flowmeter is used to measure oxygen flow separately from other gases.
The master switch is normally linked to the O2 flush valve switch.
Pipeline pressure (50) is higher than cylinder pressure (45) to ensure a reliable supply of oxygen to the anesthesia machine.
Oxygen is used as a driving gas in the bellows because it is safer and more efficient.
The failsafe device in the intermediate system shuts off the machine in case of failure.

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