Medical Gases and Oxygen Therapy – Part I

Vocabulary flashcards summarizing key medical-gas terms, production methods, storage, safety systems, delivery devices, and hypoxia concepts for RC121 Oxygen Therapy Part I.

Laboratory Gases

Medical gases such as nitrogen, helium, and carbon dioxide used primarily for equipment calibration and diagnostic testing.

Therapeutic Gases

Gases—including air, oxygen, heliox, carbogen, and nitric oxide—administered to relieve symptoms and improve oxygenation in patients with hypoxemia.

Anesthetic Gases

Gases like nitrous oxide that are combined with oxygen to provide anesthesia during surgery.

Non-flammable Gas

A gas that does not burn (e.g., nitrogen, carbon dioxide).

Oxidizing Gas

A non-flammable gas that supports combustion (e.g., oxygen).

Flammable Gas

A gas that burns readily and may be explosive.

Medical Air

A colorless, tasteless mixture of 78 % N₂, 21 % O₂, and 1 % trace gases; non-flammable but supports combustion.

Air Compressor

Device that filters, compresses, and stores atmospheric air for medical use; delivers 50 psig at ≥100 L/min in hospitals.

Fractional Distillation

Most common, least expensive method of producing 99.5 % pure oxygen by liquefying, cooling, and distilling atmospheric air.

Physical Separation

Oxygen production technique that uses molecular sieves or semi-permeable membranes to remove nitrogen from ambient air.

Molecular Sieve

Pellet-filled canister that adsorbs nitrogen, trace gases, and water vapor, providing >90 % oxygen.

Oxygen Concentrator

Home-care device that supplies low-flow oxygen (≈1–5 L/min) via physical separation of room air.

Helium (He)

Inert, non-flammable gas with density 0.1785 g/L; must be mixed with ≥20 % O₂ to support life.

Heliox

Therapeutic mixture of helium and oxygen—common ratios 80/20, 70/30, 60/40—used to decrease airway resistance and WOB.

Heliox Factor

Multiplier (1.8 for 80/20, 1.6 for 70/30, 1.4 for 60/40) applied to an O₂ flowmeter to obtain actual heliox flow.

Actual Heliox Flow Formula

Actual flow = Factor × O₂-flowmeter setting.

Nitric Oxide (NO)

Colorless gas that is a potent pulmonary vasodilator at low doses; treats PPHN and adult ARDS.

Nitrogen Dioxide (NO₂)

Toxic brown gas formed when NO contacts air; causes chemical pneumonitis and pulmonary edema.

Nitrous Oxide (N₂O)

Sweet-smelling anesthetic gas (‘laughing gas’) that supports combustion; chronic exposure may cause neuropathy and fetal risk.

Carbogen

Older therapeutic mix of 5–10 % CO₂ with oxygen, formerly used for singultus and atelectasis; now rarely used.

Medical Gas Cylinder

High-pressure steel or aluminum container for storing compressed or liquid gases under DOT regulation.

DOT-3AA

Seamless chrome-moly steel cylinder rating that allows filling to 2015 psig (10 % overfill permitted).

Cylinder Color – Oxygen

Green body (white internationally) identifies pure oxygen cylinders.

Cylinder Color – Carbon Dioxide

Gray cylinder designates carbon dioxide.

Cylinder Color – Helium

Brown cylinder indicates helium.

Cylinder Size E

Portable 15-lb cylinder holding ~622 L O₂ at 2200 psig; uses post valve and yoke connector.

Cylinder Size H/K

Large 135-lb cylinder holding ~6900 L O₂ at 2200 psig; uses threaded valve outlet.

psi / psig

Pounds per square inch (absolute) / gauge; psig reads zero at atmospheric pressure.

Standard Working Pressure

Uniform 50 psig delivered by hospital pipelines and regulators to respiratory equipment.

Cylinder Duration Formula

Minutes of gas = (Gauge pressure × Tank factor) ÷ Flow (L/min).

Tank Factor – E

Conversion factor 0.28 L/psi used in duration calculations for E cylinders.

Tank Factor – H

Conversion factor 3.14 L/psi used in duration calculations for H/K cylinders.

ASSS (American Standard Safety System)

Threaded connector system preventing misconnections on large cylinders (>E size).

DISS (Diameter Index Safety System)

Low-pressure (<200 psig) male/female connectors for wall outlets, flowmeters, and ventilators.

PISS (Pin Index Safety System)

Yoke with two pins (e.g., holes 2-5 for O₂) that mates only with correct small cylinder (E or smaller).

Reducing Valve

Device that lowers high cylinder pressure to a constant 50 psig working pressure.

Flow Restrictor

Fixed-orifice device delivering preset low flows (0.5–3 L/min); simplest and least expensive flowmeter.

Bourdon Gauge

Fixed-orifice, variable-pressure flowmeter paired with a pressure-reducing valve; ideal for transport; reads high if downstream pressure increases.

Thorpe Tube

Variable-orifice, constant-pressure flowmeter with tapered glass tube and float; must stay upright; measures true flow.

Frangible Disk

Burst disk that ruptures at a set pressure to vent a cylinder and prevent explosion.

Fusible Plug

Lead/metal plug that melts at a specified temperature, releasing gas on small cylinders if overheated.

Spring-Loaded Relief Valve

Valve that opens against spring tension at high pressure—used on large cylinders and bulk systems.

Pascal’s Law

Pressure applied to a confined fluid is transmitted equally in all directions; explains equal cylinder pressure readings.

Hypoxemia

Abnormally low arterial oxygen tension (low PaO₂).

Hypoxia

Inadequate tissue oxygenation for cellular metabolism.

Hypoxic (Hypoxemic) Hypoxia

Tissue hypoxia caused by low PaO₂ from hypoventilation, V/Q mismatch, shunt, diffusion defect, or high altitude.

Anemic Hypoxia

Normal PaO₂ but reduced oxygen-carrying capacity due to low Hb, hemorrhage, COHb, or MetHb.

Circulatory Hypoxia

Inadequate tissue oxygenation from low or stagnant blood flow; seen in shock or AV shunts.

Histotoxic Hypoxia

Cells unable to use delivered oxygen, often from cyanide poisoning.

Zone Valve

Shut-off valve in hospital piping that isolates sections for fire or maintenance.

Liquid Oxygen (LOX)

Pale blue, cryogenic form of O₂ stored below –181 °F; 1 L LOX equals 860 L gaseous O₂ and weighs 2.5 lb.