LZ

Storage and Delivery of Medical Gases

Learning Objectives

  • Describe production methods for medical gases & gas mixtures.
  • Discuss clinical applications for each medical gas / mixture.
  • Distinguish between gaseous vs. liquid storage methods.
  • Perform cylinder–duration calculations for both compressed and liquid O$_2$.
  • Explain proper procedures for storage, transport, & bedside use of cylinders.
  • Differentiate among hospital gas‐supply systems & outline emergency response to bulk O$_2$ failure.
  • Identify & apply the correct safety–index connector (ASSS, PISS, DISS, quick-connect).
  • Select & assemble devices that regulate pressure or control flow; check function & troubleshoot.

Classification & General Purpose of Medical Gases

  • Laboratory gases → calibration & diagnostics.
  • Therapeutic gases → symptom relief / improved oxygenation in hypoxemia.
  • Anesthetic gases → combined with O$_2$ to produce anesthesia in surgery.

Characteristics, Production, & Clinical Use of Individual Gases

Oxygen (O$_2$)

  • Physical properties
    • Colorless, odorless, tasteless, transparent.
    • Density at STPD: 1.429\;\text{g·L}^{-1} (slightly > air’s 1.29\;\text{g·L}^{-1}).
    • Poor water solubility → only 3.3\;\text{mL} dissolve per 100\;\text{mL} H$_2$O at 1 atm & room T°.
  • Supports (accelerates) combustion; non-flammable itself.
  • Production methods
    • Small-scale chemical: electrolysis of water; decomposition of \text{NaClO}_3.
    • Large-scale: fractional distillation (Joule–Thomson expansion; N$_2$ boiled off).
    • Physical separation:
    • Molecular sieves (N$_2$ adsorption).
    • Membrane concentrators (semipermeable plastic).

Air

  • Natural composition: 20.95\% O$2$, 78.1\% N$2$, \approx1\% trace gases.
  • Density at STPD: 1.29\;\text{g·L}^{-1}.
  • Medical grade produced by filtration + compression.

Carbon Dioxide (CO$_2$)

  • Colorless, odorless; specific gravity 1.52 (≈1.5× air).
  • Non-combustible.
  • Industrial production: heating limestone + H$_2$O.
  • FDA purity ≥ 99\%.
  • Uses: calibration of blood-gas analyzers; various lab diagnostics.

Helium (He)

  • Inert, non-flammable; density 0.1785\;\text{g·L}^{-1} (≈1/7 air).
  • Obtained from natural gas liquefaction, purity ≥ 99\%.
  • Must be blended with ≥20\% O$_2$.
  • Therapeutic mixture “Heliox” (He + O$_2$)
    • Manages severe airway obstruction.
    • ↓ Work of breathing via lower density → enhanced laminar flow.

Nitric Oxide (NO)

  • Colorless, non-flammable, toxic yet combustion-supporting.
  • High doses → methemoglobinemia → tissue hypoxia risk.
  • FDA-approved for term / near-term neonates with hypoxic respiratory failure.

Nitrous Oxide (N$_2$O)

  • Colorless, slightly sweet odor/taste.
  • Anesthetic agent; always combined with O$_2$.
  • Made via thermal decomposition of ammonium nitrate.
  • Chronic exposure hazards: neuropathy, fetal disorders, spontaneous abortion.

Storage of Medical Gases — Cylinders

Construction & Standards

  • Seamless steel per U.S. DOT.
    • Type 3A = carbon steel.
    • Type 3AA = tempered steel alloy (↑ strength).
  • Shoulder stamping: size, service pressure, serial #, owner, manufacturing method.
  • Safety hydrostatic test every 5 or 10 yrs → pressurize to \tfrac53 service pressure; record leakage, expansion, wall stress.

Safety Relief Devices

  • Vent to atmosphere if over-pressurized.
    • Frangible disk (ruptures at set P).
    • Fusible plug (melts at set T).
    • Spring-loaded valve (opens at set high P).

Filling (Charging)

  • Compressed gases (e.g., O$_2$, air)
    • Filled to stamped service pressure at 70^\circ\text{F}.
    • Certain cylinders may be filled to +10\% of service pressure.
  • Liquefied gases (CO$2$, N$2$O)
    • Filled per filling density:
      \text{Filling Density}=\tfrac{\text{Weight of liquid gas}}{\text{Weight of H}_2\text{O filling the same cylinder}}

Determining Contents

  • Gas-filled → volume ∝ pressure (ideal gas