med gas

• Medical gases and gas mixtures are produced through fractional distillation or physical separation
• Oxygen is colorless, odorless, transparent, and tasteless with a density of 1.429 g/L
• Oxygen greatly accelerates combustion but is nonflammable
• Oxygen production involves filtering atmospheric air to remove pollutants, water, and CO2, then liquefying and heating the purified air to separate nitrogen, leaving just O2
• Air is a colorless, odorless gas mixture containing 20.95% O2, 78.1% nitrogen, and trace gases
• Carbon dioxide is colorless, odorless, and does not support combustion
• Mixtures of O2 and 5-10% CO2 have therapeutic purposes, such as managing singultus and regulating pulmonary vascular pressures
• Helium is odorless, tasteless, and inert, with a density of 0.1785 g/L
• Heliox, a mixture of O2 and helium, is used to manage severe airway obstruction
• Nitric oxide is colorless, toxic, and supports combustion, used in treating hypoxic respiratory failure in infants
• Nitrous oxide is a colorless gas used as an anesthetic agent, produced by thermal decomposition of ammonium nitrate
• Gas cylinders are used to store and ship compressed or liquid medical gases, made of seamless steel
• Gas cylinders are marked with size, filling pressure, serial number, and undergo safety tests every 5 or 10 years
• Cylinder safety relief valves prevent tank pressure from becoming too high
• Gas-filled cylinders are filled to service pressure at 70º F, while liquefied gases are filled according to specified filling density
• Volume of gas in a cylinder is directly proportional to its pressure
• Duration of flow from a gas cylinder is affected by gas flow, cylinder size, and pressure at start of therapy
• Duration of flow from a liquid oxygen cylinder is calculated based on the weight of gas and flow rate
• For an E-cylinder with 1500 psig running at 5 L/min, the duration of flow is 0.8 hours
• Duration of flow for an E-cylinder with 1500 psig running at 5 L/min is 15.7 hours
• Gas Cylinder Safety:

  • Store cylinders in racks or chain to wall
  • Do not store combustible material near cylinders
  • Store away from sources of heat
  • Store flammable gases separately from gases that support combustion
• Gas Cylinder Safety (cont.):

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

  • Secure cylinders at patient's bedside
  • Do not use flammable materials 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
• 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
• Bulk Oxygen (cont.):

  • Advantages over portable cylinders:
  • Far less expensive over the 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 operation at low pressures
• Bulk Oxygen-Gas Supply Systems:

  • 3 types:
  • Alternating supply system or cylinder manifold system
  • Consists of large cylinders of compressed O2 banked together in series
  • Control valve automatically switches over to reserve bank when pressure in primary bank decreases to set level
• Bulk Oxygen-Gas Supply Systems (cont.):

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

  • Safety precautions:
  • Failure of bulk O2 supply can be life-threatening
  • Facilities should have a 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
• Distribution & Regulation:

  • Primary function is to deliver O2/air to bedside at usable pressure
  • Central piping system delivers compressed gas 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 for maintenance or in case of fire
• Safety Indexed Connector Systems:

  • 3 systems used to ensure correct gas source:
  • American Standard Safety System (ASSS) for large cylinders & their attachments
  • Diameter-Index Safety System (DISS) for low-pressure gas connectors
  • Pin-Index Safety System (PISS) for small cylinders (up to & including size E) & their attachments
• Regulating Gas Pressure & Flow:

  • Reducing valve used to reduce gas pressure to usable level
  • Flowmeter controls flow to patient
  • Regulator controls both pressure & flow
• Low-Pressure Gas Flowmeters:

  • Three categories used:
  • Flow restrictor
  • Bourdon gauge
  • Thorpe tube
• 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 based on principle of flow resistance
• 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
• 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
• Low-Pressure Gas Flowmeters (cont.):

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

  • Thorpe Tube Types:
  • Pressure compensated:
  • Prevents changes in downstream resistance from affecting meter accuracy
  • Calibrated at 50-psig instead of at atmospheric pressure
  • Flow control needle valve placed after flow tube
• Low-Pressure Gas Flowmeters (cont.):

  • Thorpe Tube Types (cont.):
  • Uncompensated:
  • Calibrated in liters per minute at atmospheric pressure
  • Gas from 50-psig source flows into meter at rate controlled by needle valve
• Role of Respiratory Therapists:

  • Patient assessment:
  • Obtain vital signs
  • Determine patient's pathophysiological state
  • Recommend appropriate treatment
  • Proper medical gas used
  • Monitor outcomes
  • Troubleshoot equipment
  • Terminate treatment when appropriate
• A patient on nasal cannula needs to be transported on a stretcher with the O2 cylinder laid flat under the stretcher. The recommended flowmeter is non-backpressure-compensated Thorpe