1. Chapter 37 Storage and Delivery of Medical Gases

2. Learning Objectives
Describe how medical gases and gas mixtures are produced.
Discuss the clinical applications for medical gases and gas mixtures.
Distinguish between gaseous and liquid storage methods.
Calculate the duration of remaining contents of a compressed oxygen cylinder.

3. Learning Objectives (cont.)
Calculate the duration of remaining contents of a liquid oxygen cylinder.
Describe how to properly store, transport, and use compressed gas cylinders.
Distinguish between gas supply systems.
Describe what to do if a bulk oxygen supply system fails.
Differentiate between safety systems that apply to various equipment connections.

4. Learning Objectives (cont.)
Select the appropriate devices to regulate gas pressure and/or control flow during various clinical settings.
Describe how to assemble, check for proper function, and identify malfunctions in gas delivery equipment.
Identify and correct common malfunctions of gas delivery equipment.

5. Characteristics of Medical Gases
Oxygen (O2)
Colorless, odorless, transparent, & tasteless
Has density of g/L
3.3 ml of O2 dissolves in 100 ml of water
Nonflammable but greatly accelerates combustion

6. Characteristics of Medical Gases (cont.)
Oxygen production
Fractional distillation
Produces most large quantities of O2
Atmospheric air is filtered to remove pollutants, water, & CO2
Purified air is liquefied by compression & cooled by rapid expansion (Joule-Thompson effect)
Resulting mixture is heated slowly to allow nitrogen to boil off, leaving just O2

7. Characteristics of Medical Gases (cont.)
Oxygen production (cont.)
Physical separation
Molecular sieves absorb nitrogen, trace gases, & water vapor from air
Oxygen concentrators pull ambient air through semipermeable plastic membrane

8. Characteristics of Medical Gases (cont.)
Air
Colorless, odorless, naturally occurring gas mixture
Contains 20.95% O2, 78.1% nitrogen, & ~1% trace gases (e.g., Argon)
Has density of 1.29 g/L.
Medical-grade air produced by filtering & compressing atmospheric air

9. Air

10. Characteristics of Medical Gases (cont.)
Carbon dioxide (CO2)
Colorless & odorless gas
Does not support combustion
Usually is produced by heating limestone in contact with water
Common uses for CO2 mixtures
Calibration of blood gas analyzers
Diagnostic purposes in clinical laboratory

11. Characteristics of Medical Gases (cont.)
Carbon dioxide (CO2) (cont.)
Mixtures of O2 & 5-10% CO2 have therapeutic purposes
AKA: “carbogen”
Management of singultus (hiccoughs)
Prevent complete washout of CO2 during cardiopulmonary bypass
Regulate pulmonary vascular pressures in some congenital heart disorders

12. management of singultus
Therapeutic purposes of carbogen (O2/CO2) include all of the following, except:
management of singultus
regulate pulmonary vascular pressures in congenital heart disorders
maintain patient’s PaCO2 during cardiopulmonary bypass
treat hypoxic respiratory failure in newborn infants
Answer: D

13. Characteristics of Medical Gases (cont.)
Helium (He)
Odorless, tasteless, nonflammable, & chemically & physiologically inert
Has density of g/L; much less than air
Commercially produced from natural gas through liquefaction to purity standards of at least 99%
Must always be mixed with at least 20% O2

14. Characteristics of Medical Gases (cont.)
Helium (He) (cont.)
Therapeutic use
Heliox (mixture of O2 & helium)
Manages severe cases of airway obstruction
Decreases work of breathing
Lower density
Makes gas flow more laminar

15. Characteristics of Medical Gases (cont.)
Nitric oxide (NO)
Colorless, nonflammable, toxic gas that supports combustion
Exposure to high concentrations alone can cause methemoglobinemia, which can cause tissue hypoxia
FDA approved for use in treatment of term & near-term infants with hypoxic respiratory failure

16. A newborn infant with persistent pulmonary hypertension has been placed on mechanical ventilation. What special therapeutic gas would you recommend to improve the neonate’s condition?
heliox
nitrous oxide
carbogen
nitric oxide
Answer: D

17. Characteristics of Medical Gases (cont.)
Nitrous oxide (N2O)
Colorless gas with slightly sweet odor & taste
Clinically used as anesthetic agent
Must always be mixed with oxygen
Produced by thermal decomposition of ammonium nitrate
Risks
Long-term exposure can lead to neuropathy issues
Fetal disorders
Spontaneous abortion

18. Storage of Medical Gases
Gas cylinders
Used to store & ship compressed or liquid medical gases
Design, manufacture, transport, &use of these cylinders are controlled by industrial standards & federal regulations
Made of seamless steel
Classified by U.S. Department of Transportation (DOT)
DOT type 3A cylinders are made from carbon steel
DOT type 3AA cylinders are made from steel alloy tempered for higher strength

