Storage and Delivery of Medical Gases

Flashcards covering medical gas characteristics, production, storage, safety systems, and delivery equipment based on Chapter 41 lecture notes.

Laboratory gases

Medical gases used for equipment calibration and diagnostic testing.

Therapeutic gases

Medical gases used to relieve symptoms and improve oxygenation of patients with hypoxemia.

Anesthetic gases

Gases combined with $O_2$ to provide anesthesia during surgery.

Oxygen ($O_2$) Physical Characteristics

Colorless, odorless, transparent, and tasteless gas with a density of $1.4291\,g/L$ at STPD, which is slightly heavier than air ($1.29\,g/L$).

Joule-Thompson effect

A process where purified air is liquefied by compression and then cooled by rapid expansion; used during the fractional distillation of atmospheric air.

Fractional distillation

The most common and least expensive method for producing most large quantities of medical $O_2$.

Molecular sieves

A physical separation method that produces concentrated $O_2$ by absorbing nitrogen, trace gases, and water vapor from the air.

Air Composition

A naturally occurring gas mixture containing $20.95\%$ $O_2$, $78.1\%$ nitrogen, and approximately $1\%$ trace gases.

Carbon Dioxide ($CO_2$) Specific Gravity

At STPD, $CO_2$ has a specific gravity of $1.52$, making it approximately $1.5$ times heavier than air.

Helium (He)

A chemically and physiologically inert gas with a density of $0.1785\,g/L$, which is much less than air.

Heliox

A mixture of $O_2$ and helium used therapeutically to manage severe airway obstruction by making gas flow more laminar.

Nitric Oxide (NO)

A colorless, nonflammable, toxic gas approved by the FDA for the treatment of term and near-term infants with hypoxic respiratory failure.

Methemoglobinemia

A condition resulting from exposure to high concentrations of Nitric Oxide (NO) alone that can cause tissue hypoxia.

Nitrous Oxide ($N_2O$)

A colorless gas with a slightly sweet odor and taste used clinically as an anesthetic agent, produced by the thermal decomposition of ammonium nitrate.

DOT Type 3A

Medical gas cylinders made from carbon steel.

DOT Type 3AA

Medical gas cylinders made from steel alloy that is tempered for higher strength.

Cylinder Safety Tests

Conducted every $5$ or $10$ years, cylinders are pressurized to five thirds of their service pressure to measure leakage, expansion, and wall stress.

Frangible metal disk

A safety relief valve design that ruptures at a specific pressure to vent gas to the atmosphere.

Fusible plug

A safety relief valve design that melts at a specific temperature to prevent excessive tank pressure.

Filling density

The ratio between the weight of liquid gas put into a cylinder and the weight of water the cylinder would contain if full; used to fill liquefied gas cylinders ($CO_2$ and $N_2O$).

Duration of flow (min) formula

$$\frac{\text{Pressure (psig)} \times \text{Cylinder factor}}{\text{Flow (L/min)}}$$

Liquid $O_2$ weight to volume conversion

$1\,L$ of liquid $O_2$ weighs $2.5\,lb$ and produces $860\,L$ of $O_2$ in its gaseous state.

Cracking the valve

The process of opening a cylinder valve slightly to remove dust before attaching a regulator.

Bulk Oxygen System

A system used to meet large $O_2$ needs that holds at least $20,000\text{ cubic feet}$ of gas.

Zone valves

Valves located throughout a central piping system that can be closed for maintenance or in the event of a fire.

American Standard Safety System (ASSS)

A safety indexed connector system specifically for large cylinders and their attachments to prevent accidental misconnections.

Diameter-Index Safety System (DISS)

A safety system for low-pressure gas connectors found at piping outlets, blenders, flowmeters, and vents.

Pin-Index Safety System (PISS)

A safety system for small cylinders (up to size E) using a yoke type connection with specific pin positions ($2-5$ for oxygen; $1-5$ for air).

Reducing valve

A device used to reduce gas pressure to a useable level.

Flowmeter

A device used to control and set the rate of gas flow to a patient.

Bourdon Gauge

A flowmeter that uses a fixed orifice and operates under variable pressures; it is not gravity dependent and is ideal for patient transport.

Thorpe Tube

A variable-orifice, constant pressure flowmeter always attached to a $50\text{-psig}$ source used to measure true flow.

Pressure compensated Thorpe tube

A flowmeter calibrated at $50\,psig$ with the needle valve placed distal to the flow tube to prevent back pressure from affecting accuracy.