Week 3 - Cylinders/Pipelines and Breathing Circuits Flashcards
1
Q
What are the methods of gas classification?
A
- State of matter in cylinder (non-liquified compressed gas or liquified compressed)
- Uses (anesthesia, therapeutic, laboratory)
- Flammability (non-flammable, supports combustion, flammable)
2
Q
Compressed Gas (Non-liquified) vs Compressed Gas (Liquified)
A
Compressed Gas Non-Liquified: remains a gas at ordinary temperatures and under pressure of 2000 - 2500 psig (at very low temp become “cryogenic liquids”)
Compressed Gas Liquified: becomes liquid in a container at ordinary temperatures and pressures from 25 - 2500 psig
3
Q
What are the service pressures of common gases at 70*F?
A
Oxygen = 1800 - 2400 psig Nitrogen = 1800 - 2200 psig Helium = 1600 - 2000 psig Air = 1800 pisg
4
Q
What temperature and service pressures are the liquified compressed gases?
A
Carbon Dioxide (<88*) – 838 psig
Nitrous Oxide (<98*) – 745 psig
5
Q
What are the levels of flammability?
A
- Non-Flammable: will NOT burn, support combustion, explode (some gases can extinguish flames)
- Combustion Supporting: increase the rate and intensity of anything that’s burning or could burn, combustible material ignited in pure O2 or N2O environment may be explosive, minimum of 15 ft from flame
- Flammable: can be readily ignited, explosive in the presence of oxygen
6
Q
What are the common cylinder sizes and capacities for O2?
A
E cylinder – 660L, 1900psig
H cylinder – 6900L, 2200 psig
7
Q
What are the anesthetic gases supplied in cylinders and pipelines?
A
Air Oxygen Nitrous Oxide Carbon Dioxide Helium Heliox
8
Q
Properties of Anesthetic Gases – Air
A
- 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
9
Q
Properties of Anesthetic Gases – Helium
A
- Chemically inert, lighter than air, colorless, odorless, nonflammable, will NOT support life
- Main source is from natural gas wells
10
Q
Properties of Anesthetic Gases – Oxygen
A
- Gas in a cylinder because 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 produce ___oxides
- Most commercial O2 produced by liquefaction and separation
11
Q
Properties of Anesthetic Gases – HeliOx
A
Helium-Oxygen mixture
- Pre-mixed 40% O2 or 20% O2
- Reduces airway resistance
- Reduces airway fires during laser surgery
12
Q
Properties of Anesthetic Gases – Nitrous Oxide
A
Molecular Wt: 44 Boiling Point: -88*C Vapor Pressure: 39000
- Liquid at room temp (critical temp is above room temp)
- Room temp N2O condenses into a liquid at 747 psig
- Produced by thermally decomposing ammonium nitrate (common ingredient used in fertilizers and explosives)
13
Q
How many liters does a full E cylinder of N2O hold? How much does it weigh? What does the cylinder gauge read? What about when no liquid remains?
A
Full:
Holds 1590L of gas Weighs 20.7 lbs Gauge reads 747 psig
When NO Liquid remaining:
Contains 250L Weighs 14.2 lbs Gauge will start to read lower than 747
14
Q
Properties of Anesthetic Gases – Carbon Dioxide
A
- Colorless, odorless, acidic taste, will not support life
- Non-flammable and does NOT burn
- Solid form (dry-ice) coverts 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
15
Q
How does the FDA regulate gases?
A
Regulates the supply and sale of medical gases and medical gas delivery systems
16
Q
How does the US DOT regulate gases?
A
Publishes requirements for the manufacturing, labeling, filling, transportation, storage, handling, and maintenance of cylinders and containers for the storage of medical gases
17
Q
How does the Occupational Safety and Health Administration (OSHA) regulate gases?
A
Regulates matters affecting safety and health of employees in all industries, including employee safety when dealing with waste anesthetic gases
18
Q
How dos the US Pharmacopeia and National Formulary regulate gases?
A
Sets standards for purity of medical gases (FDA enforces)
19
Q
What other associations publish safety measures?
A
National Fire Protection Association (NFPA)
Compressed Gas Association (CGA)
Canadian Standards Association (CSA)
International Standards Organization (ISO)
20
Q
What are gas cylinders made of and how are they sized?
A
Usually made of chrome molybdenum (Chromoly) alloy — Aluminum in MRI scanner
Sized from A-J (A & H not in medicine)
E = most common in healthcare
21
Q
What is stamped on the side of a gas cylinder?
A
Cylinder specs Individual serial number Manufacturer Date of manufacture Date of retesting Color coded and labeled
22
Q
What are the 7 required DOT cylinder markings?
