Medical Gases Flashcards
Classifying gases: State of matter in cylinder
- Non liquified compressed gas
2. Liquified compressed (only N2O)
Classifying gases: Uses
- Anesthesia
- Therapeutic
- Laboratory
Classifying gases: Flammability
- Non-flammable
- Supports combustion
- Flammable
Compressed Gas NON-liquidified
- Remains a gas at ordinary temps and under pressure of 2000-2500 PSIG
- At very low temperatures becomes “cryogenic liquid”
- Service pressures of common gases at 70 F
- Oxygen= 1800-2400 PSIG
- Nitrogen= 1800-2200 PSIG
- Helium= 1600-2000 PSIG
- Air=1800 PSIG
Compressed Gas Liquified
- Becomes liquid in a container at ordinary temperatures and pressures from 25-2500 PSIG
- Liquid at temperature and service pressure at 70 PSIG:
- CO2: (<88 degrees)= 838 PSIG
- N2O: (<98 degrees)=745 PSIG
- Ethylene: (<50 degrees)=1200 PSIG
- Cycloprone (liquid)= 75 PSIG
Flammability
Non Flammable: will not burn, support, combustion, explode.
-some gases can extinguish flames (CO2)
Combustion supporting: increase the rate and intensity of anything that’s burning or could burn
- combustible material ignited in pure oxygen or nitrous oxide environment may be explosive
- minium of 15 feet from flame
Flammable: can be readily ignited
-explosive in the presence of oxygen
Common cylinder size and capacity of O2
E Cylinder: 660 L at 1900 PSIG (these are on back of anesthesia machine)
H Cylinder: 6900 L at 2200 PSIG
Anesthetic Gases
Air Oxygen N2O CO2 Helium Heliox
Anesthetic Gases: Air
- readily available
- can be compressed from the atmosphere, dried and purified by chemical and mechanical means
- may also be synthetically produced from the already purified major components nitrogen and oxygen
Anesthetic Gases: Helium
- less dense than air- reduces airway resistance and turbulence
- chemically inert, lighter than air, colorless, odorless, non flammable, will NOT support life
- main source is from natural gas wells
Anesthetic Gases: Oxygen
- gas in a cylinder b/c critical temperature is below room temp
- colorless, odorless, tasteless, supports life
- non-flammable, but supports combustion
- liquid at -300 F
- when combined with most elements produces ___ oxides
- most commercial O2 produced by liquefaction and separation
- With is our FIO2 right now? 21%
Anesthetic Gases: HeliOX
- Helium-oxygen mixture
- pre mixed 40% O2 or 20% O2
- reduces airway resistance
- reduces airway fires during laser surgery
Anesthetic Gases: Nitrous Oxide N2O
-Molecular weight: 44
BP: -88 degrees C
-vapor pressure: 39,000
-liquid at room temper because “critical temp” is above room temp
-room temp nitrous oxide condenses into liquid at 747 PSGI
-Full E cylinder contains 1590 L of gas and weighs 20.7 lbs
-cylinder gauge reads 747 PSIG, weighs, 14.2 lbs, contains 250 L and has NO Liquid remaining
-produced by thermally decomposing ammonium nitrate (NH4NO3), a common ingredient used in fertilizers and explosives
Anesthetic Gases: Carbon Dioxide CO2
- colorless, odorless, acidic taste, will NOT support life
- non-flammable and does NOT burn
- solid form (dry-ice) converts from solid to gas at atmospheric pressure and room temp without going liquid
- collected as waste gas from burning of other combustibles, purified and liquified
Regulation of Gas and Cylinders
US Department of Transportation***
Compressed Gas Association
-sets safe standards. no legal authority but compliance through JCAHO
National Fire Protection Association (NFPA)
- no legal authority but JCAHO
- bulk oxygen systems
American National Standards Institute (ANS)
-sets basic performance and safety standards for components of anesthesia machines, ETTs and connectors, pressure and vacuum, and gas pressure regulators
NIOSH and OSHA
-protects workers— ppm in ambient air
Must be less than 25 ppm of N2O in ambient air*
FDA
-standards for medical gases
American Society for Testing and Manufacturing
-technology standards
JCAHO or TJC
-voluntary accreditation
US Pharmacopeia and National Formulary
-purity of medical gases
US Department of Transportation
- regulates the construction and handling of all medical compressed gas cylinders including: design, construction, testing, marking, labeling, filling, storage, handling, maintenance, transportation
- Requires periodic visual inspection, especially for fire or thermal damage: internal illuminati
- Every 5 years cylinders are inspected for: dents, gouges, arc burns, physical signs of stress
- Damaged cylinders may be removed from circulation or deemed unsafe for medical use
Gas Cylinders
- usually chrome molybdenum alloy (alluminum in MRI scanner)
- sized A-J (A and H NOT in medicine)
- E most common in healthcare: 660L at 1900 PSIG
- cylinders tested to 166% service pressure
- tested every 10 years
- stamped with: cylinder specs, individual serial number, manufacturer, date of manufacture, date of retesting
- color coded and labeled
& required DOT Cylinder markings
