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RT Corner.net |
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Page 1Characteristics of O2 · O2 is an odorless, tasteless and colorless gas that supports life. While it is not flammable, it does support fire · The normal FiO2 of the atmosphere is 20.9% · While the FiO2 stays the same, the weight of the atmosphere decreases as one moves away from sea level so that the PO2 drops. · The atmosphere is 760 mmHg at sea level & only 226 mmHg at 30,000 feet · O2 is a paramagnetic gas that changes a magnetic field, this fact is the basis for at least one kind of O2 analyzer. · O2 is only slightly more dense than air but less dense than CO2 · O2 is more viscous than air
The density and the viscosity of
various gases change their flows through flow meters.
· States of matter · All substances have 3 states of matter: gas, liquid and solids o These states of matter are changed by temperature alterations o As the molecules move faster in higher temperatures, they start to change from solid to liquid and if they get high enough the fastest molecules move from liquid to a gas state. This movement is called "boiling off." EXAMPLE: ice [solid] melts into water [liquid], which then can move into water vapor [gas]. · Liquid O2 has a boiling point at –183 °C in which it turns into a gas. · Other gases melt at different temperatures & boil off at different temperatures · As a gas is compressed it becomes hotter because of the increase in kinetic energy · When only a few molecules of a liquid move into the gas state below the boiling point, this is known as evaporation · Just as water changes size as it moves through the different states of matter, liquid O2 expands 862 times as it moves into the gas state. · More O2 can be kept at the liquid state than at the gas state. All you have to do is keep the O2 cold enough [below -183 degrees]  Commercial manufacture of O2:
· Purification: an air compressor pulls in air through filters from the atmosphere into the device where it is compressed to 1500 psig, then the resulting heat is dissipated before further compression to 2000 psig. At each stage of compression and expansion the temperature drops and more water leaves the air. Finally the air is cooled by heat exchange [a refrigerator] to -50 °C where the water vapor is frozen out of the gas. Water and a lot of impurities are gone by now. · Liquefaction: air continues to be cooled down by several steps of compression and expansion until it is liquid air which is sent to a distillation tower. · Distillation: as the liquid air moves down the fractional distillation tower, it warms slowly. At different levels, different gases will boil off at their own boiling points. Each gas is captured at this level and sent down a pipe as a pure gas. At one level the purified O2 gases are captured in this manner. The pure O2 is sent to storage cylinders or cooled off into LOX again.
· There are several levels of compressed air [A through J] only J is pure enough for medical uses · Some hospitals use air compressors to pull air in from the environment and compress it to 60 psig for use in the hospital. · Respiratory care equipment is made to operate at 50-60 psig · Air compressors o Some are huge air compressors that power piping systems to the ICU beds, surgery, Neonatal ICU and other selected areas o Other have smaller high pressure air compressors that are used in the hospital and the home to power ventilators between 50-60 psig o A few ventilators have their own built-in air compressors o And still others can work off the hospitals piped in air but have a automatic back up air compressor that kick in when the gas pressure in the wall drops to a critical level o There are tiny air-compressors that use used to deliver SVN medication. These rarely exceed 10 lpm & cannot operate ventilators or flow meters. o The gas is only as clean as it's source · When there are filters/dryers in the air line, all ventilators and other pieces of equipment that interface with the air line need to have their own high pressure filters/dryers to protect the internal structure of the machines from humidity and other impurities in the air lines
· Carbon dioxide makes up a small portion of the atmosphere [only .03%] it is a byproduct of both cellular respiration & incomplete combustion. · If CO2 replaces O2, it will not support life · CO2 is used to power carbonated drinks, in fire extinguishers and as "dry ice" it is used to chill food · In the hospital, CO2 tanks are used to calibrate arterial blood gas machines. For the ABG machine to accurately measure CO2 in the blood, it must be exposed to both high and low level of CO2 for the two-point calibration needed for precise measurement of blood PaCO2. · As PaCO2 levels rise in the bloodstream, the brain responds by increasing both the breathing rate and Vt. The Ve changes will change the PaCO2. Decreased PaCO2 triggers the brain to return the Ve to baseline. · However once the CO2 gets excessively high, the patient becomes confused, then loses consciousness Percentages of medical CO2 used in this country? · Various specific percentages are used for the different blood gas machines. there are generally two tanks of CO2 mixtures, a high and a low percentage. · When delivered to a patient one would mix it with O2 at the following percentages: o 95% 02 / 5% CO2 o 90% 02 / 10% CO2 Why do we not want to use a humidifier when we deliver CO2?
