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CA-1 > Anesthetic Equipment And Monitors > Flashcards

Anesthetic Equipment And Monitors Flashcards

1
Q

What state is the high pressure section of the anesthesia machine in during normal operation

A
  • it is inactive because
  • the hospital’s central gas supply is the primary gas source for the machine
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2
Q

What is the requirement for auxiliary E cylinder system

A
  • It is required to have at least 1 attachment for an oxygen cylinder to serve as a backup source of oxygen in case of a failure of the hospitals supply source
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3
Q

PISS

A

Pin Index Safety System
- two metal pins arranged on a yoke such that they project precisely ONLY to a specific cylinder type
-prevents medical gas cylinder error

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4
Q

What is the gauge pressure of an E cylinder

A

The pressure above the ambient atmospheric pressure
- it is much higher for all the gases than the hospital supply pressure of 50 - 55psig
- a high pressure regulator reduces variable high pressure in the cylinder to nearly constant pressure output to the pressure section of anesthesia machine

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5
Q

Maximum pressure of oxygen E cylinder

A

2200 pounds per square inch gauge (psig)

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6
Q

Maximum pressure in E cylinder for nitrous oxide N20

A

750 psig

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7
Q

Maximum pressure in E cylinder for air

A

2200 psig

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8
Q

3 points of safe use of auxiliary oxygen E cylinder

A
  1. Checking E cylinder is not part of the automatic machine checkout
    - each cylinder must be manually opened and the gauge at the front of the machine checked
    - this is done by the techs. Don’t worry about in practice for now
  2. Auxiliary E cylinder must be kept closed during normal operation
    - otherwise pipeline failures will not be detected because the low pressure alarm will not sound if tank is already depleted
  3. If suspected pipeline contamination eg N20 and O2 cross over is known
    - back up oxygen cylinder will not flow UNLESS machine is disconnected from pipeline
    - system is designed to preferentially draw from pipeline as long as pressure is adequate
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9
Q

Oxygen cylinder pressure - volume

A
  • are proportional
  • full tank 2200 psig = 625 L
  • 1100 psig = 325 L
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10
Q

N2O pressure - volume

A
  • Full tank of N2O has 750 psig = 1600 L
  • As nitrous oxide gas flows more liquid is vaporized and the pressure of the tank remains the same
  • N20 tank remains 750 psig until there is no more liquid in the tank.
    - at this point pressure will begin to fall
    - tank is already 75% depleted
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11
Q

What is the color coding system for gases in North America
- oxygen
- N20
- Air
- CO2
- He

A
  • oxygen — green
  • nitrous oxide — blue
  • air — yellow
  • carbon dioxide — gray
  • helium — brown
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12
Q

DISS - diameter index safety system

A
  • connector for the termination of pipeline gas supply
  • matching diameter male and female connections for thread and seat connection
    • connectors are mutually incompatible for oxygen air and nitrous oxide

Quick Couplers
- similar system but used mutually incompatible pin system

Both are desirable for cylinders which are moved between locations
- can be plugged together or removed easily with simple twisting motion

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13
Q

What is the function of an oxygen flush valve ?

A

Allows manual delivery of high flow rate of 100% oxygen directly to pts breathing circuit
- employed to overcome oxygen leaks
- employed to rapidly increase inhaled oxygen concentration

Flow from oxygen flush valve bypasses anesthetic vaporizers and enter the low pressure circuit
- at rate of 35 - 75L /min

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14
Q

What is a possible adverse outcome of oxygen flushing during inspiratory phase of positive pressure ventilation

A

Barotrauma
- if the anesthesia machine does not incorporate
- a fresh gas decoupling feature OR
- an appropriately adjusted inspiratory pressure limiter

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15
Q

What happens when the oxygen flush valve is stuck in the fully open position

A
  • barotrauma
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16
Q

What happens when the oxygen flush valve is stuck in the partially open position

A
  • dilution of inhaled anesthetic agent concentration
    • which can result in pt awareness under anesthesia
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17
Q

What are the 2 pneumatic safety features to minimize risk of delivering hypoxic gas mixture when oxygen pressure decreases

A
  1. Oxygen supply failure alarm sensor
    • audible and visual warning
    • can not be shut off until minimum value is restored
  2. Oxygen supply failure protective device = fail safe valve
    • affects flow of other gases when oxygen supply is low
      • it either shuts off the binary valve or
      • reduces the flow of other gases such as nitrous oxide and air
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18
Q

What constitutes the low pressure section of gas supply

A
  • starts at the flow control valves and ends at the fresh gas line
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19
Q

What is an ideal gas

A

A gas in which the particles
- do not attract or repel each other
- take up no space

