common medical gases
- oxygen
- air
- carbon dioxide
- helium
- nitrous oxide
- nitric oxide
- He/O2 mixtures
- O2/CO2 mixtures
less common medical gases
- ethylene
- cyclopropane
- nitrogen
- O2/CO2 mixtures
- He/O2 mixtures
oxygen
- colorless, odorless, tasteless, and transparent
- non-flammable, but greatly accelerates combustion
- density of 1.429 g/L
oxygen production
- chemical method
- fractional distillation
chemical methods
can be used for production of small quantities of oxygen (i.e. electrolysis of water)
fractional distillation
- produces mass quantities of oxygen
- less expensive method
- used to produce oxygen in hospitals for medical purposes
process of fractional distillation
1. air is filtered to remove all dust and impurities
2. gas is then dried to remove all water
3. gas is then compressed to 200 atm.
4. heat caused by compression is then removed by heat exchangers and temperature returns to ambient
5. gas is then decompre
physical separation
principle use in oxygen concentration used in home oxygen therapy
- sieve method
- membrane method
air
- odorless and colorless
- naturally occurring -- 20.95% oxygen, 78.1% nitrogen, and less than 1% trace gases
- density of 1.29 g/L
production of medical grade air
large medical air compressors
- used to provide high flow rates of air at 50 psig
- motor drives a piston in a compression cylinder which draws air through a filter
- air then goes into reservoir tank
- pressure in the reservoir tank is kept higher than d
small air compressors
- for home use to drive small volume nebulizers for medication administration
- usually either a diaphragm or a turbine to compress the air
- do not have a reservoir
- can produce flows of about 6 liters/min
carbon dioxide
- colorless and odorless
- non-combustible
- 1.5 times heavier than air
- cannot support life
production of carbon dioxide
- heating limestone and water
uses of carbon dioxide
- treat hiccups
- treat atelectasis
- prevent complete wash out of CO2 during cardiopulmonary bypass
- treat hypoxic respiratory failure in the new born
- diagnostic purposes (i.e. calibrate blood analysis)
helium
- colorless and odorless
- non-flammable
- density of -.1785 g/L
- cannot support life
production of helium
fractional distillation of natural gas
uses of helium
- large airway obstruction
nitrous oxide
- colorless, slightly sweet taste and odor
- can support combustion
- cannot support life
production of nitrous oxide
thermal decomposition of ammonium nitrate
uses of nitrous oxide
- anesthetic
nitric oxide
- colorless and toxic
- non- flammable and supports combustion
production of nitric oxide
oxidation of ammonia
uses of nitric oxide
- term and near term infants with hypoxic respiratory failure or mechanical ventilation
storage of medical gases
typically stored in high pressure cylinders or large bulk systems
gas cylinders
- constructed of high quality, heat treated, and tempered alloy steel (chrome molybdenum)
cylinder markings
front:
- line 1 -- Department of Transportation (DOT)
- line 2 -- cylinder serial number
- line 3 -- ownership mark
- line 4 -- manufacturers mark
back:
- line 1 -- original hydrostatic test date
- line 2 -- material used to construct cylinder
- line 3 --
cylinder color codes
- green -- oxygen
- yellow -- medical air
- gray -- carbon dioxide
- blue -- nitrous oxide
- brown -- helium
- mixtures -- color combination
large cylinders
- sizes G, H/K, M, and N
- use hexagonal nut fitting
- compressed gas outlet and inlet safety fittings
- may have direct or indirect acting valves
- cylinder safety relief valves
- American Standard Safety System ( @#!*% )
cylinder safety relief valves
- frangible disk
- spring loaded valve
- fusible plug
frangible disk
ruptures at specific pressure
spring loaded valve
opens at about 5% < than cylinder bursting pressure
fusible plug
made of woods metal with melts at 150-170 degrees Fahrenheit
small cylinders
- sizes E through AA
- utilize yoke type connections
- pin index safety system ( @#!*% )
- typically use fusible plug as pressure safety relief
sieve method
- air is passed through sieve beds of material that removes nitrogen, trace gases and water vapor
- able to produce a mixture of >90% oxygen
- the higher the flow rate delivered, the lower the concentration of oxygen
- maximum flow is approximately 5-10 l
membrane method
- air forced through a membrane which allows oxygen and water to pass through at a higher rate
- able to produce about a 40% mixture
cylinder key
wrench
measuring cylinder contents
because cylinders can be either completely gas filled or gas and liquid filled.
