190715_Anesthesia Machines Flashcards
Overview: Anesthesia machine
◦ Provides delivery of medical gases and vapors of volatile anesthetics in known concentrations to a common gas outlet
- These gases enter a breathing system
- Delivered to the patient during either spontaneous or mechanical ventilation
- Exhaled gases are removed from the breathing system
Standards of the anesthesia machine are overseen by:
◦ American National Standards Institute (ANSI)
- Prior to 2000 - older machines
◦ American Society for Testing and Materials (ASTM)
-Since 2000
◦ International Electrochemical Commission (IEC)
◦ Compressed Gas Association (CGA)
◦ Institute of Electrical and Electronics Engineers (IEEE)
◦ Federal Drug Administration (FDA)
Primary Components
Electrical supply
Battery backup
◦ 30 minutes
Alarms
◦ High, medium, low priority
Required monitors ◦ Inspired oxygen/CO2 ◦ Expired oxygen/CO2 ◦ Oxygen supply failure ◦ Hypoxic guard system ◦ Anesthetic vapor concentration ◦ Vital signs
Oxygen supply
◦ Pipeline supply
◦ Cylinder
Flowmeter
Oxygen flush valve
Vaporizers
◦ Calibrated
Waste gas system
Types of machines: see slides also for visual!
Datex Ohmeda ~ 3 at GT
Drager
Midray ~ Dr. L never seen
Specialty: Field, Mobile & MRI
Systematic way of thinking about it….
Nagelhout
◦ Supply, processing, delivery & Disposal
Barash
◦ Checkout of the anesthesia workstation (FDA checks)
Miller’s **
◦ High, intermediate & low-pressure system **
High Pressure System
The high-pressure system includes segments exposed to high pressure of auxiliary gas cylinders
◦ < 2000 psi
Components of the high-pressure system includes: ◦ 1. Auxiliary E – Cylinder ( tanks) ◦ 2. Yoke assembly ◦ 3. Burdon gauge ◦ 4. High pressure regulator
- Cylinders
Gases such as oxygen, nitrous oxide, air & carbon dioxide are supplied as cylinders
Vary in sizes A – H (Largest) ◦ Sizes A – E - Back up - ***Size E most common *** ◦ Sizes G – H - Banks - Back up for hospital supply ◦ Tank - Steel - Aluminum (longer!) -- For MRI environment
US Department of Transportation
Issues regulations ◦ Manufacture ◦ Marking/labeling ◦ Filling ◦ Handling ◦ Transport ◦ Storage ◦ Disposal of cylinders
Also have standards
◦ Compressed gas association
◦ National Fire Protection Association
◦ United States Pharmacopeia/National Formulary (USP/NF) - Sets purity of medical gases
CO2 color (US)
Grey
Medical AIr (US)
Yellow
Gas
625L full take
1800psi
1,5
N (US)
Black
N2O (US)
Blue
Liquid & Gas
1590L full take
750psi
3,5
O2 (US)
Green
Gas
660L full take
2200psi
2,5
Vacuum suction (US)
White
WAGD (Evac)
Purple
Yoke Assembly
Orient tanks Gas tight seal Unidirectional flow of gases Contains a filter Some have check valve ◦ Stops leaking into atmosphere ◦ Stops transfer between tanks *** ***Pin index safety system (PISS)***
Nitrous Cylinder
Have to weight the cylinder to figure out amount of gas left
Pressure remains constant until all the liquid has turned to gas
◦ Pressure does not start to drop until about 75% of the tank is used
◦ About 250 - 400 ml’s remain
Cylinder safety systems
1. Frangible disk ◦ Burst under extreme pressure 2. Fusible plug ◦ Melts at a predetermined temperature ◦ Made of bismuth, lead, tin & cadmium ◦ BLT with cheese
High Pressure Regulator
Reduces the high and variable pressure delivered from a cylinder to a lower and more constant pressure suitable for the anesthesia machine
Pressure regulators are preset at the factory
◦ Typically between 40 -45 psig
were as the hospital supply is 50-55 psi, system auto pulls from highest pressure source
This ensures the pipeline gas is used preferentially to the cylinder
Intermediate Pressure System
Receives gases from the pressure regulator or pipeline inlet
Components include: 1. Hospital supply (pipeline inlet) 2. Oxygen flush valve 3. Pneumatic safety systems/electrical system (on switch) ◦ Oxygen supply failure alarms ◦ Oxygen failure protection devices 4. Auxiliary oxygen flowmeter 5. Second stage regulator
- Hospital Supply
Oxygen
◦ Typically stored as a liquid
◦ -184 degrees Celsius
◦ Supplied to the hospital as a gas @ 50 psi
◦ Working pressure of the anesthesia machine
◦ Multiple shut off valves between supply and anesthesia machine
Nitrous
◦ Typically stored in H cylinders
- Hospital Supply Connections
Diameter index safety system (DISS)
◦ Ensures only the correct anesthesia gas can be connected
◦ Sized and threaded differently
- Body, nipple, and nut combintion
Contains: ◦ Filter - Stop contaminants ◦ Check valve - Ensures unidirectional flow ◦ Pressure gauge - Pipeline pressure
Quick connections – older Gas specific Typically to wall outlets Are manufacture specific ◦ Problem…. ◦ Ohmeda will not connect to Chemeron
- Oxygen Flush Valve
Provides 100% oxygen to the anesthesia circuit