Ideal gas law
PV = nRT

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20
Q

Dalton’s law of partial pressures

A

The total pressure of a mixture of gas is equal to the sum of the partial pressures of each of the constituting gases

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21
Q

Atmospheric pressure

A

Pressure at sea level and ambient temperature is
- 760 mm Hg = 1 atmosphere = 101 kPa

22
Q

Volume percent

A

% volume occidental by gas relative to the sum of all gases present which is the same as
- the proportion of an individual gas by its partial pressure as a % of the total pressure under idealized conditions in the OR
- eg although the partial pressure of room air in Denver 129 compared to 160mm Hg at sea level due to elevation differences,
- it remains 21% at both altitudes

23
Q

Vapor pressure

A

Pressure effect created by a gas molecule on the walls of its container
- Varies with each gas
- Is dependent on temperature
- Is NOT affected by changes in atmospheric pressure

24
Q

What is Latent heat of vaporization
What are its effects

A

The amount of energy required to change 1 gram of a particular liquid to its vapor at constant temperature during evaporation.
- In a well insulated container energy for vaporization must come from the liquid itself
- this results in
- cooling effect that can reduce significantly reduce vapor pressure

25
Q

What is the boiling point of liquid

How does this relate to desflurane

A

Temperature at which vapor pressure equals atmospheric pressure and liquid boils
- desflurane
- unlike all the other volatile anesthetics boils at close to normal room temp therefore
- has high vapor pressure
- requires special vaporizer for delivery

26
Q

What are the physical properties of Halothane
Include SVP SVC MAC MAPP Boiling point

A
  • Saturated vapor pressure SCP — 243
  • Saturated vapor concentration SVC — 32
  • MAC @ age 40yrs v/v% — 0.75
  • MAPP mm Hg — 5.7
  • Boiling pt @ 1 atm — 50.2 deg C 122.4 F
27
Q

What are the physical properties of Isoflurane

A
  • SVP — 238
  • SVC — 31
  • MAC — 1.2
  • MAPP — 9.1
  • Boiling pt — 48.5 119.3 F
28
Q

What are the physical properties of sevoflurane

A
  • SVP — 157
  • SVC — 21
  • MAC — 1.9
  • MAPP — 14.4
  • Boiling pt — 58.6 deg C 137.3 F
29
Q

What are the physical properties of desflurane

A
  • SVP — 669
  • SVC — 88
  • MAC — 6.0
  • MAPP — 45.6
  • Boiling pt — 22.8 deg C 73 F
30
Q

Why can a variable bypass vaporizer not be used for desflurane (3 reasons)

A
  1. the vapor pressure of desflurane is 669 mm Hg at 20 deg C nearly 1 atm
    • prohibitively high bypass chamber flow rates will be required to dilute the vaporizing chamber output to clinical concentrations
  2. Desflurane is moderately potent which means that the amount of desflurane vaporized over a give time is greater than other inhaled anesthetics
    • the resultant greater cooling will be difficult to compensate for without an external heating source
  3. It’s boiling pt is 22.8 deg C 73 F at 1 atm can be encountered under normal OR conditions
    • if it were to boil in the variable bypass vaporizer, the output will be uncontrollable
31
Q

How does the desflurane blender differ from the variable bypass vaporizer

A
  • it is designed such that the delivered desflurane concentration is relatively stable as barometric pressure drops thus the partial pressure of desflurane is lower
  • the anesthesiologist must therefore compensate by increasing the the set desflurane concentration by a factor equal to the % decrease in barometric pressure relative to sea level
32
Q

Describe the circle breathing system and how it varies from ICU ventilators

A
  • it allows for circular flow by incorporating
    • unidirectional gas flow facilitated by one way valve systems
  • it allows for anesthetic gas to be rebreathed unlike ICU ventilator systems in which exhaled breath is released to the room
    • CO2 must therefore be removed for anesthetic gas to be able to be rebreathed
    • waste gas consisting of excess carrier gas, co2 and anesthetic agent must be
      - scavenged and eliminated
33
Q

Where does dead space begin in the circle breathing system

A
  • it begins with the Y piece and continues on the side connected to the patient
34
Q

What is the adjustable pressure limiting (APL ) valve

A
  • also called the pop off or pressure relief valve
  • operator adjustable valve that vents excess breathing circuit gas to the scavenger system
    - provides control to the breathing system pressure during manual ventilation modes
35
Q

Describe the kind of breathing supported by different positions of the APL or pop off valve

A
  • when fully open : allows for spontaneous breathing at atmospheric pressure
  • when partially closed : spontaneous breathing pt will get CPAP
  • at greater degrees of closure: assisted controlled breaths by manual compression of the bag
  • switching to ventilator mode: excludes = closes APL valve
  • Mnemonic : follows the direction of the eyes
    - when eyes are open pt is awake — APL valve is open pt exhales freely
    - when eyes are closed pt is asleep — APL valve is closed - system is pressurized , gas flows in circle
36
Q

What is the most compliant part of the breathing system

A

The reservoir bag
- distends beyond nominal value at plateau pressure of 60cm H20

37
Q

What are the characteristics of a good CO2 absorbent

A

The ideal CO2 absorbent must
- lack reactivity with anesthetics
- lack toxicity
- have low resistance to airflow
- have minimal dust production
- be low cost
- be easy to handle
- be efficient
- be easy to assess absorbent depletion ie its ability to remove CO2
- be easy to remove discard and replace

38
Q

What are the components of soda lime absorbent

A
  • Calcium hydroxide Ca (OH)2 — which reacts with water to yield carbonic acid
  • Water
  • A small amount of a strong base eg NaOH or KOH — acts as a catalyst
39
Q

What are degradation products and in what context are they formed

A
  • volatile anesthetics interact with strong bases eg NaOH and KOH from Ca(OH)2 based absorbents to form degradation products
  • strong base containing absorbents are extremely desiccated and can degrade inhaled anesthetics to
    - clinically significant levels of carbon monoxide
40
Q

What is compound A

A
  • degradation product of sevoflurane and soda lime
  • is nephrotoxic in rats at concentrations found clinically with breathing circuit
    - no clinical studies indicate association between sevoflurane and post op renal dysfunction
    - sevoflurane warning label
    - should not exceed 2 MAC hrs at flow rates between 1 and 2 L/min
    - flow rates lower than 1L/min are not recommended
41
Q

Why has lithium hydroxide LiOH based absorbents replacing classic soda lime absorbents

A
  • LiOH based absorbents do not require the use of catalysts
  • there is also no risk of the production of
    - compound A or Carbon monoxide
  • it maintains excellent CO2 absorption
42
Q

Describe indicator dye used in conventional absorbents . What are its limitations

A
  • ethyl violet is commonly used
    • when its fresh it is white as the pH exceeds 10 and dye is colorless
    • as absorbent becomes exhausted and pH drops below 10 it becomes purple
    • limitations
      - color reversion: where the purple color reverts back to white due to activity of the catalyst. Making it an unreliable indication
      - modern indicators are therefore resistant to color reversion
43
Q

What is the channeling phenomenon

A
  • absorbent particle size and shape are designed to maximize surface area a reduce resistance to flow
  • smaller size = larger surface area
    - but as particle size decreases there is an increased resistance to flow
    - as particles settle in the canisters small passage ways forms
    - gas flows preferentially through low resistance areas
    - thereby decreasing the factional absorptive CO2 capacity
44
Q

What is low flow anesthesia. List advantages and disadvantages

A
  • there is no universally accepted definition
  • in general means fresh gas flow is less than 1-2L/min
  • advantages
    - dec use of volatile anesthetic
    - improved temperature and humidity control
    - dec environmental pollution
  • disadvantages
    - difficulty in rapidly adjusting anesthetic depth
    - accumulation of degradation products and unwanted exhaled gases : this is theoretical
45
Q

What is a semi open circle system

A
  • high fresh gas flow rate
  • minimal rebreathing
  • high waste gas venting through APL valve
46
Q

What is a semi closed circle system

A
  • significant rebreathing occurs
  • some waste flow is vented through the APL or waste valve of the ventilator
47
Q

What is a closed circle system

A
  • rate of oxygen inflow exactly matches the demand
  • rebreathing is complete
  • no waste gas is vented through the APL valve as it remains closed
  • impractical due to technical demands in for routine use
48
Q

Similarities and differences between mapleson breathing system and circle breathing system

A

Similarities
- accept gas flow supply
- supply pt gas volume from a reservoir
- eliminates CO2
Differences
- have bidirectional gas flow
- lack absorbent
- depend on appropriate rate of fresh gas flow to eliminated C02 and prevent rebreathing :
- which makes it more expensive

49
Q

What is the purpose of a bellows ventilator

A

Acts as a volume reservoir for breathing gas
- rigid airtight housing with bellows
- Inhalation
- pressurized gas flows into housing — bellows are compressed — breathing gas to pt
- exhalation
- bellows are refilled by pts exhaled and fresh gas — excess circuit gas is vented to scavenging system

50
Q

What is the daily check for the anesthesia work set up (mnemonic)

A
  • MS MAIDS
  • Machine
  • Suction
  • Monitors
  • Airway
  • IV
  • Drugs
  • Special Equipment

CA-1 (8 decks)

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