If a new use for CO2 is discovered, you need to know that: · CO2 and water make carbonic acid, so humidified CO2 stings the face. · Deliver it dry with a hand-held none-rebreathing mask · The RCP should not leave the patient · Constantly monitor respiratory rate, heart rate and blood pressure · Stop, if patient losses consciousness · Give for no more than 10-15 minutes · Never give CO2 to a person with chronic hypercapnia
The use of helium as a medical gas: · Helium is a light gas. Its density is only 1/6th of air's density · Because the gas density is so low, the presence of He in the upper airways changes the sound of the vocal cords · The gas can move around upper airway obstructions · Administration of O2 Helium mixtures [Heliox] is used to treat hypoxemia in those persons whose problem is partial upper airway occlusion · Helium is a rare gas; it is distilled from a natural gas that is found only in Texas, in one place in Canada and by the Black Sea. The USA government keeps a monopoly on He because of this. · Helium does not support life so it must be mixed with O2 o 80% He /20% O2 o 70% He/30% O2 o Administered with a non-rebreathing mask Hazards : · Hypoxia. There have been a few occasions where commercial tanks of Heliox separated. The He would rise to the top of the tanks while the more dense O2 would drop. The RCP might need to analyze the O2 before it gets to the patient. · Due to the density of helium, it is a poor transporter of aerosolized medication · Because it is so low in density it impairs the cough
·
Heliox mixtures will not be accurately displayed by a
O2
flow
meter. If one uses the 80/20 mixture, the set flow rate must be multiplied by a factor of 1.8 to get the true flow rate If one uses the 70/30 mixture, the set flow rate must be multiplied by a factor of 1.6 to get the true flow rate
· Because the amount of O2 used in even a small hospital is so huge, the gas is generally piped into the building · Once a clinic's gas reserves reach 20,000 cubic feet, one is now working with a bulk system · Operation of a bulk gas delivery system falls under the rules of the Compressed Gas Association, [CGA], the national Fire protection agency [NFPA] and other agencies dictating state and local building codes · The Joint commission on Accreditation of Healthcare Organizations [JCAHO] plays a big part in the regulation of these systems
· Banks: multiple cylinders attached to each other in a line. Each cylinder must have a check valve between it and the mainline · Check valves: a one-way valve that prevents gas from a single leaky cylinder to deplete the entire system · Headers: connection between two high pressure lines · Main line: pipes that connect the operating supply to the risers and the branches · Risers: pipes that rise between floors · Lateral branches: horizontal pipes that that move out from the riser to the rooms or groups or rooms on each floor · Manual shut off valves: valves that can be shut off by hand by a simple gesture o Manual shutoff valves will be used in case of a fire downstream o Manual shutoff valves will be used in cases of repairs downstream · Zone valves: manual shutoff valves located in branch and riser lines. One could isolate an entire area so that repairs could be done without shutting down the entire system. o Quarter turn to shut off o The tech should be able to do this standing up o Zone valve for every riser and for every branch o Zone valve just upstream for every critical area or life support area o Zone valve for every operating room · Pressure gauges: dial in which one can read the pressure in the line at that point. o Each zone valve will have one o It should be easily read standing up o It should be labeled with the gas it measures Three types of central supply of medical gases · Located outside the building with a control panel protected from the weather · Located in a building outside the main building · Located in a room in the building that is used for that purpose · Alternating supply system or cylinder supply without reserve