Enters the circuit downstream from the vaporizers – directly to common gas outlet
Flow rate between 35 – 75 L/minute
Protected by rim (or recessed) to lessen the chance of accidental activation Hazards
◦ **Barotrauma
- Stuck valve
- If used during inspiratory phase of mechanical ventilation
– Older - Ventilator relief valve closed & APL out of circuit
– Newer - Fresh gas decoupling valve
◦ **Awareness
- Dilute anesthetic gases
- res bag
- checks
- bellows
Fresh gas decoupling
limit barotrauma
- Electrical system
Electrical power is supplied to the gas machine through a single power cord Possibility of loss of power
◦ Emergency generator and batter back-up
Must have a battery backup that lasts at least 30 minutes of limited operation! FDA
◦ Each machine is different
◦ Typically, patient monitors are discontinued
Do not plug anything into into the machine receptacles
◦ May trip circuit breakers on back of machine
- Pneumatic Safety Systems
Engineered to help prevent the delivery of a hypoxic gas mixture to the patient
Oxygen influences the flow of all other gases
In older anesthesia machines, the flows of oxygen and nitrous oxide were independent and were not pneumatically or mechanically interfaced
Therefore, abrupt or insidious oxygen pressure failure had the potential to deliver a hypoxic mixture to the patient
“The anesthesia gas supply device shall be designed so that whenever oxygen supply pressure is reduced below the manufacturers specified minimum, the delivered oxygen concentration shall not decrease below 19% at the common gas outlet.”*
Oxygen supply failure alarm
Older Ohmeda Machines
◦ Audible indications when pneumatic system is turned on (oxygen filling whistle)
◦ When oxygen pressure drops below 38 psig the oxygen failure whistle valves opens
◦ Whistle sounds until oxygen pressure drops below 6 psig
◦ **At 30 psig, the supply of anesthesia gases are stopped **Except O2
Fail-safe devices
Fail save valves are designed to prevent the delivery of hypoxic gas mixtures from the machine in the event of failure of oxygen supply
◦ PRESSURE not flow!
Protects against unrecognized exhaustion of oxygen delivery from either the pipeline or attached oxygen tank
Fail safe devices either
◦ proportionally decreases the flow of all gases
or
◦ shuts off (threshold) flow of all other gases except oxygen
based on manufacture set pressures
Limits:
◦ Does not prevent anesthesia gases from flowing
***if cross connected?
◦ Works even if the wrong gas is supplied (pneumatic devices – stupid)
Fail safe device: Drager
proportionally decreases the flow of all gases
Fail safe device: Datex Ohmeda
shuts off (threshold) flow of all other gases except oxygen (O2 supply presser < 20psig)
- Auxiliary Oxygen Flowmeter
Not a mandatory requirement, but on almost all anesthesia machines
Allows for the use of low flow oxygen without using the anesthesia circuit
◦ Typically used for monitored anesthesia care
Most often accessible when the pneumatic power switch is off
◦ Can be used in an emergency, even without machine power
◦ However uses same pipeline supply or attached E – cylinder (Even if contaminated…)
May serve as potential source of oxygen for jet ventilation
- Second Stage Pressure Regulator
Located downstream from the gas supply sources in the intermediate pressure system
Supply constant pressure to the flow control valves and the proportioning system
◦ Protects against fluctuations of pipeline pressure
Lowers the pressure to 14 - 35 psi ◦ Depends on the workstation ◦ Typically: ◦ ***Oxygen: 14 psi***ALWAYS LAST GAS FLOWING ◦ ***Nitrous oxide: 26 psi***
Ensures that oxygen is the last gas flowing
Low Pressure System
Located between the flow control devices and common gas outlet
Pressure in this section is slightly above atmospheric
Pressure in this section is variable
Contains:
◦ 1. Flowmeters / vaporizer
◦ 2. Hypoxia prevention safety devices
◦ 3. Unidirectional valves (info only)
◦ 4. Pressure relief devices (info only)
◦ 5. Anesthesia vaporizers/vaporizer manifold (info only) ◦ 6. Common gas outlet
- Flowmeters
Contains
◦ Flow control valves
◦ Flow tubes
Regulates the flow of gases entering the breathing circuit
Traditional are mechanically controlled
Newer are an electronic interface
The oxygen and nitrous flow valves are linked mechanically or pneumatically to prevent a hypoxic mixture
Selected flows are directed into the vaporizer
- Flowmeter
Consists of: ◦ Flow control knob ◦ A tapered needle valve ◦ Valve seat ◦ Valve stops ◦ Float ◦ Float stops
- Flow tubes (Variable orifice or Thorpe tubes)
Narrow at bottom & widen vertically
Annular space: between float & tube
◦ Laminar – low flow – viscosity of gas
◦ Turbulent – high flow – density of gas
Calibrated for SPECIFIC GAS
Indicator float – hovers at equilibrium
Placed in series
- Flow tubes (electronic flow sensors)
Newer machines use electronic flow sensors
Multiple different methods to measure
Depend on electrical power to provide display
Must have a backup to control & display O2 flows
Chamber of know volume:
amount of heat required to maintain the set temperature is proportional to specific heat and gas flow rates
- Flow tubes (O2 fail safe)
O2 source (tube) closest to outlet
- Hypoxia prevention devices
A proportioning system is to prevent the creation and delivery of hypoxic mixtures
Designed to prevent an operator selected delivery of oxygen concentration below 21%
The machine automatically limits the amount of nitrous oxide so a hypoxic mixture cannot be delivered
Accomplished with a pneumatic-mechanical interface between the oxygen and nitrous oxide flows
Specific devices vary among anesthesia machine manufactures
Sensitive oxygen ratio controller system (Drager)
Pneumatic – mechanical interlock
Opening the oxygen flow creates a backpressure in the chamber opening the nitrous oxide flow
Maintains a ratio of 25% oxygen to 75% nitrous oxide flow into breathing circuit
***75:25 ~ N2O:O2
Needs at least 200 mL/min to operate
Link – 25 Proportion Limiting (Datex-Ohmeda)
Mechanical integration of nitrous oxide and oxygen flow control valves
Can adjust either valve – but always maintains a flow ratio of 3:1
Balanced secondary regulator
◦ Oxygen @ 30 psig
◦ Nitrous pressure based on oxygen pressure
Maintains oxygen concentration of at least 25%
- **N2O = 15 teeth
- **O2 = 29 teeth
- Common gas outlet
Receives all the gases and vapors from the machine and delivers the mixture to the breathing circuit
Is a 15 mm female slip joint fitting
Should not be used to administer supplemental oxygen to a patient
5 pathways of oxygen
- Flow to the fresh gas flowmeter
- Powers the oxygen flush valve
- Activates the fail-safe valve/mechanism
- Activates the oxygen supply low pressure alarm
- Compresses the bellows of the ventilator
Anesthesia Machine Check (Two checks )
- Complete a thorough daily check (machine check)
2. Circuit check before each new surgical case
Machine Check
- Emergency equipment
- High pressure system check
- Low pressure system check
- Oxygen sensor
- Scavenging system
- Ventilator
- Breathing system
- Monitors
- Final check
Machine check
1. Emergency equipment
◦ 1. Ambu bag
◦ 2. Back up oxygen cylinder (>1000 psig)
◦ 3. Functioning suction with yankauer
Machine Check
2. High pressure system
1. Check O2 cylinder supply ◦ Open cylinder and check PSI (>1000) ◦ Close cylinder ◦ Depress O2 flush 2. Disconnect pipeline supply from the wall
Machine Check
3. Low pressure system check
1. Check vaporizers ◦ Mounted, filled, and interlock works 2. Check low pressure system ◦ Suction bulb to common gas outlet ◦ Squeeze bulb until fully collapsed ◦ Verify bulb stays deflated for 10 seconds 3. Turn on master switch ◦ Listen for oxygen disconnect alarm (whistle) ◦ Reconnect pipeline pressure ◦ Ensure pipeline pressure is > 50 psig 4. Test flowmeters ◦ Adjust flow of all gases through their range ◦ Attempt to create a hypoxic mixture
Machine Check
4. Oxygen sensor & Breathing circuit
- Calibrate O2 sensor
◦ Ensure reads 21% in room air
◦ Verify low O2 alarm (set to 30%) ~ 30-21% = buffer
◦ Re-install sensor and flush with O2 - now reads > 90% - Install breathing circuit
Machine Check
5. Scavenging System
- Ensure proper connection of scavenging system
- Adjust waste gas vacuum
- Fully open APL valve
- Occlude Y piece, ensure gauge reads < 10 cm H2O
- With Y piece occluded, depress O2 flush ensure the reservoir bag distends, and the pressure gauge reads < 10 cm H2O
Machine Check
6. Ventilation system
- Place a second breathing bag on Y piece
- Set appropriate ventilator setting for next patient
- Set O2 @ 5 L
- Turn ventilator on and fill bellow with flush valve
- Verify bellows deliver adequate tidal volumes
- Check function of unidirectional valve
- Squeeze bag and check over pressure alarm
- Set to manual ventilator mode
- Ensure ability to manual ventilate
- Turn of ventilator and remove breathing bag
Machine Check
7. Check breathing system (Positive pressure check)
Leak Check = EACH PT!!!
- Set all gas flow to zero
- Close APL valve an occlude the Y piece
- Pressurize the breathing system to 30 cm H2O
- Ensure pressure remains fixed for at least 10 seconds 5. Fully open APL valve and allow bag to self deflate and flows through the scavenger
Machine Check
8. Monitors
- Set anesthesia monitors for next patient
Machine Check
9. Final Check
- Vaporizers off
- APL valve open
- Selector switch set to bag
- All flowmeters set to zero
- Suction available
- Monitors set appropriately
- Circuit on, CO2 sampling line connected, & correct mask on