19. Gas Cylinders Markings & identification
Color coded & marked with metal stamping on shoulder
Stamping indicates size, normal filling pressure, serial number, ownership, & method of manufacturer
Safety tests are conducted every 5 or 10 years
Cylinders are pressurized to five thirds of their service pressure
Cylinder leakage, expansion, & wall stress are measured
Results of pressure testing are stamped on tank

20. Gas Cylinders (cont.)

21. Gas Cylinders (cont.)

22. Gas Cylinders (cont.)

23. Gas Cylinders (cont.)

24. Gas Cylinders (cont.) Cylinder safety relief valves
Designed to vent gas to atmosphere if tank is heated
Prevents tank pressure from becoming too high
Basic designs
Frangible metal disk ruptures at specific pressure
Fusible plug melts at specific temperature
Spring loaded valve opens & vents gas at set high pressure

25. Gas Cylinders (cont.) Filling (charging) cylinders Compressed gases
Normally filled to its service pressure (pressure stamped on shoulder) at 70º F
Approved gas cylinders can be filled to 10% in excess of service pressure

26. Gas Cylinders (cont.) Filling (charging) cylinders Liquefied gases
Include CO2 & N2O
Cylinders filled according to specified filling density
Filling density is ratio between weight of liquid gas put into cylinder and weight of water cylinder could contain if full

27. Gas Cylinders (cont.) Measuring cylinder contents Gas-filled cylinders
Volume of gas in cylinder is directly proportional to its pressure
Liquid gas cylinders
Pressure does not relate to amount of liquid remaining
Only weight of cylinder indicates amount of gas inside

28. Gas Cylinders (cont.)

29. Gas Cylinders (cont.) Estimating duration of cylinder gas flow
Factors affecting duration of flow
Gas flow
Cylinder size
Cylinder pressure at start of therapy
Formulas:
Cylinder factor (L/psig) = Cubic feet (full cylinder) x 28.3 / Pressure (full cylinder) in psig
Duration of flow = Content / Flow
Duration of flow (min) = Pressure (psig) x Cylinder factor / Flow (L/min)

30. Gas Cylinders (cont.)
Estimating duration of liquid oxygen cylinder gas flow
Weight of gas must be known to determine volume of gas in liquid-filled cylinder
1L of liquid O2 weighs 2.5 lb & produces 860 L of O2 in its gaseous state
Amount of gas = Liquid O2 weight (lb)  860/2.5 lb/L
Duration of gas (min) = Amount of gas in container (L) / Flow (L/min)

31. What is the duration of flow for an E-cylinder with 1500 psig that is running at 5 L/min?
15.7 hours
0.8 hours
1.4 hours
0.84 hours
Answer: C

32. Gas Cylinder Safety Cylinder storage Store in racks or chain to wall
Do not store combustible material in vicinity of cylinders
Store away from sources of heat
Store flammable gases separately from gases that support combustion

33. Gas Cylinder Safety Cylinder storage (cont.)
Keep cylinder cap in place if cylinder is not in use
Post “NO SMOKING” signs near storage units
Store liquid O2 containers in cool, well-ventilated area

34. Gas Cylinder Safety (cont.)
Cylinder use
Secure cylinders at patient’s bedside
Do not use flammable materials (e.g., oil) on regulators, cylinders, fittings, or valves
“Crack” or open cylinder valve slightly to remove dust before attaching regulator
Post “NO SMOKING” signs when O2 is used

35. Bulk Oxygen Used to meet large O2 needs of health care facilities
Systems hold at least 20,000 cubic feet of gas
O2 may be stored in gas or liquid form

36. Bulk Oxygen (cont.) Advantages over portable cylinders
Far less expensive over long term
Less prone to interruption
Eliminate inconvenience & hazard of transporting & storing large number of cylinders
Eliminate need for separate pressure-reducing valves at each outlet
Safer since they operate at low pressures

37. Bulk Oxygen-Gas Supply Systems
3 types
Alternating supply system or cylinder manifold system
Consists of large (normally H or K size) cylinders of compressed O2 banked together in series
When pressure in primary bank decreases to set level, control valve automatically switches over to reserve bank

38. Bulk Oxygen-Gas Supply Systems (cont.)

39. Bulk Oxygen-Gas Supply Systems (cont.)
3 Types (cont.)
Cylinder supply system with reserve supply
Consists of primary supply, secondary supply, & reserve supply
When primary gas supply is depleted by demand, this supply system automatically switches to secondary supply
Bulk gas system with reserve
Most commonly used in large health facilities for economical, safety, & convenience reasons
Small volume of liquid O2 provides very large amount of gaseous O2 & minimizes space requirements

40. Bulk Oxygen-Gas Supply Systems (cont.)

41. Bulk Oxygen-Gas Supply Systems (cont.)
Safety precautions
Failure of bulk O2 supply can be life threatening to patient receiving O2 or gas-powered ventilatory support
Facilities should have second, smaller liquid stand tank or cylinder gas manifold as backup
Staff must be prepared to identify affected patients & move appropriate backup equipment to bedside (portable cylinders, bag-mask resuscitators, etc.)