Two banks are attached to the main line to the hospital. Each bank must hold 24 hours of O2 for that hospital · Each bank has: o More than two cylinders o Have a check valve before it gets to the main line o Have a pressure regulator o A shut off valve for emergencies · At the main line there is a change-over actuating switch that will automatically switch between the two banks o The one being used is the primary bank and the other is the backup o The changeover is stimulated by a drop in the banks' line pressure o The tanks of the backup bank can now be changed · The alternating system without a reserve is used in small clinics or with the anesthesia gases in larger hospitals
Cylinder supply with reserve supply · Primary & secondary systems are generally liquid O2 with a bank of three or more cylinders as a reserve system · Day to day operations go like this: o The gas deliver alternates between the primary and the secondary systems with the reserve only being used for emergencies such as failure of both the primary and secondary gas systems or for use during repairs to one of these systems o Each primary system has check valves between it and the secondary system and each has pressure relief devices as well as pressure gauges o Reserve tanks have check valves and shut-off valves and a pressure gauge o Some systems have pressure gauges in series as failsafe systems · Bulk systems with reserve: liquid O2 with reserve as smaller liquid or as gas in cylinders o The reserve must be located outside the primary supply location or building o Manually controlled shut off valves are needed · Upstream of all pressure regulators · Pressure pop off valves are set to relieve pressure when it reaches more than 50% of normal
· The hospital should have two air compressors of equal size and each one should be able to deliver 100% of the required air needs. · Each compressor should have its own pressure relief valve, check valves and isolation valves · Compressed air is pressured to working pressure then sent to a cooling area where the water vapor is removed and later to a dryer for further removal. · Medical gas should be clean but not sterile because it is not a drug [per the FDA] Why is O2 stored so often in liquid form? · We can hold 860 times more liquid O2 than gas · There is less exchange of banks · These are usually refilled from delivery trucks with indexed connectors · NFPA regulates the site of liquid O2.
· It is kept cooled to below its boiling point. At –300 °F. · The stainless steel storage tanks are like huge thermos bottles with double walled insulated walls. There is a vacuum layer for added insulation. · As it is needed in the piping system, the liquid O2 flows into coils where it is warmed up by exposure to the elements and the O2 inside the coils gets warmer and liquefies · These coils stay iced over, even in the dead of summer Discuss the piping systems of O2 and compressed air. · Seamless copper or brass pipes · Different gases have different diameters of pipes How often are the pipes labeled? Pipes should be labeled with the gas at least every 20 feet and/ or as it goes through a wall into a room. One should never look up at a pipe without being able to see what gas it contains
· Audible & visual arms are required in every vital area · These must deliver a loud and non-cancelable visual alarm if the operating pressure drops 20% · When the alarm goes off there should be a policy for calling the appropriate maintenance persons who maintain the line. What are station outlets? · The station outlet is the final unit of the supply system. This outlet is where the RCP attaches the flow meter or the high pressure hoses for the ventilators · The working pressure at the station outlet for air would be 60 psig and the working pressure for O2 is 50 psig. · The station outlet will be at the patient bedside · The station outlet could have [1] O2 outlet [2] compressed air out let [3] vacuum outlet · The base block which is equivalent to the face plate of an electrical plug will have clear labels for the gas they contain · Each outlet will have a check valve that only opens up to the flow when there is a high-pressure hose or a flow meter attached to it. o If the male and female parts are not connected there will be no flow o Remember that once these check valves are opened gas can go both ways. A leaky RC device could leak O2 out of the wall or leave the appliance to enter the wall depending on the pressures of the wall and the appliance.
o
If the appliance leaks, the device may need to be disconnected
or the flow meter turned off so that the gas will not be wasted.
