Parts of the Anesthetic Machine

A&A Pages 100-135

Purpose of the Anesthetic MachineA liquid inhalant anesthetic is vaporized into a carrier gas, and delivered to the patient via a breathing circuit.

Oxygen is delivered at a controlled rate Isoflurane is converted to a gas delivered through a breathing circuitGases exhaled from the patient are scavenged OR can be re-circulated (once CO2 has been removed)

*Can also be used to deliver just oxygen during recovery or in an emergency*

Components of the Anesthetic Machine

1. Compressed gas supply Gas tanks, their pressure gauges, pressure reducing valves,

line pressure gauge, flow meter, flush valve

2. Anesthetic vaporizer Precision, out-of-circuit vaporizer is ideal (what we use) Vaporizer inlet port and vaporizer outlet port

3. Breathing circuit Fresh gas inlet, unidirectional valves, breathing tubes,

reservoir bag, pop-off valve, CO2 canister, pressure manometer, negative pressure relief valve

4. Scavenging System Disposes of excess and waste anesthetic gases; consists of a

tube and the scavenger (multiple types)

PART 1: Compressed Gas Supply

Gas CylindersMost commonly used carrier gas is oxygen

Why?

It comes compressed in a metal cylinder and held under pressure- up to 2200 psi

Available in various sizes: “E” tanks hold 660 L of oxygen “H” tanks hold 6900 L of oxygen

Tanks are delivered and picked up by the oxygen supply company as needed

Gas CylindersTanks are color coded for safety and recognition

Oxygen tanks: ___________

Nitrous oxide tanks: _________

Carbon dioxide tanks: ________

E tanks/cylinders, attach to the anesthetic machine via a yoke.

H tanks/cylinders can be attached via hoses or pipes.

Gas lines may be used to bring the oxygen into the surgical area from another room.

Gas Cylinders- SafetyIn addition to color-coded tanks, the yokes are gas-specific.

The valve on the oxygen tank matches the connecter on the yoke specific to oxygen

An oxygen yoke has two pins below the outlet port

The yoke is connected to a pressure reducing valve to control the amount of gas released.

*May or may not be able to see this component*

Gas Cylinders- SafetyCombustible gases- avoid flames and sparks!

Tanks must be stored in a secure location

If dropped, has the potential to act as a torpedoNever leave a cylinder unattended!

Tank Pressure GaugeDisplay of the pressure of oxygen currently in the tank. Displays when the tank is opened

To open tank: use the key Only open once tank has

been connected to a yoke!Gauge reads zero when tank is empty AND when tank is closedGauge reads the current PSI even after closing tank

**Turn on O2 and check this gauge BEFORE every anesthetic procedure**

Tank Pressure Gauge (psi)

Refill line is at 500 psi (red zone)

Replace w/ new tank when the pressure is 100 psi

*Some clinics will require tanks to be changed much earlier.

Special VTI note: Run your tank until the ball drops

Gauge gives you the amount of O2 in psi but you set your flow rate in liters/minute…how can you tell how much time you have left until empty?

Calculating Oxygen Volume in Liters

Total volume of O2 left in your tank (liters) can be calculated by multiplying the pressure (psi) by:

__ for E tanks and __ for H tanks

Example:

Nitrous Oxide A full E cylinder contains 760 psi.Nitrous oxide is present in liquid AND gas forms inside the tank. When the tank is open, liquid evaporates into a gas as other gas leaves the tank.

The pressure of the tank doesn’t change (because of the constant replacement of the gas) until all liquid has been volatilized.

*The gauge will not drop until almost empty*Anesthetist should change the tank as soon as 500 psi is reached.

Pressure Reducing Valve aka Pressure Regulator

Regulates the pressure of the gas leaving the tank to flow through the linesReduces the pressure of oxygen that leaves the tank at 2200 psi to a safer psi. What is the safer psi?

Allows a constant flow of gas into the machine, despite pressure changes within the tank Can be measured with a line pressure gauge

In cases of E tanks and gas lines, the line pressure is preset at 50 psi, so there is usually no gauge seen

*Know what line we are measuring the pressure in*

Flow Meter Allows the flow rate of oxygen traveling through

the machine to be adjusted by the anesthetist. Reduces the psi AGAIN Oxygen does not reach the patient unless this is

turned on. Measured in liters per minute by a ball Ball rises in height, proportional to gas

*Read at center of ball

Calculating How Much Time is Left of O2

We already figured out the # of liters of oxygen in the tank:

Divide that amount by the flow rate you’re using:

330 L of O2 / 1 L/min = 330 minutes of use

Example: If you have a full tank and a higher flow rate of 2 L/min:

Oxygen Flush ValveButton that when depressed, rapidly delivers pure oxygen at a high flow rate

o Pure because:

o High rate because:

O2 goes directly from pressure reducing valve breathing system lungs

• Not to exceed 2 cm H2O on pressure manometer when in use

Oxygen Flush Valve

Seems dangerous…

When would we want to use this?

1. To dilute anesthetic in lines:

3. To fill reservoir bag (to give a breath)

*Note about that breath:

Watch the manometer!

PART 2: Anesthetic Vaporizer

Next stop as oxygen travels from the flow meter

Now that the gas is in the machine, it’s job is to mix with the liquid anesthetic and be delivered to the patient.

Begins with the vaporizer inlet port

VaporizerConverts the liquid anesthetic agent into a vapor.

Adds controlled amount of these vapors to the carrier gas “fresh gas”

The vaporizer must be on to deliver any inhalant anesthetics to the patient. Must press down on safety lock to turn dial

The flow meter must be on to supply the oxygen; otherwise nothing is delivered.

VaporizerAmount of anesthetic liquid left in vaporizer is visible in the indicator window. Refill by unscrewing cap of fill port

If for some reason the vaporizer is tipped over (usually the whole machine), turn the vaporizer off and run oxygen only through the machine for 15 minutes to flush it out.

Use the correct anesthetic with the correct vaporizer! (Iso vs. Sevo)

Vaporizer

The vaporizer has a inlet port and an outlet port

Optional: Common Gas Outlet aka Fresh Gas Outlet

Note: When switching between rebreathing and non-rebreathing systems, this is where you will connect your breathing tubes

*Our machines vary here*

Precision vs. Non PrecisionNon-precision vaporizers are simple, cheaper, and are typically used for anesthetics with low vapor pressure such as methoxyfluraneNon-precision vaporizers are located within the breathing circuit (VIC)

• Gas flows from the flow meter into the breathing tubes, which contain the vaporizer

*They are no longer commonly used;

we will focus on precision vaporizers

Non-precision Vaporizer

Precision Vaporizers

Precision vaporizers deliver a precise, controlled amount of anesthetic to the patient Expressed as a % which is chosen based on an

anesthetic’s MAC and the patient’s requirements

• Who chooses this?

Commonly used anesthetics can reach concentrations as high as 30% + if they are not controlled

Precision vaporizers are located outside of the

breathing circuit (VOC)

Factors Affecting Vaporizer Output Newer precision vaporizers compensate for the factors that

determine the concentration of anesthetic delivered.

(other than what you set it to)

Factors that are compensated for:

1. Temperature changes: Volatile anesthetics vaporize more rapidly at high temperatures

If not compensated for:

Precision Vaporizer Compensation

2. Carrier gas flow rates and respiratory rate effect amount of anesthetic delivered

If not flow-compensated:

3. Back pressure: Squeezing the reservoir bag while bagging your patient exerts pressure on the vaporizer outlet port

If not back pressure compensated: