Anesthesia Machine Flashcards
Function of the 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 is are governed by?
American National Standards Institute (ANSI) Prior to 2000
American Society for Testing and Materials (ASTM) since 2000
Contemporary Components of the machine are?
Electrical supply Battery back- 30 minutes Alarms- High, medium, low priority Required monitors -inspired O2 -expired CO2 -Oxygen Supply failure -Hypoxic guard system -Anesthetic vapor concentration -Vital signs Oxygen supply Flowmeter O2 Flush valve Vaporizers -Calibrated Waste gas system
Systematically how does Nagelhout categorized the machine
Nagelhout
Supply, processing, delivery, Disposal
Systematically how does Barash categorized the machine
Barash
Checkout of the anesthesia workstation
Systematically how does Miller categorized the machine
Miller’s
High, intermediate, low-pressure system
The High Pressure system includes segments exposed to high pressure of auxiliary gas cylinders of how much pressure?
< 2000 psi
Components of the high-pressure system are?:
- Auxiliary E – Cylinder
- Yoke assembly
- Burdon gauge
- High pressure regulator
Describe Cylinder sizes A-E
Sizes A – E
Back up
Size E most common
Describe cylinder sizes G-H
Sizes G – H
Banks
Back up for hospital supply
How are cylinders sized and material they are made of:
Vary in sizes A-H
Steel
Aluminum- For MRI environment
DOT issues regulations for O2 tanks, who sets purity of medical gases?
United Stated Pharmacopeia/ National Formulary (USP/ NF)
Carbon Dioxide Color code
US Grey
ISO Grey
Medical Air Color code
US Yellow
ISO Black and White
Nitrogen Color code
US Black
ISO Black
Nitrous Oxide Color code
US Blue
ISO Blue
Oxygen Color code
US green
ISO white
Vacuum (Suction) Color code
US white
ISO Yellow
WAGD (EVAC) Color code
US Purple
ISO Purple
Describe the Yoke Assembly
- Orient tanks
- Gas tight seal
- Unidirectional flow for gases
- Contains a filter
5Check valve
- stops leaking into atmostphere
-Stops transfer between tanks
Pin Index Safety System (PISS) for
Air, O2, Nitrous Oxide
Air-1,5
O2- 2,5
N2O-3,5
E- cylinder capacity
660 L
1900 PSI
H cylinder Capacity
6900 L
2200 PSI
Properties of O2 physical state (room temp) and full tank pressure
Gas at room temp 2200 psi full tank capacity
Properties of Nitrous Oxide physical state (room temp) and full tank pressure
Liquid and gas at room temp
750 psi full tank
Describe the Nitrous Cylinder
750 PSI
1590 Liters of Gas
Liquified gas…
Have to weigh 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
What are the safety systems a cylinder
- Frangible disk
Burst under extreme pressure - Fusible plug
Melts at a predetermined temperature
Made of bismuth, lead, tin & cadmium
BLT with cheese
What is the function of the 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.
High Pressure regulators are preset at the factory at? and what does that ensure?
Typically between 40 -45 psig
This ensures the pipeline gas is used preferentially to the cylinder
Hospital Oxygen supply
Typically stored as a liquid -184 degrees Celsius.
Supplied to the hospital as a gas @50 psi.
50 psi is the working pressure of the anesthesia machine
Multiple shut off valves between supply and anesthesia machine
How is nitrous stored?
Typically in stored in H cylinders
Hospital Supply Connections uses what safety system
Diameter Index Safety System (DISS).
Explain the Diameter Index Safety System (DISS).
Ensures only the correct anesthesia gas can be connected
What does the Diameter index safety system (DISS) contains/ components?
Contains: Filter-Stop contaminants Check valve Ensures unidirectional flow Pressure gauge Pipeline pressure Sized and threaded differently Body, nipple, and nut combination
Describe the Hospital Supply Connections
Quick connections – older Gas specific Typically to wall outlets Are manufacture specific -Problem…. -Ohmeda will not connect to Chemeron
Oxygen Flush Valve provides?
And where is it attached?
100% oxygen to the anesthesia circuit at 35-75 L/minute.