A
- DOT type and material
- Serial number
- Purchaser, user, and manufacturer
- Manufacturer’s mark
- Manufacturer’s identifying symbol
- Retest date, retester, ID symbol, 110% filling, 10 year test interval
- Neck ring owner’s ID
23
Q
Psi vs Psig
vs Psia
A
Psi = Pounds per square inch
Psig = Pounds per square inch gauge (difference between measured pressure and the surrounding atmosphere) (most gauges will read zero at atmospheric pressure)
Psia = Pounds per square inch absolute (Psig + local atmospheric pressure)
24
Q
1 atmosphere = ? kPa ? mbar ? mmHg ? cm H2O ? Psi
A
1 atm = 100 kPa 1000 mbar 760 mmHg 1030 cm H2O 14.7 Psi
25
What is the Bourdon Pressure Gauge?
- measures pressure of GAS remaining in cylinder
- made of a small hallow metal tube, soldered at one end, bent into a curve, and linked to a clockwork
- increase in pressure cause tube to straighten, decrease to regain its curve
- movement transmitted to clock mechanism and accompanying scale
- gauges calibrated in kPa but psi also used
26
The E cylinder with the ____ pressure will supply gas to the machine.
highest
27
What is cylinder pressure an indicator of?
indicator of content volume -- only if the contents are all in a gaseous state, NOT a liquid state
If contents is partially liquid, (like N2O) the pressure will remain constant until the last of the liquid is evaporated, then the pressure will fall rapidly
28
What is the Pin Index Safety System (PISS)?
Each gas CYLINDER has its own unique PIN position
- 2 pins in anesthesia machine
- 2 holes in cylinder valve
PINS should NOT allow wrong cylinder to be mounted -- however the system is not failsafe
29
What are the Index Pins for oxygen, nitrous oxide, and air
Oxygen = 2, 5
Nitrous Oxide = 3, 5
Air = 1, 5
30
What are safety regulations for cylinders?
- Only handled by trained personnel
- No oil, grease, lubricants on valves, pressure regulators, gauges, or fittings
- 20*F (-7*C) < Temp < 130*F (54*C)
- Tight connections to prevent leaks
- DON'T obstruct pressure relief device
- DON'T cross use regulators, hoses, etc
- DON'T use reducer adapters-defeats DISS system
- Keep valves closed when not in use
- Valve is the most easily damaged part of a cylinder
- Don't carry by its valve
- Don't drop, roll or store unsecured
31
What are safety regulations for mounting a cylinder to a machine?
- ID cylinder before mounting
- Remove protective cover just before use
- "Cracking" the cylinder briefly before attaching to the yolk- keeps dirt out
- Check for plastic seal washer
- PIN index safety system is there for a reason (no match no mount)
- Open slowly to slow compression of gas within the machine and prevent explosions
- Check for a reading on the pressure gauge
32
What are types of pressure relief devices?
Rupture Disc: under a safety cap and bursts at specific pressures
Fusible Plug: melts between 170*F and 212*F to allow release of pressure (constructed of "woods metal")
Combination rupture disc/fusible plug
Pressure Relief Valve: spring loaded device that closes when pressure returns to limit
33
Where do cylinders attach to the machine?
at the Yoke
- Labeled, color coded, PIN indexed
- All machines have at least one yoke for O2, N2O, and Air
34
What prevents cross filing of cylinder-to-cylinder and pipeline O2 from pressurizing cylinders?
Free Floating/Check Valve
-Oxygen valve opens with pressure and closes with pressure
35
What is the First Stage Regulator for cylinder pressure regulation?
Decreases cylinder pressure to 45 psig (lower than the pipeline pressure)
-This prevents cylinders emptying into the pipeline
Diaphragm valve that covers BOTH yokes
36
What is the Second Stage Regulator for cylinder pressure regulation?
If present it reduces cylinder pressure from 45-50 psig to 16 psig
From intermediate TO low pressure system
37
What is the oxygen flush valve?
- ONLY pure oxygen at 35-75 L/min flow rate
- Pressurized at 40-50 psig (wall or cylinder)
- Ball and spring valve
- May cause barotrauma
BE VERY CAREFUL
38
What are the hazards of cylinders?
- Incorrect cylinder installed
- Incorrect cylinder contents
- Incorrect valve, color, or label
- Damaged valve
- Asphyxia (large quantities of non-oxygen gas discharge could dilute O2 content)
- Fires
- Projectile damage (if cylinder falls valve may break off and you have yourself a missile)
- Contaminated contents
39
What are the advantages of central/wall/pipeline oxygen?
