Storage and Delivery of Medical Gases

Vocabulary flashcards highlighting essential terms and definitions from the lecture on medical-gas storage, supply systems, and delivery equipment.

Laboratory Gases

Medical gases used primarily for equipment calibration and diagnostic testing.

Therapeutic Gases

Medical gases administered to relieve symptoms and improve oxygenation in hypoxemic patients.

Anesthetic Gases

Gases combined with oxygen to provide anesthesia during surgical procedures.

Oxygen (O2) – Physical Properties

Colorless, odorless, tasteless gas; density 1.429 g/L at STPD; slightly heavier than air and poorly soluble in water.

Oxygen – Combustion Effect

Non-flammable but greatly accelerates combustion; burning speed rises with higher O2 concentration or pressure.

Fractional Distillation

Most common, least expensive industrial process that liquefies and distills air to separate and collect large quantities of medical oxygen.

Joule-Thompson Effect

Cooling that occurs when a compressed gas expands rapidly—critical step in fractional distillation of air.

Molecular Sieve

Physical separation device that absorbs nitrogen, trace gases, and water vapor to concentrate oxygen.

Oxygen Concentrator (Membrane)

Device that pulls ambient air through a semipermeable plastic membrane, producing concentrated oxygen.

Medical Air – Composition

20.95 % O2, 78.1 % N2, ~1 % trace gases; density 1.29 g/L at STPD.

Carbon Dioxide (CO2) – Properties

Colorless, odorless gas; specific gravity 1.52; does not support combustion; FDA purity 99 %.

CO2 – Clinical Uses

Commonly used in gas mixtures for calibrating blood-gas analyzers and various laboratory diagnostics.

Helium (He) – Properties

Odorless, tasteless, inert gas with very low density (0.1785 g/L); must be mixed with ≥20 % O2 for clinical use.

Heliox

Therapeutic mixture of helium and oxygen that lowers airway resistance and work of breathing in severe obstruction.

Nitric Oxide (NO)

Colorless, non-flammable, toxic gas approved to treat term and near-term infants with hypoxic respiratory failure.

Nitrous Oxide (N2O)

Colorless gas with slightly sweet smell; anesthetic agent that must be mixed with oxygen; chronic exposure risks include neuropathy and fetal disorders.

DOT 3A Cylinder

Seamless carbon-steel gas cylinder classification by the U.S. Department of Transportation.

DOT 3AA Cylinder

High-strength steel-alloy gas cylinder tempered for higher pressure capacity.

Cylinder Shoulder Stamp

Metal stamping that indicates cylinder size, service pressure, serial number, manufacturer, and test dates.

Cylinder Safety Relief Valve

Device (frangible disk, fusible plug, or spring-loaded valve) that vents gas when internal pressure or temperature becomes excessive.

Frangible Disk

Cylinder relief component that ruptures at a preset pressure to release gas and prevent explosion.

Fusible Plug

Relief device that melts at a specific temperature, venting gas if the cylinder overheats.

Spring-Loaded Valve

Relief valve that opens at a set high pressure and reseats after pressure normalizes.

Filling Density

Ratio of the weight of liquefied gas in a cylinder to the weight of water that would fill the cylinder 100 %.

Cylinder Factor

Conversion constant (L/psig) used with specific cylinder sizes to calculate remaining gas volume.

Compressed-Gas Content Rule

For gas cylinders, internal pressure is directly proportional to the volume of gas remaining.

Liquid-Gas Content Rule

For liquefied-gas cylinders, pressure does not correlate with content; weight is required to gauge remaining volume.

Liquid Oxygen Conversion

Every 1 L of liquid O2 (2.5 lb) produces approximately 860 L of gaseous oxygen.

Cylinder Cracking

Momentarily opening a cylinder valve to blow out dust before attaching a regulator.

Cylinder Storage Temperature

Cylinders must be kept below 125 °F (52 °C) and away from heat sources.

ASSS (American Standard Safety System)

Connector system that prevents misconnections on large high-pressure cylinders (H, G, etc.).

PISS (Pin-Index Safety System)

Yoke-type connector system for small cylinders (size E and smaller); pin positions uniquely identify each gas (e.g., 2-5 for O2).

DISS (Diameter-Index Safety System)

Threaded connector system for low-pressure (≤200 psi) gas outlets such as wall piping and ventilator inlets.

Bulk Oxygen System

Centralized storage containing ≥20,000 ft³ of oxygen in gas or liquid form for healthcare facilities.

Cylinder Manifold System

Alternating supply of banked cylinders that automatically switches to a reserve bank when the primary bank empties.

Bulk Liquid O2 with Reserve

Most common hospital system: main liquid-oxygen tank plus backup supply for economy and safety.

Central Piping Working Pressure

Piped medical gases are reduced to a standard 50 psi at the source for delivery to all outlets.

Zone Valve

Shut-off valve placed throughout piping to isolate sections during maintenance or emergencies such as fires.

Quick-Connect Outlet

Bedside connection that allows instant attachment of gas hoses; keyed or shaped specifically for each gas type.

Pressure-Reducing Valve

Device that lowers high cylinder pressure to a usable level for patient care equipment.

Regulator

Combination device that controls both gas pressure and flow from a cylinder or pipeline source.

Flow Restrictor

Fixed-orifice, constant-pressure device that delivers a specific flow based on resistance principles.

Bourdon Gauge

Fixed-orifice flowmeter paired with an adjustable pressure-reducing valve; not gravity-dependent, ideal for transport but sensitive to downstream pressure changes.

Thorpe Tube

Variable-orifice, constant-pressure flowmeter attached to 50 psi sources; measures true gas flow.

Pressure-Compensated Thorpe Tube

Thorpe tube calibrated at 50 psi with the needle valve distal to the flow tube; back-pressure does not affect accuracy but device is gravity-dependent.

Uncompensated Thorpe Tube

Thorpe tube with the needle valve proximal to the flow tube; back-pressure causes the meter to read lower than actual flow.

Integrated Oxygen Cylinder

Cylinder with built-in regulator and flowmeter; alerts when remaining duration is <15 min and removes need for separate wrenches.

Helium – Low Density Benefit

Greatly reduces airway resistance and encourages laminar flow, lowering work of breathing in obstructed airways.

Methemoglobinemia (NO Exposure)

Condition in which hemoglobin is oxidized, impairing oxygen delivery; high nitric-oxide exposure can cause it.

Neuropathy Risk (N2O)

Long-term nitrous-oxide exposure may lead to nerve damage and reproductive issues.

Cylinder Duration Formula (Gas)

Minutes = (Pressure [psig] × Cylinder Factor) / Flow (L/min).

Bulk-Supply Failure Response

Identify affected patients, provide portable cylinders or bag-mask devices, and activate backup liquid or cylinder manifold source.

Flow-Resistance Equation

V = (P1 − P2) / R; defines flow through a fixed orifice in a flow-restrictor device.

Cylinder Transport Rule

Use a cart with a securing mechanism and keep protective caps in place; never drop, drag, or roll cylinders.

Filling Compressed Gas Cylinders

Normally filled to their service pressure (stamped on shoulder) at 70 °F; may be filled to 110 % with DOT approval.