Medical Gases, Delivery Systems, Safety Standards, and Equipment Calculations

Responsibility of respiratory therapist regarding medical gases

Ensure a safe, uninterrupted supply of medical gases.

Major categories of medical gases

Flammable, nonflammable, therapeutic, and nontherapeutic.

STPD

Standard Temperature and Pressure, Dry.

ATPD

Ambient Temperature and Pressure, Dry.

Viscosity

The "thickness" of a substance or its resistance to flow.

Equation for density

Density = mass ÷ volume.

Reference conditions for specific gravity

Water at 4°C and 1 atmosphere.

Boiling point

The temperature at which a liquid changes to a gas.

Critical temperature

The temperature above which a substance cannot be maintained as a liquid regardless of applied pressure.

Critical pressure

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

Triple point

The condition at which solid, liquid, and gas phases coexist.

Physical characteristics of medical gases

Boiling point, critical temperature, critical pressure, triple point, solubility, physical state in the cylinder, and specific gravity.

Regulatory agencies for medical gases

DOT/ICC, DHHS, FDA, Bureau of Medical Devices, and OSHA.

CGA

Compressed Gas Association.

NFPA

National Fire Protection Association.

ANSI

American National Standards Institute.

Distinction about medical gases and flammability

Few medical gases are flammable, but many support combustion.

Filling temperature for compressed-gas cylinders

21°C or 70°F.

Standard pressure for filling a compressed-gas cylinder

2015 psi.

Acceptable overcharge for compressed cylinder

Up to 10%.

Filling density for a liquefied gas

Weight of liquid gas added divided by the weight of water the container would hold when full.

FiO₂ corresponding to room air

Approximately 0.21.

FiO₂ corresponding to pure oxygen

1.00.

Density comparison of room air and pure oxygen

Pure oxygen is denser.

Basic physical characteristics of air

Colorless and odorless.

Major gases in air

Nitrogen and oxygen.

Trace gases in air

Argon, carbon dioxide, neon, helium, methane, krypton, and xenon.

Does air support combustion?

Yes.

Is compressed medical air identical to ordinary room air?

No.

Production of medical air

Harvester, filtered, compressed, and delivered.

Commercial method of obtaining nitrogen from air

Fractional distillation of liquefied air.

Sensory characteristics of oxygen

Odorless, tasteless, and colorless.

Is oxygen itself flammable?

No, but it supports combustion.

Physical forms of oxygen storage

Gas or liquid.

Clinical expression of administered oxygen

Flow in L/min or FiO₂.

Implication of an RT assuming patients receive 100% O₂

In some delivery situations, administering a true 100% oxygen concentration can be difficult.

Characteristics of compressed gaseous oxygen

Dry, cool, and pressurized.

Common form of oxygen storage in acute-care settings

Compressed gaseous oxygen.

Average pressure of gaseous oxygen storage

Approximately 2200 psig.

Temperature for gaseous oxygen storage

Approximately 20°C.

Common form of oxygen storage in outpatient settings

Liquid oxygen.

Pressure for liquid oxygen

Approximately 715 psig.

Temperature for liquid oxygen

Approximately −118°C.

Natural production of oxygen

Photosynthesis.

Commercial methods of producing oxygen

Heating metallic oxides, electrolysis of water, fractional distillation, physical separation, molecular sieves, and semipermeable membranes.

Gas separation method after liquefied air

Fractional distillation.

Oxygen production via electrolysis

Electrolysis of H₂O.

Additional gases in healthcare

Heliox, nitric oxide, nitrous oxide, ethylene oxide, nitrogen, carbogen, cyclopropane, and carbon monoxide.

Gases in Heliox

Helium and oxygen.

Emphasized Heliox mixtures

70/30 and 80/20.

Density comparison of Heliox, air and oxygen

Heliox is less dense.

Clinical conditions for Heliox

Upper-airway obstruction and refractory asthma.

Nitric oxide concentration in the atmosphere

Parts per billion (ppb).

Inhaled nitric oxide administration unit

Parts per million (ppm).

Meaning of iNO

Inhaled nitric oxide.

Physiologic action of inhaled nitric oxide

Selective pulmonary vasodilation.

Condition treated with inhaled nitric oxide

Pulmonary hypertension.

Common nickname for nitrous oxide

"Laughing gas."

Therapeutic properties of nitrous oxide

Sedative, anesthetic, and analgesic effects.

Hazards of ethylene oxide

Flammable and highly reactive.

Use of ethylene oxide in healthcare

Sterilization.

Types of medical gas supply systems

Bulk gas system with reserve, alternating supply/cylinder manifold system, and cylinder supply system with reserve.

Gas volume in bulk oxygen system

20,000 ft³.

Forms of storage for bulk oxygen system

Gas or liquid.

Purpose of hospital bulk oxygen system

To supply oxygen throughout the hospital.

Advantages of bulk systems

Less expensive, less prone to failure, less hazardous than individual tanks, and centrally regulated delivery pressure.

Cylinder manifold system definition

A system that connects banks of cylinders to provide a centralized gas supply.

Purpose of reserve cylinder banks

To maintain gas availability if the primary supply is depleted or interrupted.

Effect of increased flow on FiO₂ from an oxygen concentrator

FiO₂ decreases.

Oxygen-concentrator technologies identified

Semipermeable plastic membrane and molecular sieve.

Disadvantage of a semipermeable membrane concentrator

Lower oxygen purity.

FiO₂ from a semipermeable membrane concentrator

Up to approximately 40%.

Oxygen purity of molecular sieve concentrator

About 90–95% oxygen.

High-output oxygen concentrator feature

Two different flow outputs.

Use of high-output concentrator

As a shared or single-use unit.

Regulator of hospital medical-gas piping systems

NFPA.

Gas delivery pressure through hospital piping system

50 psi.

Extensiveness of hospital medical-gas piping labeling

Each floor, hall, and room must have designated labeling.

Alarm function when pipeline pressure drops

A pressure alarm sounds.

Purpose of medical-gas zone valve

To shut off gas to a specific area.

Circumstances for using zone valves

During construction or in case of fire.

Common hospital areas with zone valves

Emergency departments, floor-care areas, ICUs, and operating rooms.

Pipeline pressure annotation near zone-valve example

50 psi.

How a large medical air compressor produces compressed air

A piston draws air into the system and compresses it into a reservoir.

Mechanisms used by small medical air compressor

A diaphragm or turbine.

Gas classified as nonflammable supporting combustion

Oxygen and air.

Gases classified as nonflammable but support combustion

Oxygen and air.

Gases classified as flammable

Cyclopropane and ethylene oxide.

Cylinder color for oxygen

Green; white may also be used.

Cylinder color for helium

Brown.

Cylinder color for nitric oxide

Teal and black.

Cylinder color for nitrous oxide

Light blue.

Gas-mixture cylinder color coding

Combine applicable gas color codes typically supplied in white cylinders labeled with the gas mixture.

Medical gas cylinder type

A high-pressure container.

Steel medical-gas cylinder construction

From seamless steel.

Cylinder designation 3AA

Heat-treated chrome-molybdenum steel.

Material designated by 3A

High-carbon steel.

Material designated by 3

Low-carbon steel.

Material designated by 3AL

Aluminum.

Information indicated by "3AA" marking

The cylinder's construction material/specification.