- different methods are needed to measure cylinder contents
cylinder factors
- H cylinder -- 3.14
- G cylinder -- 2.41
- E cylinder -- 0.28
- D cylinder -- 0.16
- K cylinder -- 3.14
cylinder storage
- store in racks or chain to wall
- do not store combustible material in vicinity of cylinders
- store away from sources of heat
- store flammable gases separately from gases that support combustion
- keep cylinder cap in place if cylinder is not in use o
cylinder use
- secure cylinders at patient's bedside (cart)
- do not use flammable materials (e.g. oil) on regulators, cylinders, fittings, or valves
- "crack" or open cylinder valve slightly to remove dust before attaching regulator
- post "NO SMOKING" signs when oxy
bulk/gas oxygen systems
large facilities will have high oxygen usage
- systems usually hold about 20,000 cu. ft. (566,000 liters of gas)
- may be stored in gas or liquid form
bulk system advantages
- initially expensive, cheapest in the long run
- less prone to interruption
- eliminate hazards and storage of large numbers of large cylinders
- centrally controls system pressure
- operate at low pressure 50-70 psi
- safety standards by NFPA (National
gas supply systems
three types:
1. Alternating supply cylinder manifold
2. Cylinder supply system with reserve supply
3. Bulk liquid system
alternating supply cylinder manifol
- made up of H/K cylinders
- automatically switches banks when pressure decreases to a preset level
- empty bank is changed and becomes reserve bank
- best for small facilities or with nitrous oxide
cylinder supply system with reserve supply
- consists of primary, secondary supply, and reserve supply
- when the primary supply is depleted, system automatically switches to secondary
bulk liquid system
- small amount of liquid provides large amount of gas; very economical and minimizes space needed
- large tanks at low pressure -- 250 psi
- essentially large thermos bottles having inner and outer steel shells separated by a vacuum
- attached vaporizer c
central piping systems
utilized in hospital
- main from bulk oxygen feed system
- main goes to riser(s)
- risers are used to feed floors
- zone values between riser and floor/wing
- therapists must show where the zone valves are for each floor/unit they work on
safety indexed connector systems
- American Standard Safety System ( @#!*% )
- Pin Index Safety System ( @#!*% )
- Diameter Index Safety System (DISS)
American Standard Safety System ( @#!*% )
- used for large gas cylinders (above E)
- high pressure fitting (>200 psi)
- typically hex nut with threads
- not perfect system because some gases share threads
- varies thread diameter bore, threads per inch and right or left handed threading
Pin Index Safety System ( @#!*% )
- used for small gas cylinders (below E)
- high pressure fitting (>200 psi)
- yoke containing pins fits over valve stem
- two pins per gas
- because the pins overlap, there are only 10 possible combinations
Diameter Index Safety System (DISS)
- low pressure fitting (>200 psi)
- regulator outlets, station outlets, and inlets of RT equipment
- 12 different connections
quick connect systems
- typically used at station outlets
- allows for quicker connections
- are indexed by gas to prevent accidental misuse
- may require more maintenance (shutting down unit)
gas pressure and flow regulators
- pressure reducing valves
- flow meters
- flow restrictor
- Bourdon guage flow meters
pressure reducing valves
- takes pressure fro cylinder pressure to working pressure (50 psi)
- can be done in one or multiple stages
- can be preset or adjustable
- can be multistage
flow meters
- allow rate of gas flow to patient to be set and controlled
- calibrated to operate at 50 psi
- common types -- restrictor, Bourdon gauge, and Thorpe tube
flow restrictor
- simplest and least expensive flow meter device
- consists of a fixed orifice calibrated to deliver a specific flow at a constant pressure
- vary the flow by varying the size of the orifice the gas flows through
Bourdon guage flow meters
- always used in combination with adjustable pressure-reducing valve
- uses fixed orifice but operates under variable pressures
- not gravity or position dependent; ideal for patient transport
- not accurate when pressure distal to orifice changes
multistage pressure reducing valves
one or more single stage valves set up in a series
- reducing to working pressure in more than one step
multistage pressure reducing valve advantages
- more precision -- gradual pressure reduction
- produces smoother gas flow
how to find psi
divide liters by facor
how to find liters
multiply psi times factor
how to find l/min
- convert duration to minutes (hrs. x 60 + number of minutes)
- divide liters by number of minutes
how to find duration
- divide liters by l/min
- divide number of hours by 60
- multiply number of minutes by 60