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NURA 641 Intro to Nurse Anesthesia > 190715_Anesthesia Machines > Flashcards

190715_Anesthesia Machines Flashcards

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1
Q

Overview: Anesthesia machine

A

◦ 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
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2
Q

Standards of the anesthesia machine are overseen by:

A

◦ 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)

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3
Q

Primary Components

A

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

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4
Q

Types of machines: see slides also for visual!

A

Datex Ohmeda ~ 3 at GT

Drager

Midray ~ Dr. L never seen

Specialty: Field, Mobile & MRI

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5
Q

Systematic way of thinking about it….

A

Nagelhout
◦ Supply, processing, delivery & Disposal
Barash
◦ Checkout of the anesthesia workstation (FDA checks)
Miller’s **
◦ High, intermediate & low-pressure system **

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6
Q

High Pressure System

A

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
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7
Q
  1. Cylinders
A

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
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8
Q

US Department of Transportation

A 
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

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9
Q

CO2 color (US)

A

Grey

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10
Q

Medical AIr (US)

A

Yellow

Gas

625L full take

1800psi

1,5

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11
Q

N (US)

A

Black

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12
Q

N2O (US)

A

Blue

Liquid & Gas

1590L full take

750psi

3,5

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13
Q

O2 (US)

A

Green

Gas

660L full take

2200psi

2,5

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14
Q

Vacuum suction (US)

A

White

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15
Q

WAGD (Evac)

A

Purple

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16
Q

Yoke Assembly

A 
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)***
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17
Q

Nitrous Cylinder

A

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

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18
Q

Cylinder safety systems

A 
1.  Frangible disk 
◦ Burst under extreme pressure
2.  Fusible plug 
◦ Melts at a predetermined temperature 
◦ Made of bismuth, lead, tin &amp; cadmium 
◦ BLT with cheese
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19
Q

High Pressure Regulator

A

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

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20
Q

Intermediate Pressure System

A

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
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21
Q
  1. Hospital Supply
A

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

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22
Q
  1. Hospital Supply Connections
A

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
23
Q
  1. Oxygen Flush Valve
A

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
24
Q

Fresh gas decoupling

A

limit barotrauma

25
Q
  1. Electrical system
A

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

26
Q
  1. Pneumatic Safety Systems
A

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.”*

27
Q

Oxygen supply failure alarm

A

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

28
Q

Fail-safe devices

A

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)

29
Q

Fail safe device: Drager

A

proportionally decreases the flow of all gases

30
Q

Fail safe device: Datex Ohmeda

A

shuts off (threshold) flow of all other gases except oxygen (O2 supply presser < 20psig)

31
Q
  1. Auxiliary Oxygen Flowmeter
A

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

32
Q
  1. Second Stage Pressure Regulator
A

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

33
Q

Low Pressure System

A

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

34
Q
  1. Flowmeters
A

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

35
Q
  1. Flowmeter
A 
Consists of: 
◦ Flow control knob 
◦ A tapered needle valve 
◦ Valve seat 
◦ Valve stops 
◦ Float 
◦ Float stops
36
Q
  1. Flow tubes (Variable orifice or Thorpe tubes)
A

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

37
Q
  1. Flow tubes (electronic flow sensors)
A

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

38
Q
  1. Flow tubes (O2 fail safe)
A

O2 source (tube) closest to outlet

39
Q
  1. Hypoxia prevention devices
A

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

40
Q

Sensitive oxygen ratio controller system (Drager)

A

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

41
Q

Link – 25 Proportion Limiting (Datex-Ohmeda)

A

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
42
Q
  1. Common gas outlet
A

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

43
Q

5 pathways of oxygen

A
  1. Flow to the fresh gas flowmeter
  2. Powers the oxygen flush valve
  3. Activates the fail-safe valve/mechanism
  4. Activates the oxygen supply low pressure alarm
  5. Compresses the bellows of the ventilator
44
Q

Anesthesia Machine Check (Two checks )

A
  1. Complete a thorough daily check (machine check)

2. Circuit check before each new surgical case

45
Q

Machine Check

A
  1. Emergency equipment
  2. High pressure system check
  3. Low pressure system check
  4. Oxygen sensor
  5. Scavenging system
  6. Ventilator
  7. Breathing system
  8. Monitors
  9. Final check
46
Q

Machine check

1. Emergency equipment

A

◦ 1. Ambu bag
◦ 2. Back up oxygen cylinder (>1000 psig)
◦ 3. Functioning suction with yankauer

47
Q

Machine Check

2. High pressure system

A 
1.  Check O2 cylinder supply 
◦ Open cylinder and check PSI (>1000) 
◦ Close cylinder 
◦ Depress O2 flush 
2.  Disconnect pipeline supply from the wall
48
Q

Machine Check

3. Low pressure system check

A 
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
49
Q

Machine Check

4. Oxygen sensor & Breathing circuit

A
  1. 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%
  2. Install breathing circuit
50
Q

Machine Check

5. Scavenging System

A
  1. Ensure proper connection of scavenging system
  2. Adjust waste gas vacuum
  3. Fully open APL valve
  4. Occlude Y piece, ensure gauge reads < 10 cm H2O
  5. With Y piece occluded, depress O2 flush ensure the reservoir bag distends, and the pressure gauge reads < 10 cm H2O
51
Q

Machine Check

6. Ventilation system

A
  1. Place a second breathing bag on Y piece
  2. Set appropriate ventilator setting for next patient
  3. Set O2 @ 5 L
  4. Turn ventilator on and fill bellow with flush valve
  5. Verify bellows deliver adequate tidal volumes
  6. Check function of unidirectional valve
  7. Squeeze bag and check over pressure alarm
  8. Set to manual ventilator mode
  9. Ensure ability to manual ventilate
  10. Turn of ventilator and remove breathing bag
52
Q

Machine Check

7. Check breathing system (Positive pressure check)

A

Leak Check = EACH PT!!!

  1. Set all gas flow to zero
  2. Close APL valve an occlude the Y piece
  3. Pressurize the breathing system to 30 cm H2O
  4. 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
53
Q

Machine Check

8. Monitors

A
  1. Set anesthesia monitors for next patient
54
Q

Machine Check

9. Final Check

A
  1. Vaporizers off
  2. APL valve open
  3. Selector switch set to bag
  4. All flowmeters set to zero
  5. Suction available
  6. Monitors set appropriately
  7. Circuit on, CO2 sampling line connected, & correct mask on

NURA 641 Intro to Nurse Anesthesia (8 decks)

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