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Physics RCOA > Gas supplies > Flashcards

Gas supplies Flashcards

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1
Q

Define critical pressure

A

The minimum pressure required to liquefy a gas at its critical temperature

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2
Q

How is O2 supplied to a hospital?

A
  • VIE
  • Cylinder maifolds
  • Portable cylinders
  • O2 concentrators
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3
Q

What are the components of a VIE O2 tank?

A
  • Double skinned steal tank
  • Vacuum of 0.16-0.3 exists between skins
    -Temp -160 - -180
    -O2 is below critical temp (-118) so in liquid form with a saturated vapour at 10bar
  • O2 vapour drawn out of the top
  • Latent heat of evaporation required to vaporise O2 to equilibrium
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4
Q

How does a low demand/warm weather VIE work?

A
  • Reduces the cooling effect of the vaporising process
  • Pressure increases
  • Safety valve opens at 15bar
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5
Q

How does a high demand/cold weather VIE work?

A
  • Insufficient energy to sustain adequate evaporation to meet demand
  • Liquid O2 can be trapped at the bottom of the system
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6
Q

What is the critical temp of NO2? What is its form at room temp?

A

36.4
Liquid & gas

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7
Q

In what form is NO2 inhaled & exhaled?

A

Inhaled: Vapour
Exhaled: Fixed gas

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8
Q

What are the curves of constant temperature called?

A

Isotherms

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9
Q

Describe the isotherm curve at 40 degrees for NO2

A
  • Above critical temp
  • Fixed gas
  • Relationship to Boyle’s law
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10
Q

Describe the isotherm curve at 36.4 degrees for NO2

A
  • At critical temp
  • Sharp inflexion at 73 where liquefaction occurs (critical pressure)
  • Sharp pressure rise with vol decrease as liquids are incompressible
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11
Q

Describe the isotherm curve at 20 degrees for NO2

A
  • Room temp line
  • Steady linear increase as vapour is compressed
  • Plateau in pressure as vol reduction causes liquefaction
  • Sharp rise once all vapour liquefied
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12
Q

How are NO2 cylinders filled?

A
  • Cylinders filled to 75% of the weight of water due to risk of explosion
  • Filling ratio based on weight not vol due to differing densities
  • Cannot use Bourdon pressure gauges
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13
Q

Describe the characteristics of Entonox

A
  • 50:50 NO2 and O2
  • Components separate below pseudo-critical temp of -5.5 degrees
  • To reverse store cylinder above temp to allow diffusion into vapour
  • Store horizontal
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14
Q

What are the characteristics of medical cylinders?

A
  • Checked every 5 years
  • Made of molybdenum
  • Can withstand pressures 65-70% above working pressure
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15
Q

What Mapleson circuits are used in paeds?

A

E & F

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16
Q

What are the key differences in each Mapleson circuit?

A

Where APL, fresh gas inlet & reservoir bag are placed

17
Q

Describe the Mapleson A circuit

A
  • Most efficient in spont respiration
  • Example of Magill & Lack system
  • Dead space too great to use in kids
  • Re-breathing dead space gas & fresh gas at 70%
  • At expiration fresh gas fills bag & dead space gas enters system
  • At pause pressure rises in system to valve opens & alveolar gas leaves
  • At inspiration dead space gas is inhaled followed by fresh gas
18
Q

Why is Mapleson A inefficient in controlled ventilation?

A
  • APL valve partially closed
  • At beginning of expiration reservoir bag almost empty due to high positive pressure when squeezing the bag
19
Q

Describe the Mapleson D circuit

A
  • Least efficient for spont breathing
  • In expiration dead space, alveolar & fresh gas all reach bag
  • In pause fresh gas pushes out alveolar gas through valve
  • In inspiration initially fresh gas but if not enough then dead space & alveolar gas (including CO2) from the bag inhaled
  • Increasing length of tubing does not affect performance
20
Q

What are the advantages of a circle breathing system?

A
  • Minimal equipment dead space
  • Conservation of heat & humidity
  • Ability to remove CO2 & recycle gases
  • Reduction in pollution
  • Minimize fresh gas consumption
21
Q

What are the disadvantages of a circle breathing system?

A
  • Multiple components to maintain & test
  • Potential for leaks
  • If inadequate fresh gas flow then circuit can empty
22
Q

What is the reaction that occurs in the soda lime?

A

Exothermic
Produces 1 mole H2O for every mole CO2 removed
Soda made of calcium hydroxide

23
Q

What is the chemical equation for the reaction in the soda lime canister?

A
  1. CO2 + H20 –> H2CO3
  2. H2CO3 + NaOH. –> H2O + NaHCO3
  3. NaHCO3 + Ca(OH)2 –> H2O + NaOH + CaHCO3
24
Q
A

Physics RCOA (9 decks)

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