· DISS: diameter index safety system: different diameters of the threaded connections interface hoses or devices under 200 psig. o There are 2 specifically sized bore that must fit the shoulders for the connection to make o O2 has a #1240 CGA connection · Quick connects: NCG and Ohio. These connections are faster, because they just plug in with a single motion. These are also connections for hoses and devices under 200 psig o While quicker, these are prone to leaks
· Gas cylinders or tanks are used to store high-pressure gas or gas mixtures at max pressures of 2000 psig. · These are used to supply O2 during transport or to remote areas of the hospital Page 2Construction of the gas cylinder · Medical gas cylinders are constructed of steel, aluminum or chrome-molybdenum o Aluminum tanks are used for transport particularly air transport o For home use o For transferring a patient to a MRI area where magnetized metals are dangerous and forbidden · Cylinders are made by shaping a tube which is seamless · The neck is narrowed then threaded to fit a valve stem · The bottom should be flat enough so that the tank can stand on the floor without support · Some tanks are spun around a mold then sealed with very high heat
· Cylinders are inspected every 5-10 years · The inspector looks for rust, dents and corrosion · The inspector will lightly tap the side of the cylinder with a hammer to listen for the clear tone created by the hammer. This should last 2-3 seconds · The valve stem is removed and the inside is examined with a light for rust.
· The tank is immersed in a water bath while empty. · Then the tank is filled to 3000 psig [remember it is supposed to hold 2000 psig · As the gas enters the cylinder, the excessive pressure will cause weakened tank walls to swell and water will be displaced.
· The inspector will stamp the tank on the shoulder with his personal mark as well as the month and year of the inspection · He will indicate the next testing [5 or 10 years] · He will display the test results [elastic expansion]
· Front of the tank o DOT: department of transportation o 3AA material used in construction o 2015 filling pressure in psig o Size and serial number of the tank o Owner of the tank o Mark of the inspector · Rear of the tank o Mode of construction o Date of inspection o Star means that the tank can be inspected every 10 years o EE is the elastic expansion during testing
· The contents of the tank- the exact gas composition found on the left · Color coded hazard class inside a diamond o Non-flammable [green] o Flammable [red] o Oxidizer [yellow] · Signal words: displayed to denote the seriousness of the gas
· If the gas is poisonous, a second diamond is displayed · List of detailed cautions regarding the contents · The name and address of the manufacturer
· Identification of contents · Perforated tag labeled FULL, IN USE, EMPTY o Pull off the FULL portion once the tank is opened, o Once the tank is used up, pull off the IN USE to leave only the EMPTY sign o Then empties are placed together and returned to the manufacturer for refill
· FDA & DHHS regulates the purity of the gas · DOT regulates the handling and the shipping of tanks
What are the colors of the cylinders holding the gases used in
respiratory care?
Compare the E cylinder to the H cylinder. · While there are many sizes of medical gas tanks, the two most commonly used in the hospital setting are the E and H cylinders for O2. · Size o The E cylinder is the smaller one o The H cylinder is the larger one [10x bigger] · The valve stem o the tops of all cylinders narrow at the shoulders into the neck o the valve stem sits in the neck and when twisted it opens the cylinder for the gas to escape the tank · The E cylinder’s valve stem is opened and closed with a wretch [commonly called a O2 Key or Key] & this opening is flush to the valve stem · The E cylinder’s valve stem fits into a YOKE type of connector to the gas regulator which will control the pressure and the flow of the gas as it leaves the tank · The E cylinder outlet must include an O ring or washer for the regulator to fit without leaking gas · The H cylinder’s valve stem is opened by turning the wheel handle welded onto the valve stem · The H cylinder contains a male connector onto which a regulator's threaded inlet will fit There are two basic types of valve stems
· Packed: direct valve stem uses resilient packing to prevent leaks, these take higher pressures & are cheaper than the diaphragm. It takes two or three turns to open · Diaphragm: indirect valve which raises the stem, raises the diaphragm. It opens with only a quarter turn or a ¾ turn Valve outlets: both E and H cylinders have coverings over the outlets. · Brand new E cylinders have a white plastic covering · H cylinders have an aluminum cover Pressure relief devices: to prevent rupture of the entire cylinder in the case of increased pressures [increased temperatures or over filling] gas tanks contain various types of pressure relief devices · Disc ruptures at high pressure to vent gas · Spring-loaded pressure valves are usually in the larger tanks · Fusible plug which melts at the high temperatures associated with excessive pressure How is the H cylinder opened? The valve stem on the H tank is opened by turning the hand wheel counter clockwise [turn to the left to loosen]
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