- Large capacity (1cf Liq O2 = 860 cf gaseous O2 = 7.3 million L O2)
- Economies of scale
- Stable, continuous supply
- Safety (space and safety to store thousands of cylinders
40
How is bulk N2O supplied?
From a bank of H cylinders in the basement -- stored in liquid form
41
What are the NFPA requirements for liquid oxygen supply safety?
Oxygen Cryogenic Vessel
- 25-50 ft from hospital
- 25-50 ft from flammable gas or gas storage
- 50 ft from wooden structure
- On asphalt or concrete
- Fenced
- Posted "No Smoking/Open Flame"
42
What is the Diameter Indexed Safety System (DISS)?
- DISS is located on the 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 in that spot
- A check valve in the DISS prevents cylinder gas from escaping the machine through the pipeline hoses
43
At what pressure does oxygen and N2O arrive from the hospital reservoir to the pipeline gas supply in the OR?
50 psig
Hoses are DISS and color coded
44
What are the colors of the pipeline gas supply in the OR in the US?
```
Oxygen = Green
Air = Yellow
N2O = Blue
Scavenger = Purple/Black
Suction = White
```
(other gases available in tanks)
45
What are the hazards of pipeline gas supply?
- Inadequate pipeline pressure
- Leaks
- Excessive pressure
- Alarm problems (failure, absence, disconnection, volume too low)
- Gas contamination
- Crossover (check your FiO2 monitor)
46
What are the functions of the breathing circuit system?
1. Delivers gases (O2, anesthetic gases, etc) from machine to the pt
2. Eliminates CO2 (washout (fresh gas flow) or chemical absorption))
3. Alters temperature and humidity of gases
4. Converts continuous flow from the machine into intermittent flow to and from the pt (inspiratory/expiratory flow)
5. Allows spontaneous, controlled, and assisted ventilation
6. Allows for gas sampling, airway pressure, flow, and volume monitoring
47
What is an ideal breathing circuit?
- Simple
- Delivers intended inspired gas mixture
- Permits spontaneous, manual and controlled ventilation in all size groups
- Efficient, (requiring low fresh gas flow rate, low resistance)
- Protects pt from barotrauma
- Maintains moisture and heat
- Sturdy and lightweight
- Easy removal of waste gases (CO2, excess volatile)
- Easy to maintain
48
What is the significance of resistance for breathing circuits?
- Increases work of pt and/or the ventilator (requires more pressure to produce the same volume)
- Decreases resistance of circuits by ensuring that gas conduction pathways have minimal length, maximal diameter, and without sharp curves of kinks
- The ETT is the point of most resistance as it has the smallest diameter of the circuit
49
Define Rebreathing
To inhale previously respired gases
-CO2 may or may not have been removed (many tend to associate rebreathing with CO2 accumulation)
50
What is mechanical dead space?
volume in a breathing system occupied by gases that are rebreathed without any change in composition (rebreathing CO2 etc)
51
How does fresh gas flow rate affect rebreathing?
Amount of rebreathing varies INVERSELY with fresh gas flow rate
- if FGF > minute ventilation = NO rebreathing (IF scavenging or exhaust of exhaled gases at a point close to the respiratory tract)
- if FGF < minute ventilation = rebreathing to make up the required volume
52
What two factors affect rebreathing in a circuit?
Fresh Gas Flow Rate
Mechanical Dead Space (can be minimized by separating the inspiratory and expiratory gas streams as close to the pt as possible)
53
What are the two main types of circuits?
Circle (typically used): CO2 absorber, unidirectional valves, minimal dead space
Mapelson: no CO2 absorber (FGF must washout CO2), no unidirectional valves
54
What are the effects of rebreathing?
- Rebreathing alveolar gas will cause a reduction in the inspired O2 concentration
- During induction rebreathing will reduce inspired anesthetic gas concentration and prolong induction
- During emergence alveolar concentrations exceeds that of inspired gases so rebreathing will slow agent elimination
- Rebreathing of CO2 will cause an increase in ETCO2 if it is not absorbed
- Rebreathing retains heat and moisture
55
What are the general components of breathing systems?
- Bushings (mounts) (modifies internal diameter)
- Sleeves (modifies external diameter)
- Connectors and Adaptors
- Reservoir Bag
- Breathing Tubes
- Adjustable Pressure Limiting Valve (APL) (Pop-off)
- PEEP valves
- Filters
56
What are APL valves?