Enters the circuit downstream from the vaporizers – directly to common gas outlet.
How is the 2 Oxygen Flush Valve protected
Protected by rim to lessen the chance of accidental activation
What are the hazards of the O2 flush valve
*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
Describe the electrical system of the anesthesia machine and how the anesthesia machine is powered?
Electrical power is supplied to the gas machine through a single power cord.
Must have a battery backup that lasts at least 30 minutes of limited operation!
Each machine is different
Typically, patient monitors are discontinued
Explain the 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
How did manufacturers incorporate the pneumatic safety systems?
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.”
Explain oxygen supply failure alarms on 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.
What Fail-safe devices and explain how they work?
- Fail safe 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
Works even if the wrong gas is supplied (pneumatic devices – stupid)
What are the 2 limitation of fail safe devices?
Does not prevent anesthesia gases from flowing
Works even if the wrong gas is supplied (pneumatic devices – stupid)
Explain the Fail safe device: Oxygen failure protection device in Drager
O2 supply is at 50 psig pushes the piston which inturns pushes the spring load nozzle open and which allows N2O . As O2 supply decreases the spring loaded nozzle closes of N2O
Explain the Fail safe device in: Datex Ohmeda
Oxygen supply is greater than 20 psig pushes the diaphragm of the open which allows N2O to flow. As the O2 supply gets bellow 20 psig the diaphragm closes and the flow of N2O is stopped.
What is 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
Functions of the Second Stage Pressure Regulator
- Ensures that oxygen is the last gas flowing.
- Supply constant pressure to the flow control valves and the link proportioning system
- Protects against fluctuations of pipeline pressure
*Located downstream from the gas supply sources in the intermediate pressure system
Lowers the pressure to 14 - 35 psi
Depends on the workstation
Typically:
Oxygen: 14 psi
Nitrous oxide: 26 psi
Where is the Low Pressure System located
Located between the flow control devices and common gas outlet
Pressure in this section is slightly above atmospheric
What are the components of the low pressure system?
H U F P A C
- Hypoxia prevention safety devices
- Unidirectional valves (info only)
- Flowmeters
- Pressure relief devices (info only)
- Anesthesia vaporizers/vaporizer manifold (info only)
- Common gas outlet
Describe the purpose of the flowmeters
Regulates the flow of gases entering the breathing circuit
Flow meter contains
- Flow control valves
2. Flow tubes
How are the flow valves and in the flowmeters linked?
The oxygen and nitrous flow valves are linked mechanically or pneumatically to prevent a hypoxic mixture
Flowmeters control the flow of gases Traditional vs. electronic
Traditional are mechanically controlled
Newer are an electronic interface
Flowmeter consists of
Consists of: Flow control knob A tapered needle valve Valve seat Valve stops Float Float stops
What are the types of flow tubes? Describe them.
Variable orifice or Thorpe tubes
Narrow at bottom and widens vertically
Annular space: between float and tube
Calibrated for SPECIFIC GAS
Indicator float – hovers at equilibrium
Placed in series
What is Laminar flow vs. Turbulent flow
Laminar – low flow – viscosity of gas
Turbulent – high flow – density of gas
Flow tubes chamber of know volume
Chamber of know volume – the amount of heat required to maintain the set temperature is proportional to specific heat and gas flow rates.
Flow tubes on newer machines
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
What are 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
Needs at least 200 mL/min to operate
Common gas outlet receives all gages and vapors from?
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
How and when should Anesthesia Machine Checks be completed?
Two checks
- Complete and thorough daily check
- Circuit check is performed before each new surgical case
The Intermediate Pressure System receives gases from?
from the pressure regulator or pipeline inlet
Components of the Intermediate Pressure System are:
- Hospital supply (pipeline inlet)
- Oxygen flush valve
- Pneumatic safety systems/electrical system (on switch)
Oxygen supply failure alarms
Oxygen failure protection devices - Auxiliary oxygen flowmeter
- Second stage regulator
Where is the second stage regular located?
*Located downstream from the gas supply sources in the intermediate pressure system
What are 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