42. Distribution & Regulation
Primary function of distribution & regulation system is to deliver O2/air to bedside at useable pressure
Central piping system
Used to deliver compressed gas to all areas throughout hospital
Gas pressure reduced to standard working pressure of 50-psi at bulk storage location
Main alarm warns of pressure drops or interruptions in flow from source
Zone valves located throughout system
Closed for system maintenance or in case of fire

43. Central Piping System

44. Zone Valves

45. Safety Indexed Connector Systems
3 systems used to ensure correct gas source
American Standard Safety System (ASSS)
For large cylinders & their attachments
Prevents accidental misconnections
Diameter-Index Safety System (DISS)
For low-pressure gas connectors
Found at outlets of pressure-reducing valves , outlets of central piping systems, & inlets of blenders, flowmeters, vents

46. American Standard Safety System

47. Safety Indexed Connector Systems (cont.)
3 systems are used (cont.)
Pin-Index Safety System (PISS)
For small cylinders (up to & including size E) & their attachments
Cylinders have yoke type connection
Exact positions of pins & pinholes vary for each gas
2 - 5 for oxygen
1 - 5 for air

48. You are called to prepare an E-cylinder of oxygen for a patient
You are called to prepare an E-cylinder of oxygen for a patient. Which pinhole locations on a regulator should be used?
1 and 5
2 and 5
2 and 6
1 and 6
Answer: B

49. Pin-Index Safety System

50. Diameter-Index Safety System

51. Regulating Gas Pressure & Flow
Reducing valve is used to reduce gas pressure to useable level
Flowmeter is used to control flow to patient
Regulator is used to control both pressure & flow

52. Reducing Valve

53. Low-Pressure Gas Flowmeters
Flowmeters allow rate of gas flow to patient to be set & controlled
Three categories of flowmeters are used:
Flow restrictor
Bourdon gauge
Thorpe tube

54. Low-Pressure Gas Flowmeters (cont.)
Flow restrictor
Simplest & least expensive flowmeter device
Consists of fixed orifice calibrated to deliver specific flow at constant pressure
Operation is based on principle of flow resistance

55. Low-Pressure Gas Flowmeters (cont.)
Flow Restrictor (cont.)
Gas flow through tube can be quantified
R = P1 – P2 / V rearranged to V = P1 – P2 / R
V = volumetric flow per unit time, P1 is pressure at upstream point, P2 is pressure at downstream point, & R is total resistance to gas flow

56. Flow Restrictor

57. Low-Pressure Gas Flowmeters (cont.)
Bourdon Gauge
Always used in combination with adjustable pressure-reducing valve
Uses fixed orifice but operates under variable pressures
Not gravity dependent; ideal for patient transport
Not accurate when pressure distal to orifice changes

58. Bourdon Gauge

59. Bourdon Gauge

60. Low-Pressure Gas Flowmeters (cont.)
Integrated oxygen cylinders
Includes Grab ‘n Go System
Eliminates need for separate oxygen tanks, Bourdon gauge regulators, & oxygen keys/wrenches
Flow is selected & oxygen tubing to system connection can simply be connected to patient

61. Grab ‘n Go System

62. Low-Pressure Gas Flowmeters (cont.)
Thorpe Tube
Functions as flow variable-orifice, constant pressure flowmeter device
Increasing size of orifice increase gas flow
Always attached to 50-psig source
Used to measure true flow

63. Thorpe Tube

64. Low-Pressure Gas Flowmeters (cont.)
Thorpe Tube Types
Pressure compensated
Prevents changes in downstream resistance, or back pressure, from affecting meter accuracy
Calibrated at 50-psig instead of at atmospheric pressure
Flow control needle valve placed after (distal to) flow tube
Gravity dependent; not ideal for patient transport

65. Low-Pressure Gas Flowmeters (cont.)
Thorpe Tube Types (cont.)
Uncompensated
Calibrated in liters per minute at atmospheric pressure (without restriction)
Gas from 50-psig source flows into meter at rate controlled by needle valve located before flow tube

66. Thorpe Tube

67. backpressure-compensated Thorpe non-backpressure-compensated Thorpe
A patient on nasal cannula needs to be transported on a stretcher. The O2 cylinder used is laid flat under the stretcher. Which flowmeter should be recommended?
backpressure-compensated Thorpe
non-backpressure-compensated Thorpe
flow restrictor
Bourdon
Answer: D

68. Role of Respiratory Therapists
Patient assessment
Patient interview
Obtain vital signs
Determine patient’s pathophysiological state by analyzing available information
Recommend appropriate treatment
Proper medical gas used
Regulators, flowmeters, & additional equipment

69. Role of Respiratory Therapists (cont.)
Monitor outcomes
Observe adverse reactions
Modify any necessary oxygen flow or treatment
Troubleshoot equipment
Terminate treatment when appropriate