Egan's Chapter 37

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Egan's Fundamental's of Respiratory Care, Chapter 37, ninth edition by Wilkins

Nonflammable

Does not burn

Oxidizing

Nonflammable but supportive of combustion

Flammable

Burns readily, potentially explosive

Medical Gases

Therapeutic, Laboratory, Anesthetic

Therapeutic gases

Air, Oxygen, Heliox (Helium/oxygen) Carbon Dioxide, Nitric Oxide

Laboratory gases

Nitrogen, Helium, Carbon Dioxide

Anesthetic gas

Nitrous Oxide (aka, N2O)

Oxygen's density

1.429 g/L (slightly heavier than air[1.29 g/L])

Oxygen solubility

3.3ml dissolves in 100ml of water. Sufficient enough for aquatic life to live

Oxygen Production

Electrolysis of water
Decomposition of sodium chlorate
Fractional Distillation
Physical Separation

Fractional Distillation

most common, least expensive production of O2
several steps

Fractional Distillation 1

First, atmospheric air is filtered to remove pollutants, water and CO2. The purified air is liquefied by compression and cooled by rapid expansion (Joule-Thompson effect)

Fractional Distillation 2

the resulting mixture of liquid O2 & N is heated slowly in a distillation tower. Nitrogen escapes first, then traces gases of argon, krypton and xenon. Remaining liquid O2 is transferred to specially insulated cryogenic (low-temp) storage cylinders

Fractional Distillation 3

Can also convert O2 directly to gas for storage in high-pressure metal cylinders --> is 99.5% pure. (FDA requires 99% minimum)

Physical Separation (method 1)

molecular "sieves" composed of inorganic sodium aluminum silicate pellets are used. Pellets absorb N, trace gases & water vapor from air leaving over 90% O2 for pt. use.

Physical Separation (method 2)

a vacuum is used to pull ambient air through a semipermeable plastic membrane that allows O2 & water vapor to pass through faster than N. Produces O2 mixture of 40%. (called Oxygen concentrators, used in home setting)

Ambient

the air around you; normal air

Air

21% O2; 78% Nitrogen; 1% trace gases;
density of 1.29 g/L (standard for measuring gases)
produced by filtering and compressing atmospheric air

Carbon Dioxide

produced by heating lime stone in contact w/ water. The gas recovered is liquefied by compression & cooling. FDA standard = 99%. Most CO2 used for diagnostic purposes in the clinical lab.

Helium (He)

STPD = 0.1785 g/L; ALWAYS mix w/ at least 20% O2; He/O2 used to manage severe cases of airway obstruction. The low density of He decreases WOB

Nitrous Oxide (N2O)

sweet odor & taste. Used as an anesthetic agent. Depresses CNS; Supports combustion. ALWAYS mix with 20% O2; Produced by thermal decomposition of ammonium nitrate; long term exposure causes neuropathy; 25ppm N2O max

Nitric Oxide (NO)

toxic; supports combustion; Produced by oxidation of ammonia at high temps in presence of a catalyst; approved for infants w/ hypoxic respiratory failure

Gas Cylinder Storage

AA, BB, DD, A-E (small, post valve & yoke connector)
F-H and K (Large, threaded valve outlet)

High pressure relief valves

3 basic designs 1) frangible disk, 2) fusible plug,
3) spring loaded valve
always located in the cylinder valve stems

Frangible Metal Disk

ruptures at specific pressure

Fusible Plug

melts at a specific temperature; found on most small cylinders

spring loaded valve

opens and vents gas at a set high pressure; found on most large cylinders

compressed gases

gas cylinders are normally filled to service pressure at 70F, but can be filled to 10% in excess of service pressure

liquefied gases

gases stored as liquids at room temp; includes CO2 & N2O, filled to a specific filling density.

Filling density

ratio between the weight of liquid gas put into the cylinder and the weight of water the cylinder could contain if full.
filling density for CO2 is 68% & N2O is 55%

Compressed gas cylinder contents

vol. of gas in the cylinder is directly proportional to its pressure at a constant temperature. (e.g. full at 2200psi is half full at 1100 psi)

Liquid gas cylinder contents

measure vapor pressure found above the liquid inside the container. weigh a liquid-filled cylinder to accurately determine the content

Tank Factors

E tank = 0.28
H tank = 3.14
Liquid O2 = 344

Formula Clues

For duration, remember your tank factors!
For total flow remember your tic tac toe graph!

American Standard Safety System (ASSS)

Use this safety system on H and G cylinders

Pin-index Safety System (PISS)

Use this safety system on E cylinders

Bulk Oxygen

can be stored in either gaseous or liquid form; liquid storage most common in hospitals. Cheaper over long term

Gas supply systems

3 types- cylinder manifold system, cylinder supply system w/ reserve supply, and a bulk gas system with a reserve

Cylinder manifold system

H-K size cylinders of compressed O2 in a row (picture a menorah) 1 side has the primary bank and the other a reserve bank; supply O2 from a central location, usually in small hospitals & to supply N2O to Operating Rooms

Cylinder Supply System with a reserve

has a primary, secondary (both liquid) and reserve supply; If the primary runs out, the secondary kicks in until the primary is replaced. The reserve (a high pressure cylinder) kicks in if both primary & secondary fail.

Liquid Bulk O2 System

Used in most large hospitals; must be stored below -181.4F; tanks have less than 250psi. safety valve allows vaporized liquid O2 to escape if warming causes cylinder pressure to increase above a set limit.

Central Piping Systems

gas pressure is reduced in system to standard working pressure of 50psi; runs throughout hospital to wall or station outlets

NFPA

National Fire Protection Association

Zone Valves

found throughout piping system and can be closed for system maintenance or in case of fire

ASSS

standards for threaded, high pressure connections btwn lg compressed gas cylinders (sizes F-H/K) threaded w/ hex nut and connecting nipple.

PISS

up to size E tanks; yoke connections w/ pins that fit on the valve stem

Diameter-index safety system (DISS)

prevents accidental interchange of low-pressure (less than 200psi) medical gas connectors; the green & yellow wall outlets in pt's rooms

Reducing Valve

used for reduction in gas pressure

Flowmeter

used to control gas flow to a patient; if both pressure and flow is needed, a regulator is used

High pressure reducing valves

2 types- single stage and multiple stage

Preset reducing valve

High-pressure gas (2200psi) enters through a valve with the inlet pressure displayed on the pressure gauge.

Adjustable reducing valve

has a valve spring at the bottom to control tension. helps devices adjust that need variable pressures and not the standard 50psi; provides a range between 0-100 psi.

Multiple stage reducing valve

can be preset or adjustable; is functionally 2 single-stage valves working in series; gas is decrease first to 200-700psi and then to 50psi. provide more precise & smooth flow control

Low pressure gas flowmeters

3 categories- flow restrictor, the Bourdon gauge and Thorpe tube

Flow Restrictor

simplest & least expensive flowmeter device; requires a source of constant pressure(50psi); a flow restrictor is a fixed-orifice, constant pressure flowmeter device

Bourdon Gauge

flowmeter that is always used in combo w/ an adjustable pressure reducing valve; uses a fixed orifice; operates under variable pressure; is a fixed orifice, variable pressure device (was on the H tank in class)

Thorpe Tube

connects to wall outlet; always connects to a 50psi source; is a variable-orifice, constant pressure flowmeter device

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