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Scientific Principles > Week 5 - Anesthesia Machine Overview > Flashcards

Week 5 - Anesthesia Machine Overview Flashcards

1
Q

What does the anesthesia machine do?

A
  • Deliver gases to keep patient alive and asleep
  • Makes sure those gases don’t contaminate the air
  • Means to provide mechanical ventilation
  • Means to monitor the patient and anesthetic gases
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2
Q

What is the machine outlet (common gas outlet)?

A

where all gases get delivered to the circuit

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3
Q

How do gases come to the anesthesia gas machine?

A

Supply: at the back of the machine via:

  • Pipeline (DISS): wall outlets, connecting valves and hoses, filters/check valves, pressure gauges
  • Cylinders (PISS): hanger yokes, filters/check valves, pressure gauge, pressure regulators
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4
Q

How does the anesthesia gas machine prepare gases before their delivery to the patient?

A

Processing: Happens within the machine, proximal to common gas outlet

Fail-safe, Flowmeters, O2 flush, Low O2 pressure alarms, Ventilator driving gas, Proportioning systems (hypoxic guard), O2 second-stage regulator, Vaporizers, Check valves distal to vaporizers, Common gas outlet

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5
Q

How is the interaction of gases with the patient controlled and monitored with the anesthesia machine?

A

Delivery: occurs at common gas outlet to breathing circuit

  • Common gas outlet: gas delivery hose connecting and breathing circuit
  • Circle system circuit: nonrebreathing flow (inspiratory and expiratory valves) and CO2 absorption
  • Ventilators (piston or bellows type)
  • Integral Monitors: O2 analysis, disconnect alarm, spirometry, capnography, airway pressure, ventilator alarms
  • Addition of positive end-expiratory pressure
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6
Q

How are gases disposed of in the anesthesia machine?

A

Via the scavenger system

  • closed (active/passive)
  • open
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7
Q

What are the two main components of the anesthesia machine?

A

Electrical System

Pneumatic System

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8
Q

What are the components of the electrical system in an anesthesia machine?

A
  • Master switch (turns on electrical and pneumatic system inside machine, does NOT need to be on for cylinder pressure to be on)
  • Power failure indicator (visible and audible)
  • Reserve power (battery back up)
  • Electrical outlets (convenience)
  • Data ports
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9
Q

What are the components of the pneumatic system in an anesthesia machine?

A

High Pressure System

Intermediate Pressure System

Low Pressure System

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10
Q

What are the electrical sources of an anesthesia machine?

A

Single power cord

Battery backup for 30 minutes

Convenience outlets (intended for monitors, may not supply electricity if machine is on battery back up) – don’t use for heat devices like Bair huggers (draw a lot of amperage)

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11
Q

What devices on an anesthesia machine are NOT reliant on electrical power?

A
  • Spontaneous/manual assist ventilation
  • Mechanical flowmeters
  • Scavenging system
  • Variable bypass vaporizers
  • Auxiliary flowmeters
  • Monitoring with you 5 senses!
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12
Q

What devices on an anesthesia machine require wall outlet electrical power?

A
  • Mechanical ventilators
  • Electronic monitors
  • Digital flowmeter displays for electronic flowmeters
  • Vaporizers with electronic controls or injection control (Desflurane, Aladin cassettes)
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13
Q

What are the pressures in the High, Intermediate, and Low pressure systems of an anesthesia machine?

A

High Pressure System = 1900-2200 psi

Intermediate Pressure System = 37-55 psi

Low Pressure System = variable < 37 psi

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14
Q

What are the components of the High Pressure System of an anesthesia machine?

A
  • Hanger Yoke (PISS)
  • Gas Cylinders (E)
  • Cylinder Pressure Gauge (Electronic or Bourdin type)
  • Cylinder Pressure Regulators
  • Check Valve
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15
Q

What are the cylinder gas sources for an anesthesia machine and their color, service pressure, capacity, and pin position?

A

Oxygen: green (US), 1900-2200 psi, 660L, PISS 2-5

Nitrous Oxide: blue, 745 psi, 1600 L, PISS 3-5

Air: yellow (US), 1800-1900 psi, 600 psi, PISS 1-5

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16
Q

What is the function of pressure regulators?

A

Reduce high and variable pressures delivered from the cylinder to more constant usable pressures

  • Maintains a regular flow rate even as pressure may decrease from the cylinder
  • Each gas has a separate pressure regulator

*Pressure from cylinders are down regulated to <50 psi so the machine will get its supply from the wall pressure instead of from the higher pressure tank

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17
Q

What are second stage pressure regulators?

