CH.41 Storage and Delivery of Medical Gases Flashcards
Laboratory Gases
–are used for equipment calibration and diagnostic testing
Therapeutic Gases
–are used to relieve symptoms and improve oxygenation of patients with hypoxemia
Anesthetic Gases
–are combined with oxygen to provide anesthesia during surgery
Gas flammability: Inflammable
–gases burn and are rarely used for medical purposes
Gas flammability: Nonflammable
–gases do not burn, but some support combustion
Gas flammability: Oxygen
–is a nonflammable gas; it does not burn and will not explode
–supports combustion, making burning brighter, hotter, and faster
Atmospheric partial pressure (ATPD)
–the physical conditions for a given gas are at ambient temperature and 760 mm Hg pressure without any humidity
STPD
–standard temperature, pressure, and dry
Oxygen (O2)
–colorless, odorless, transparent, and tasteless
– STPD: density of 1.429 g/L, slightly heavier than air, not very soluble in water,
– at room temperature and 1 atm pressure, only 3.3 ml of O2 dissolves in 100 ml of water
–Nonflammable but greatly accelerates combustion
Burning Oxygen
– an increase in O2 percentage at a fixed total pressure
– an increase in total pressure of O2 at a constant gas concentration
–Both O2 concentration and partial pressure influence the rate of burning
Oxygen Production
–O2 is produced through one of several methods
– Most large quantities of medical O2 are produced by fractional distillation of atmospheric air
– Small quantities of concentrated O2 are produced by physical separation of O2 from air
Oxygen: Fractional Distillation
– Most common method
–Least expensive method
Oxygen: Physical Separation
–Method 1: molecular sieves absorb nitrogen, trace gases, and water vapor from air
–provides a concentrated mixture of more than 90% O2 for patient use
–Method 2: use a vacuum to pull air through a semipermeable plastic membrane allows O2 and water vapor to pass through at a faster rate than N2 from ambient air
–This system can produce an O2 mixture of approximately 40%
– called Oxygen Concentrators
–used primarily for supplying low-flow O2 in the home care setting
Producing Oxygen
– Alternative procedure is to convert O2 directly to gas for storage in high-pressure metal cylinders
–Produce O2 that is approximately 99.5% pure
– The remaining 0.5% is mostly N2 and trace argon
–US Food and Drug Administration standards require an O2 purity of at least 99%
Air
– yellow cylinders
– colorless, odorless, naturally occurring gas mixture
–Contains 20.95% O2, 78.1% nitrogen, and 1% trace gases
–At STPD: density is 1.29 g/L
–Medical grade air produced by filtering and compressing atmospheric air
– may be referred to in a medical setting as room air or ambient air
Air
–compressed air is supplied in cylinders that are very similar sized to oxygen cylinders
–Piped compressed air is commonly provided in hospital medical gas system
–smaller, portable air compressors are available for hospital or home use
Carbon Dioxide
– STPD: is a colorless and odorless gas with a specific gravity of 1.52, and 1.5 times heavier than air
– Does not support combustion
–Produce by heating limestone in contact with water
–The FDA purity standard for CO2 is 99%
CO2 mixtures
– Calibration of blood gas analyzers
– Diagnostic purposes in clinical laboratories
Helium (He)
– odorless, tasteless, nonflammable, and chemically and physiologically
– Density of 0.1785 g/L
–Commercially produced from natural gas through liquefaction to purity standards of at least 99%
–Must always be mixed with at least 20% O2
–Therapeutic use: Heliox- mixture of O2 and helium
—– manages severe cases of airway obstruction
—– decreases work of breathing. Lower density. Makes gas flow more laminar..
Nitric Oxide (NO)
–colorless, nonflammable, toxic gas that supports combustion
–exposure to high concentrations alone can cause methemoglobinemia, which can cause tissue hypoxia
–FDA approved for use in treatment of term and near-term infants with hypoxic respiratory failure
Nitrous Oxide (N2O)
– colorless gas with sightly sweet odor and taste
–clinically used as anesthetic agent
–must always be mixed with oxygen
– produced by thermal decomposition of ammonium nitrate
Risks N20
–Long term exposure can lead to neuropathy issues
– Fetal disorders
–Spontaneous abortion
Storage: Gas cylinders
–used to store and ship compressed or liquid medical gases
–design, manufacture, transport, and use of these cylinders are controlled by industrial standards and federal regulations
– Made of seamless steel
—– Classifies by U.S Department of Transportation (DOT)
——DOT type 3A cylinders are made from carbon steel
——DOT type 3AA cylinders are made from steel alloy tempered higher strengh
Gas Cylinders
– color coded and marked with metal stamping on shoulder
–stamping indicates size, normal filling pressure serial number, ownership, and method of manufacturer
–safety tests are conducted every 5 or 10 years
Cylinder safety relief valves
– designed to vent gas to atmosphere if tank is heated
–prevents tank pressure from becoming too high
–basic designs
—— frangible metal disk ruptures at specific pressure
——fusible plug melts at specific temperature
—— spring-loaded valve opens and vents gas at set high pressure
Filling (charging) cylinders
–Compressed gases
—-normally filled to their service pressure (pressure stamped on shoulder) at 70 F
—-approved gas cylinders can be filled to 10% in excess of service pressure
—-liquefied gases
—-includes CO2 and N2O
—-Cylinders filled according to specified filling density
Measuring cylinder content
–Gas-filled cylinders
—-Volume of gas in cylinders is directly proportional to its pressure
–Liquid gas cylinders
—-Pressure does not relate to amount of liquid remaining
—-Only weight of cylinder indicates amount of gas inside
Estimating duration of cylinder gas flow
–Factors affecting duration of flow:
—-gas flow, cylinder size, cylinder pressure at start of therapy
–Formulas:
—-Cylinder factor (L/psig)= Cubic feet (full cylinder) * 28.3 / Pressure (full cylinder) in psig.
