Medical Gas Storage and Delivery Systems

Vocabulary flashcards covering medical gas classifications, physical characteristics, production methods, storage cylinder standards, safety systems, and flowmeters based on the lecture transcript.

Laboratory Gases

Medical gases used primarily for equipment calibration and diagnostic testing, such as calibrating arterial blood gas (ABG) analyzers.

Therapeutic Gases

Medical gases administered to relieve symptoms and improve oxygenation in patients suffering from hypoxemia.

Anesthetic Gases

Gases combined with oxygen ($\text{O}_2$) to induce and maintain anesthesia during surgical procedures.

Oxygen ($\text{O}_2$)

A colorless, odorless, transparent, and tasteless gas with a density of $1.429\,\text{g/L}$ at STPD; it is nonflammable but greatly accelerates combustion.

Fractional Distillation

The most common and least expensive method of producing large quantities of medical oxygen by liquefying purified air through compression and cooling, then slowly heating it to boil off nitrogen, yielding at least $99\%$ pure $\text{O}_2$.

Physical Separation

A method of producing oxygen for concentrators using either a molecular sieve (yielding about $90\%$ pure $\text{O}_2$) or a vacuum across a semipermeable plastic membrane (yielding about $40\%$ $\text{O}_2$).

Molecular Sieve

Inorganic sodium aluminum pellets used in oxygen concentrators that absorb nitrogen, trace gases, and water vapor from ambient air to deliver $90\%$ to $96\%$ pure oxygen.

Air

A colorless, odorless, naturally occurring gas mixture composed of $20.95\%$ $\text{O}_2$, $78.1\%$ nitrogen, and approximately $1\%$ trace gases, with a density of $1.29\,\text{g/L}$ at STPD.

Carbon Dioxide ($\text{CO}_2$)

A colorless, odorless gas produced by heating limestone in contact with water; it has a specific gravity of $1.52$, does not support combustion, and requires an FDA purity standard of $99\%$.

Helium (\text{He})

An odorless, tasteless, nonflammable, and physiologically inert gas with a density of $0.1785\,\text{g/L}$ that must always be mixed with at least $20\%$ oxygen for clinical use.

Heliox

A therapeutic mixture of helium and oxygen used to lower gas density, promote laminar flow, decrease the work of breathing, and deliver $\text{O}_2$ past severe upper airway obstructions.

Nitric Oxide (\text{NO})

A colorless, toxic gas that supports combustion and acts as a pulmonary vasodilator; approved for treating infants and adults with hypoxic respiratory failure, though high exposure can cause methemoglobinemia.

Nitrous Oxide (\text{N}_2\text{O})

A colorless anesthetic gas with a slightly sweet odor and taste produced by the thermal decomposition of ammonium nitrate; long-term exposure from leaks presents risks of neuropathy, fetal disorders, and spontaneous abortion.

DOT Type 3A Cylinders

Seamless high-pressure gas cylinders manufactured from carbon steel.

DOT Type 3AA Cylinders

Seamless high-pressure gas cylinders manufactured from a steel alloy tempered for higher strength.

Cylinder Safety Relief Devices

Safety components (frangible metal disks, fusible plugs, or spring-loaded valves) designed to vent excess gas to the atmosphere if cylinder pressure or temperature becomes excessively high.

Frangible Metal Disk

A cylinder pressure relief device that ruptures at a specific elevated pressure (typically breaking at around $3000\,\text{psig}$) to prevent cylinder rupture.

Fusible Plug

A thermal safety relief device used on smaller cylinders that melts at elevated temperatures between $208^\circ\text{F}$ and $200^\circ\text{F}$ to release pressure during a fire or extreme heat.

Spring-Loaded Valve

A safety relief device commonly used on large gas cylinders that opens to vent gas at a set high pressure and reseals once normal pressure is restored.

Filling Density

The ratio between the weight of liquid gas introduced into a cylinder and the weight of water that the cylinder would hold if completely full.

Duration of Flow Formula (Gas Cylinder)

The calculation used to estimate remaining cylinder time in minutes: $\text{Duration (min)} = \frac{\text{Pressure (psig)} \times \text{Cylinder Factor}}{\text{Flow (L/min)}}$

Oxygen Cylinder Factors

Specific conversion factors used to calculate duration of flow for oxygen cylinders: E cylinder = $0.28$, G cylinder = $2.41$, and H/K cylinder = $3.14$.

Liquid Oxygen Expansion Ratio

The ratio by which liquid oxygen converts to gas: $1\,\text{L}$ of liquid $\text{O}_2$ weighs $2.5\,\text{lb}$ and expands to produce $860\,\text{L}$ of gaseous oxygen.

Bulk Oxygen System

A high-capacity system holding at least $20,000\,\text{cubic feet}$ of gas, used by healthcare facilities to store liquid or gaseous oxygen economically and safely at low working pressure.

Zone Valves

Shutoff valves located throughout a facility's central piping system that can be closed to isolate specific areas for system maintenance or during a building fire.

American Standard Safety System (ASSS)

A high-pressure safety indexed connector system designed for large compressed gas cylinders (sizes F through H/K) and their attachments to prevent accidental misconnections.

Pin-Index Safety System (PISS)

A safety indexed connector system for small gas cylinders up to size E, using specific pin positions on a yoke connection (e.g., positions 2–5 for $\text{O}_2$ and 1–5 for air).

Diameter-Index Safety System (DISS)

A safety indexed connector system using specific thread sizes and diameters for low-pressure gas connections ($<200\,\text{psig}$) at station outlets, regulators, blenders, and flowmeters.

Reducing Valve

A device designed to reduce high variable gas pressures from storage cylinders or central lines to a lower, safe, constant working pressure (typically $50\,\text{psi}$).

Flowmeter

A device used to set, regulate, and control the rate of gas flow delivered to a patient in liters per minute.

Regulator

A device that combines a pressure-reducing valve and a flowmeter to simultaneously control both gas pressure and flow rate.

Bourdon Gauge

A fixed-orifice, variable-pressure flowmeter that is not gravity-dependent (ideal for patient transport), but becomes inaccurate when downstream resistance/back pressure is applied.

Thorpe Tube

A variable-orifice, constant-pressure flowmeter attached to a $50\,\text{psig}$ gas source, featuring a tapered glass tube containing a float ball to display actual gas flow.

Pressure-Compensated Thorpe Tube

A gravity-dependent Thorpe tube calibrated at $50\,\text{psig}$ with its needle valve placed distal to the flow tube, preventing back pressure from affecting reading accuracy.

Uncompensated Thorpe Tube

A Thorpe tube flowmeter calibrated at atmospheric pressure with its needle valve placed proximal to the flow tube; downstream restriction causes it to read lower than actual output flow.