- DOT type and material
- Serial number
- Purchaser, user, and manufacture “Praxair”
- Manufacturer’s mark
- Manufacturer’s identifying symbol
- Retest data, retester, ID symbol, 110% filling, 10 year test interval
- Neck ring owner’s ID
PSI
PSIG
PSIA
PSI= pounds per square inch
PSIG= pounds per square inch gauge (different between pressure measured and surrounding atmosphere, most gauges will read zero at atmospheric pressure)
PSIA= pounds per square inch absolute psia= psig + local atmospheric pressure
1 ATM= \_\_\_\_ kPa \_\_\_\_ mbar \_\_\_\_ Hg \_\_\_\_ cmH2O \_\_\_\_ Psi
100 kPa (kilopascal) 1000 mbar (milibar) 760 mm Hg (millimeters of mercury) 1030 cm H2O (centimeters of water) 14.7 Psi (pounds pre square inch)
Cylinder pressure gauge: Bourdon Pressure Gauge
- measures pressure of GAS remaining in cylinder
- made of small hollow metal tube, soldered at one end, bent into a curve, and linked to a clockwork
- increase in pressure cause tube to straight, decrease to regain its curve. Movement transmitted to clock mechanism and accompanying scale
- gauges calibrated in kPa but PSI also used
The E cylinder with the highest pressure will_____________
-supply gas to the machine
Cylinder content and pressure
- cylinder pressure will be an indicator of content volume only if the contents are all in the gaseous state (NOT liquid)
- if the contents are partially liquid (like N2O) the pressure will remain constant until the last of the liquid is evaporated, then the pressure will fall rapidly
N2O content
Full: 20.7 lbs, 1590 L, 745 PSIG
No liquid remaining: 14.2lbs, 250 L, 745 PSIG
Nearly empty: 14.1 lbs, 125 L, 350 PSIG
The PISS System
Pin Index Safety System
- Each gas cylinder has it’s own unique PIN system
- 2 PINS in anesthesia machine, 2 holes in cylinder valve
- PINS should NOT allow wrong cylinder to be mounted
- not failsafe though*
FYI: Oxygen Index Pins
N2O Index Pins
Air Index Pins
2,5
3,5
1, 5
Cylinder Safety (10 points)
- only handled by trained personnel
- no oil, grease, lubricants on valves, pressure regulators, gauges, or fittings
- 20F (-7C) < Temp < 130 F (54 C)
- Tight connections to prevent leaks
- Do NOT obstruct pressure relief device
- Do NOT cross use regulators, hoses, etc
- Do NOT use reducer adapters— defeats PISS
- Keep valves closed when not in use
- Valve is the most easily damaged part of cylinder
- DONT CARRY CYLINDER BY ITS VALVE
Open cylinder slowly— why?
-adiabatic heat of compression: open too fast= fire
Pressure Relief Device
rupture disc: under a safety cap and bursts at specific pressures
fusible plug: safety device that melts between 170F and 212 F (constructed of woods metal= bismuth, lead, tin, cadmium)
combo of both
pressure relief valve: spring loaded device that closes when pressure returns to limit
cylinder Yoke
- the cylinder Yoke is where it attaches
- labeled, color coded, PIN indexed
- pressure gauge; check valve to prevent empty cylinder filling from full cylinder, filter for particulates, plug when not in use
Free floating valve
- Oxygen valve opens with pressure and closes with pressure
- this prevents the cross filling of cylinder to cylinder and pipeline O2 from pressurizing cylinders
- the cylinder with the highest pressure will supply O2 to the machine
- if cylinder valve doesn’t open- no gas flows to machine
All machines have at least 1 yoke for:
O2
N2O
Air
First stage regulator
- decrease cylinder pressure to 45 PSIG (intermediate)
- lower than pipeline pressure (prevents cylinder from emptying into pipeline)
- diaphragm valve that covers both yokes
Second stage regulator
- reduces from 45-50 PSIG to 16 PSIG (from intermediate to LOW pressure)
- diaphragm valve only reduces pressure
Oxygen flush valve
- be careful, VERY careful
- only pure O2 @ 35-75L/min flow rate
- pressurized at 40-50 PSIG
- ball and spring valve
- can cause barotrauma
Advantages of central/wall/pipeline oxygen
- large capacity
- economies of sale
- stable, continuous supply
- safety
- Bulk N2O is from a bank of H cylinders in the basement stored in liquid form
Liquid Oxygen supply-safety
NFPA requires: Oxygen cryogenic vessel: -25-50 ft from hospital -25-50 ft from flammable gas storage -50 ft from wooden structures -on asphalt of concrete -fenced -posted "no smoking/open flame"
Diameter Indexed Safety System
DISS:
- located on machine
- quick connect for wall hoses
- each connection is sized “indexed” for a specific gas and will not allow another hose to be hooked up to it
- a check valve in the DISS prevents cylinder gas from escaping the machine through the pipeline hoses
Pipeline Gas Supply to OR
- oxygen and N2o arrives from hospital reservoir at 50 PSIG
- hoses are DISS and color coded (quick connects with pin-like extrusion but NOT PISS)
Colors associated with gases: Oxygen Air N2O Scavenger Suction
oxygen: green
air: yellow
n2o: blue
scavenger: purple/black
suction: white
