Parts of the Anesthetic Machine A&A Pages

Purpose of the Anesthetic Machine A 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 circuit  Gases exhaled from the patient are scavenged OR can be re-circulated (once CO 2 has been removed) *Can also be used to deliver just oxygen during recovery or in an emergency* 2

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, CO 2 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 Cylinders  Most 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 Cylinders  Tanks 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- Safety  In 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- Safety  Combustible gases- avoid flames and sparks!  Tanks must be stored in a secure location  If dropped, has the potential to act as a torpedo  Never leave a cylinder unattended!

Tank Pressure Gauge  Display 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 closed  Gauge reads the current PSI even after closing tank **Turn on O 2 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 O 2 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 O 2 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 lines  Reduces 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 O 2 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 O 2 / 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 Valve  Button that when depressed, rapidly delivers pure oxygen at a high flow rate o Pure because: o High rate because: O 2 goes directly from pressure reducing valve  breathing system  lungs Not to exceed 2 cm H 2 O 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

Vaporizer  Converts 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.

Vaporizer  Amount 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 Precision  Non-precision vaporizers are simple, cheaper, and are typically used for anesthetics with low vapor pressure such as methoxyflurane  Non-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: