Oxygen and ventilation delivery devices Flashcards
Draw a diagram of a vaccuum insulated evaporator
How is oxygen produced for hospitals?
Fractional distillation offsite delivered as vaccuum insulated evaporators
How is oxygen sourced to hospitals
Vaccuum insulated evaporator storage tanks - vaccuum insulted to keep contents below -160 degrees. It is not acitvaely cooled instead relying on insulation and evaporation to maintain the temperature. - aevaporation uses energy in the form of heat (latent heat of vapourisation) and therefore VIE remain cool
Oxygen critical temperature
-119 degrees
What pressure is oxygen kept under in a VIE system
700 kPa or 7 Bar
How are low and high use situations in hospital handled by the oxygen delivery ssytem
VIE holds oxygen at -160 degrees coincidentally is saturated vapour pressure is the same as the pressure it is held at - if left unvented the pressure rises so there is a vent for relief valve
In high use situations rapid vapourisation cools the oxygen reducing supply, to counteract this a valve is opened allowing liquid oxygen to enter an evaporator at room temperature
Why is oxygen cold coming out of the tap
Latent heat of vapourisation
Liquid oxygen compared ot gaseous oxygen volume
860 times as it vapourises at 20 degrees
What are cylinders of medical gas supplies made of
Chromium molybdenum steel or aluminium
What size culinders are used in medical transfer and anaesthetic gas machines for medical gas supply - what is the cylinder oxygen volume in litres, and weight
E - 5.4kg’ carries 680L of oxygen at 137 Barm 15 degrees
What is the pressure in a medical oxygen cylinder?
13700 kPA or 137 Bar or 2000psi when full at 15 degrees
What is the measurement device for pressure in a medical gas cylinder read of?
Bourdon gauge - pressure is proportional to volume if temperature is constant according to Boyle’s law
Is it possible to compress oxygen into a liquid
No as long as the temperature is above its critical temperature
How is air supplied in hospitals? Draw a diagram
An oxygen concentrator used in a home supply produces what concentrations of gas
Oxygen concentrators produce
concentrated oxygen from air (which
consists of 78% nitrogen, 21% oxygen,
1% argon, and a variable amount of
water vapour). Nitrogen and water
vapour are removed, leaving up to
95% oxygen and 5% argon.
What pressure are piped oxygen and air supplies at
4 Bar
What is the name of the wall connection for medical gas suppliues
Schrader outlets and probes
What should a medical suction system be capable of providing?
What is average minute ventilation at rest for an adult? Why cannot oxygen be supplied at this rate to meet FiO2 100%?
What is required to provide 100% oxygen?
What factors determine FiO2 in variable performance devices?
Volume of the mask (resevoir)
Patients respiraotry dynamics
Seal fo the mask
Oxygen flow
How is a fixed performance device different to a variable performance device
Oxygen air mix at a flow greater than peak inspiratory flow - as this is variable it si not perfect BIT a fixed device can never deliver more than a specific FIO2 - Venturi mask and nasal high flow are examples
How does mouth breathign affect nasal cannulae
During use, the nasopharynx acts an oxygen reservoir. Even if the patient breathes through the
mouth, oxygen will be entrained from the nasopharynx and a majority of studies have shown
that mouth breathing results in either the same inspired oxygen concentration, or a higher
concentration. This effect is unpredictable, however, and therefore nasal cannulae deliver a
variable FiO2.
Draw the venturi mask diagram and explain how it works
Oxygen flows through a central constriction and room air is entrained through the aperture due to a combination fo rthe venturi effect and frictional drag. Venturi effect is a consequecne of the Bernoulli principle whihc states that in order to maintain constant flow a fluid must increase its velocity as it flows through a constriction - this increase in kinetic energy is at a consequence of uts potential energy through a decrease in pressure;. The energy is therefore kept constant
Draw a bag valve mask valve during inspiration and expiration
Between the bag and the mask there is a one way non rebreathing valvbe venting expired gas
Draw and describe a adjustable pressure limiting valve and give a use for it
PEEP valve on a BVM or an APL valve in an anaesthetic gas machine ot provide PEEP
Advantages and disadvantages of an APL valve
What is the law of Laplace