—-Duration of flow= Content / Flow: Duration of flow (min)= Pressure (psig) * Cylinder factor / Flow ( L/min)
Fraction of inspired oxygen (FiO2)
–Oxygen consumption will vary depending on set FiO2
–At 100% the total volume is supplied from oxygen tank
–anything less, the oxygen is mixed with ambient air therefore consumption from the tank is less
Liquid oxygen cylinder gas flow
–weight of gas must be known to determine volume of gas in liquid-filled cylinder
–1 L of liquid O2 weighs 2.5 lb and produces 860 L of O2 in its gaseous state
–Amount of gas= Liquid O2 Lb * 860/2.5 lb/L
–Duration of gas (min)= amount of gas in container (L)/ Flow (L/min)
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
–post “No Smoking” signs near storage units
– store liquid O2 containers in cool, well ventilated area
Cylinder use
–secure cylinders at patient’s beside
–do not use flammable materials on regulators, cylinders, fitting, or valves
–“Crack” or open cylinder valve slightly to remove dust before attaching regulators
–post “No Smoking” signs when O2 is used
Safe us of Cylinders
–cylinder markings
–color-coding
–labeling
–standardized testing
–standardized valves
–connection indexing systems
–regulation and standardization of filling and refilling of cylinders
Cylinder Filling Pressure
–Most medical gas cylinder of any size are fille to the same high pressure 2200 to 2500 psig
–Respiratory therapist should practice awareness and lifting precautions whenever handling gas cylinders
Distribution and Regulations
–Primary function of distribution and regulation system is to deliver O2 to beside at useable pressure
Regulators
–contents of full gas cylinders more than 2000 psi
–respiratory equipment calibrated for 50 psi
–preset or adjustable
American Standard Safety System (ASSS)
–For large cylinders and their attachments
–prevents accidental misconnections
Pin-Index Safety System (PISS)
–for small cylinders; up to and including size E, and their attachments
–cylinders have yoke type connections
–exact positions of pins and pinhole vary for each gas: 2-5 for oxygen
2-5 for air
Diameter-Index Safety System (DISS)
– for low pressure gas connectors
–found at outlets of pressure-reducing valves, outlets of central piping system, and inlets of blenders, flowmeter, vents
Reducing Valve
–is used to reduce gas pressure to useable level
–single or multiple stage
Flowmeter
–us used to control flow to patient
Regulator
–is used to control both pressure and flow
Low Pressure Gas Flowmeter: Flow Restrictor
– simplest and least expensive flowmeter device
–consists of fixed orifice calibrated to deliver specific flow at constant pressure
–operation is based on principle of flow resistance
Low Pressure Gas Flowmeter: Bourdon Gauge
–always used in combination with adjustable pressure-reducing valve
–uses fixed orifice but operates under variable pressure
–not gravity dependent, ideal for patient transport
–not accurate when pressure distal to orifice changes
Low Pressure Gas Flowmeter: Integrated Oxygen Cylinders
–includes Grab’n Go System
–eliminates need to separate oxygen tanks, Bourdon gauge regulators, and oxygen keys/wrenches
–flow is selected and oxygen tubing to system can simply be connected to patient
Low Pressure Gas Flowmeter: Thorpe Tube
–functions as flow variable-orifice, constant pressure flowmeter device
–increasing size of orifice increase gas flow
–always attached to 50-psig source
–used to measure true flow
Thorpe tube types: Pressure compensated
–Prevents changes in downstream resistance, or back pressure, from affecting meter accuracy
–calibrated at 50-psig instead of at atmospheric pressure
–flow control needle valve placed after (distal) flow tube
–gravity dependent; not ideal for patient transport
Thorpe tube types: Uncompensated
–calibrated in liters per minute at atmospheric pressure (without restrictions)
–gas from 50-psig source flows into meter at rate controlled by needle valve located before flow tube
Bulk Oxygen
–used to meet large O2 needs of health care facilities
–System hold at least 20,000 cubic feet of gas
–O2 may be stored in gas or liquid form
Advantages of Bulk Oxygen
–far less expensive over long term
–less prone to interruption
–eliminate inconvenience and hazard of transporting and storing large number of cylinders
–eliminate need for separate pressure-reducing valves at each outlet
–safer because they operate at low pressures
Gas Supply Systems: alternating supply system or cylinder manifold
system
–consists of large (normally H or K size) cylinders of compressed O2 banked together in series
–when pressure in primary bank decreases to set level, control valve automatically switched over to reserve bank
Gas Supply
Systems: Cylinder supply system with reserve supply
–consists of primary supply, secondary supply, and reserve supply
–when primary gas supply is depleted by demand, this supply system automatically switches to secondary supply
Gas Supply
Systems: Bulk gas system with reserve
–most commonly used in large health facilities for economic, safety, and convenience reasons
–small volume of liquid O2 provides very large amount of gaseous O2 and minimizes space requirements
Gas Supply
System: safety precautions
–failure of bulk O2 supply can be life threatening to patient receiving O2 or gas powered ventilatory support
–facilities should have second, smaller liquid stand tank or cylinder gas manifold as backup
–staff must be prepared to identify affected patients and move appropriate backup equipment to beside