A

Some machines use two regulators whereby the second regulator delivers the gas at slightly above atmospheric pressure to the downstream components (i.e. flowmeters) — reduce pressure from pipeline to flowmeters

Helps in providing a smooth constant flow of gas irrespective of fluctuations in pipeline pressures due to peak/trough demands in the system

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18
Q

What is the purpose of cylinder pressure relief valves?

A

Vent the contents of the cylinder into the atmosphere should dangerous pressures develop inside the cylinder

  • Required by the American Society for Testing and Materials (ASTM) standards
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19
Q

What are check valves?

A

One way flow valves or unidirectional flow valves

Prevent back flow of gas or permit directional gas flow

  • Inspiratory and expiratory valves on circuit
  • Between cylinders so they don’t flow into each other or exit of gas from machine when no cylinder present
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20
Q

What are the components of the Intermediate Pressure System of an anesthesia machine?

A
  • Master switch (when OFF, pressure in intermediate system falls to 0)
  • Pipeline inlet connections (DISS) (check valve at inlet to prevent reverse gas flow from machine to pipeline)
  • Pipeline pressure gauges (should read 50-55 psi)
  • Oxygen pressure failure device (Fail Safe)
  • Oxygen supply failure alarm
  • Gas selector switch
  • Second stage pressure regulator
  • Oxygen Flush
  • Flow adjustment controls
  • Alternate oxygen flow in case of electrical failure (Aysis)
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21
Q

What does the alternate O2 delivery system in an anesthesia machine require?

A

Either pipeline supply or a reserve oxygen cylinder to be connected

The System Switch to be in the ON position

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22
Q

What steps do you take if there is a loss of pipeline (wall) gas?

A

1) Don’t attempt to fix the oxygen analyzer (trust it until proved wrong) – if O2 analyzer doesn’t warn of the crossover, the pulse ox will
2) Turn on backup O2 cylinder/Disconnect pipeline – check FiO2 monitor, if it doesn’t rise ventilate pt w/ Ambu bag with room air
3) Use low flow O2, maintain anesthesia w/ volatile agent
4) Turn off ventilator and ventilate manually through circle system
5) Call for help if needed, calculate time remaining for current cylinder
6) Find out how long the problem is expected to last
7) Don’t reconnect pt to pipeline until gas supply is tested

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23
Q

What are the components of the Low Pressure System of an anesthesia machine? (7)

A
  • Flowmeters
  • Hypoxic guard systems (O2 - N2O link system)
  • Unidirectional check valve (Aespire)
  • Pressure relief device
  • Common gas outlet (may be internal on newer machines)
  • Auxiliary oxygen flowmeter
  • Breathing circuit
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24
Q

What are the types of flowmeters?

A

Electronic

Variable Orifice (Thorpe):

  • Low flows = laminar: viscosity, Hagen-Poiseuille law
  • High flows = turbulent: density, Graham’s law
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25
Q

What is the flow in variable orifice flowmeters dependent on?

A

Pressure change across constriction

Magnitude of annular opening

Physical properties of gas (changes in temp/pressure, density governs flow in places of turbulance)

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26
Q

Which float types do you read at the top and which do you read at the middle?

A

Read at top:

  • Non-rotating
  • Plumb-bob
  • Skirted
  • “H”

Read at middle:
-Ball

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27
Q

Where do you want the oxygen located in the flowmeter sequence?

A

Closest to the patient

  • If a flowmeter closer to the pt had a leak then the oxygen could leak from that flowmeter and not be delivered to the pt
  • Still need to check gas analysis since you can still have an issue regardless of placement
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28
Q

What are the advantages and disadvantages of Circle Breathing Circuits?

A

Advantages:

  • Stable inspired concentration
  • Conserve moisture and heat
  • Prevention of OR pollution
  • Low gas flows

Disadvantage: Complex design

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29
Q

Where are unidirectional check valves located in an anesthesia machine (Aespire) and what are their function?

A

Located between the vaporizers and the common gas outlet upstream of where the oxygen flush flow joins the fresh gas flow

Prevents backpressure to the vaporizers and flowmeters from positive pressure in the breathing circuit
Negative pressure leak test checks function of the valve

30
Q

What would you expect to see if an expiratory or inspiratory valve “sticks” or malfunctions?