- The only gas exit from a breathing system unless a ventilator is being used
- Used to control the pressure in the breathing circuit
- ALWAYS set on OPEN during spontaneous respiration
- Can be used to add CPAP
- Close as needed during assisted respiration to enable gas to be directed to pt
- Isolated from breathing circuit during mechanical ventilation
- ASTM requires that a clockwise motion increases limiting pressure
57
Describe a general Mapleson Breathing System
- No CO2 absorption (FGF washes out CO2)
- No unidirectional valves
- No clear separation of inspired and expired gases
- Rebreathing WILL occur if minute ventilation is less than fresh gas glow rate
- Must monitor ETCO2 to determine optimal fresh gas flow rate
58
Describe a Mapleson A Circuit (Magill/Lack)
Fresh gas flow is at the back, corrugated tubing, APL near patient, bag
Flow dependent mechanical dead space
*Good for SPONTANEOUS breathing only (negative inspiration closes the valve thus doesn't work well for controlled ventilation)
FGF for SV = 70-100 mL/kg/min
FGF for PPV = min 3 x MV
59
Describe a Mapleson B Circuit
Fresh gas flow near patient but distal to APL
Corrugated tubing
Bag
*not in use today
60
Describe a Mapleson C Circuit
Fresh gas flow near patient but distal to APL
No corrugated tubing
Bag (Flow inflating)
*Resuscitation bagging
FGF for PPV = 15 L/min
61
Describe a Mapleson D Circuit (Bain)
Fresh gas flow near patient
Corrugated tubing
APL at back
Bag
*Most efficient for controlled ventilation
FGF for SV = 150-200 mL/kg/min
FGF for PPV = 70-100 mL/kg/min
62
Describe a Mapleson E Circuit
Fresh gas glow near patient
No APL
No Bag
"T-Piece"
-Very uncommon
63
Describe a Mapleson F Circuit (Jackson-Rees)
Fresh gas flow near patient
APL at back
Bag at back and has a mechanism for venting excess gas
*Used for pediatric patients
FGF SV/PPV = 2.5 - 3 x MV
Min 4 L/min
64
What are the advantages of Maplesons?
- Simple, inexpensive, rugged
- Low resistance to breathing
- Lightweight
- Easy to use
- Lower compression and compliance volume losses than circle
- FGF changes = rapid changes in inspired gas concentration
- No problems associated with CO2 absorbents
65
What are the disadvantages of Maplesons?
- HIGH fresh gas flow rates (cold patients, lots of wasted gas)
- Difficult to determine ideal FGF
- Difficult scavenging
- Can't be used with possible MH patient because you may not be able to blow off enough CO2
66
What are the components of a Circle Breathing System?
- CO2 absorption
- Unidirectional valves
- Fresh gas inlet proximal to the APL valve
- APL valve
- Reservoir bag (ventilator) (bag/ventilator switch)
- Gas monitoring
- Airway Pressure/Volume Monitoring
- PEEP valve, Filter, Humidifier
67
How do CO2 absorbers work?
Base neutralizing an acid -- carbonic acid is formed by the reaction of CO2 and water
-Granule size 4-8 mesh, channeling reduces efficiency
68
What are CO2 absorber made of?
- Older absorbents: high amounts of K or Na hydroxides led to CO and Compound A (sevo)
- Newer absorbents don't contain K hydroxide and/or little Na hydroxide
- Today they are mostly calcium hydroxide, No CO formation, little compound A and don't lose color when dry
69
What is the best indicator of an exhausted CO2 absorbent?
FiCO2 monitor
70
What steps do you need to do if using Na or K hydroxide absorbents?
- Turn gas flow and vaporizers off when not in use
- Change absorbent at least weekly
- Do not use fresh gas to dry breathing circuits
- Monitor temperature of cannister (more of an issue when barium hydroxide was used)
71
What is the effect of unidirectional valves?
Increase resistance to breathing
May become incompetent leading to rebreathing (more likely on expiration valve)
72
What are the goals for circle systems?
- Minimize absorbent desiccation
- Max inclusion of FGF in the inspired limb and max venting of alveolar gas in the expiratory limb (results in faster induction/emergence) (important in the use of lower FGF rate)
- Accurate readings from the spirometer monitoring system (placing close to FGF may alter readings -- place close to pt)
- Max humidification of gases
- Minimal dead space
- Low resistance
- Convenient
73
What are the issues with circle systems?
- Increased resistance when compared to Mapelson (Not really been shown)
- Dead space (Not really an issue unless extensions used at Y port)
- Heat and humidity increased
- Gas concentrations -- no rebreathing (when FGF>MV) gas vapor concentration in the inspired mixture are same as those in fresh gas -- rebreathing, use the analyzers (alveolar uptake and diffusion of gases alters the inspired concentrations, use ETCO2 to monitor absorbent)
- Low Flow/Closed Circuit (more economical)
- Cleaning/Maintenance