A

Expiratory malfunction: rebreathing CO2, increase pressures

Inspiratory malfunction: increase in peak pressure due to trying to ventilate against a valve

31
Q

What is the requirement of the American Society for Testing and Materials (ASTM) standard for reservoir bags?

A

Less than 1.5 L = pressure should not be less than 30 or more than 50 cm H2O when expanded 4x

More than 1.5 L = pressure should not be less than 35 or greater than 60 cm H2O when expanded 4x

Appropriate size for pt = 2-5x pt’s tidal volume

32
Q

What is the purpose of the reservoir bag on an anesthesia machine?

A
  • Reservoir
  • A/C (manual) ventilation
  • Visual/Tactile monitor
  • Protects from excess pressure
33
Q

What is a caution of the ADU machine related to O2?

A

There is a calculated O2 concentration on the screen but you want to make sure to look at the actual FiO2 concentration

34
Q

What are major causes of pollution from anesthesia machines?

A

Anesthetic Technique:

  • Failure to turn off agent at end of case
  • Mask fit
  • Flushing circuit
  • Filling vaporizers
  • Uncuffed ET tubes

Equipment Issues:

  • Leaks
  • Poorly functioning scavenger
35
Q

What are the NIOSH trace gas recommendations?

A

Either Agent Alone:

  • Halogenated agent alone = 2 ppm
  • N2O = 25 ppm

Combined Halogenated agent/N2O:

  • Halogenated agent = 0.5 ppm
  • N2O = 25

Dental Facilities (N2O alone) = 50

36
Q

What are the types of scavenging systems?

A

Active: suction applied (require means to protect pt’s airway from application of suction, or buildup of positive pressure)

Passive: waste gases proceed passively down corrugated tubing through the room ventilation exhaust grill of the OR (require means to protect pt from positive pressure buildup only)

37
Q

Define a Closed Anesthesia Circuit

A

Fresh gas inflow exactly equal to patient uptake, complete rebreathing after CO2 absorbed, and pop-off closed

Reservoir (Breathing bag) = Yes
Rebreathing = Yes, complete
Example: circle (with pop-off valve closed)

38
Q

Define an Open Anesthesia Circuit

A

No valves, no tubing – pt has access to atmospheric gases

Reservoir (breathing bag) = No
Rebreathing = No
Example: open drop ether, or nasal cannula

39
Q

Define a Semi-Closed Anesthesia Circuit

A

Some rebreathing occurs, fresh gas flow and pop-off settings at intermediate valves

Reservoir (breathing bag) = Yes
Rebreathing = Yes, partial
Example: circle at low FGF

40
Q

Define a Semi-Open Anesthesia Circuit

A

No rebreathing, high fresh gas flow higher than minute ventilation

Reservoir (breathing bag) = Yes
Rebreathing = No
Example: nonrebreathing circuit or circle at high FGF

41
Q

What is the purpose/function of CO2 absorbents?

A

Make rebreathing possible

Lower flows, conserve gases and humidity and prevent respiratory acidosis

42
Q

What determines the amount of rebreathing?

A

Fresh gas flow rate

*increase FGF rates in CO2 absorbent runs out and you can’t get more

43
Q

What is the main component in most CO2 absorbers?

A

Calcium Hydroxide – Ca(OH)2

*hydroxides are added to speed the process

44
Q

What is the chemical reaction (process) of the absorption of CO2 by absorbents?

A

1) CO2 + H2O H2CO3 (Carbon dioxide + Water = Carbonic Acid)
2) H2CO3 + 2NaOH (KOH)* Na2CO3 or K2CO3 + 2H2O + heat (Carbonic acid reacts w/ hydroxides to form either Na or K carbonate and water)
3) Na2CO3 or K2CO3 + Ca(OH)2 CaCO3 + 2NaOH (KOH) (Calcium hydroxide accepts the carbonate to form calcium carbonate and Na or K hydroxide) – come back to the activators which can go back forming a cycle

*KOH is no longer in use as it is implicated with CO and Compound A formation

45
Q

What is soda lime’s (traditional CO2 absorbent) interaction with volatile agents?

A

Soda lime degrades most volatiles – Sevo > Des

Sevo can degrade to form Compound A (toxic to the kidneys) thus flows less than 1-2 L/min for more than 2 MAC hours is not recommended

46
Q

How is Carbon Monoxide an issue with anesthesia machines?

A

More of a problem for Des > Iso&raquo_space; Halo = Sevo

Comes from the dryness (want to make sure you aren’t drying out the CO2 absorbent)
-Higher temps and agent concentrations and low FGF rates will contribute to this

47
Q

What is the flow rate of the oxygen flush valve?

A

35 - 75 L/min

*works if electric fails or if the power is off

48
Q

What is the “vulnerable area” of the anesthesia machine? Why?

A

The low pressure circuit because it is most susceptible to leaks and breaks

  • it is located downstream from ALL safety features except the O2 analyzer
  • if negative pressure leak test is performed incorrectly, a leak in the low pressure circuit will NOT be discovered
49
Q

What would the result of undetected leaks in the low pressure circuit be?

A

A hypoxic gas mixture being delivered or possibly patient awareness (or both)

50
Q

When can internal vaporizer leaks be detected?

A

only with the vaporizer turned ON

*some machines will not detect internal vaporizer leaks unless each vaporizer is turned on and off

51
Q

What tests needs to be completed in the circle system before delivering an anesthetic?

A

Static Test: set APL to 30 cmH2O and it should hold the pressure

Dynamic Test: turn ventilator on and use a test lung (bag) to check for gas flow and valve function

52
Q

What is the most important step in the event of a pipeline crossover?

A

DISCONNECT wall oxygen supply and turn on the backup oxygen cylinder

53
Q

Fail safe valves are NOT FAIL SAFE… a hypoxic gas mixture will result from what?

A
  • Incorrect gas supply
  • Defective or broken safety devices
  • Undetected downstream leaks
  • Inert gasses in the system
  • Dilution by high concentrations of inhaled agents
54
Q

What vaporizer can Desflurane only be administered by?

A

TEC 6 vaporizer

*due to its low boiling point and high vapor pressure

55
Q

What can oxygen flushing during inspiration cause?

A

Barotrauma

*oxygen flushing adds to the patients tidal volume with ascending bellows ventilators

56
Q

What is the purpose of non-interchangeable gas-specific connections to pipeline inlets (DISS) with pressure gauges, filter, and check valve?

A

Prevent incorrect pipeline attachments

Detect failure, depletion, or fluctuation

57
Q

What is the purpose of pin index safety system (PISS) for cylinders with pressure gauges, and at least one oxygen cylinder?

A

Prevent incorrect cylinder attachments

Provide backup gas supply

Detect depletion

58
Q

What is the purpose of the low oxygen pressure alarm?

A

Detect oxygen supply failure at the common gas inlet

59
Q

What is the purpose of minimum oxygen/nitrous oxide ratio controller device (hypoxic guard; Link system)?

A

Prevent delivery of less that 21% oxygen (prevent hypoxic gas mixture)

60
Q

What is the purpose of oxygen failure safety device (shut-off or proportioning device)?

A

Prevent administration of nitrous oxide or other gases when the oxygen supply fails (loss of O2 pressure results in cessation of N2O gas flow)

*only detects pressure not oxygen content so it doesn’t prevent potential hypoxic mixture in the case of pipeline crossover or cylinder w/ wrong gas

61
Q

What is the purpose of oxygen entering the common manifold downstream to other gases?

A

Prevent hypoxia in event of proximal gas leak

62
Q

What is the purpose of the oxygen concentration monitor and alarm?

A

Prevent administration of hypoxic gas mixtures in event of a low-pressure system leak

Precisely regulate oxygen concentration

63
Q

What is the purpose of automatically enabled essential alarms and monitors in anesthesia machines?

A

Prevent use of the machine without essential monitors

*Disabling alarms can be very dangerous

64
Q

What is the purpose of the vaporizer interlock device?

A

Prevent simultaneous administration of more than one volatile agent

65
Q

What is the purpose of an oxygen flush mechanism that does not pass through vaporizers?

A

Rapidly refill or flush the breathing circuit

66
Q

What is the purpose of the breathing circuit pressure monitor and alarm?

A

Prevent pulmonary barotrauma and detect sustained positive, high peak, and negative airway pressures

67
Q

What is the purpose of the exhaled volume monitor?

A

Assess ventilation and prevent hypoventilation or hyperventilation

68
Q

What is the purpose of pulse ox, BP, and ECG monitoring on an anesthesia machine?

A

Provide minimal standard monitoring

69
Q

What is the purpose of the backup battery in an anesthesia machine?

A

Provide temporary electrical power (~30 min) to monitors and alarms in event of power failure

70
Q

What is the purpose of the scavenger system of anesthesia machines?

A

Prevent contamination of the OR with waste anesthetic gases

Scientific Principles (16 decks)

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