Chapter_041

Learning Objectives

• Explain production methods, clinical applications, and storage formats for medical gases & gas mixtures.
• Perform run-time calculations for compressed and liquid O$_2$ cylinders.
• Apply proper procedures for storing, transporting, and using cylinders.
• Differentiate bulk supply and central piping systems; outline emergency actions if bulk O$_2$ fails.
• Match pressure-regulating / flow-control devices to clinical situations; assemble, test, and troubleshoot them.
• Identify and apply all relevant connector safety systems (ASSS, PISS, DISS, quick-connect).

Classification & General Uses of Medical Gases

• Laboratory gases ⇒ calibration / diagnostics.
• Therapeutic gases ⇒ relieve symptoms, improve oxygenation in hypoxemia.
• Anesthetic gases ⇒ combined with O$_2$ during surgery.

Physical & Chemical Characteristics of Individual Gases

• O$_2$

• Colorless, odorless, tasteless, transparent.
• STPD density = 1.429\;\text{g·L}^{-1} (heavier than air).
• Poor water solubility (3.3 mL per 100 mL).
• Non-flammable yet accelerates combustion; burn rate ↑ with ↑ partial pressure or ↑ concentration.
  • Air
• 20.95 % O$2$, 78.1 % N$2$, ≈1 % trace gases; density = 1.29\;\text{g·L}^{-1}.
• Medical-grade → filtered & compressed.
  • CO$_2$
• Colorless, odorless, specific gravity = 1.52 (≈1.5× air).
• Non-combustible; produced by heating limestone + H$_2$O; FDA purity ≥99 %.
• Uses: blood-gas analyzer calibration, lab diagnostics.
  • Helium
• Inert, density = 0.1785\;\text{g·L}^{-1} (≈1/7 of air).
• Obtained from natural-gas liquefaction → purity ≥99 %.
• Must contain ≥20 % O$_2$; Heliox (e.g.
  80 : 20) ↓ airway resistance, promotes laminar flow, ↓ work of breathing in severe obstruction.
  • Nitric Oxide (NO)
• Colorless, toxic, supports combustion.
• High doses → methemoglobinemia → tissue hypoxia.
• FDA-approved for term / near-term neonates with hypoxic respiratory failure.
  • Nitrous Oxide (N$_2$O)
• Colorless, slightly sweet odor/taste; anesthetic.
• Always delivered with O$_2$.
• Made by thermal decomposition of ammonium nitrate.
• Chronic exposure risks: neuropathy, fetal disorders, spontaneous abortion.

Oxygen Production Methods

• Chemical (small-scale)

• Electrolysis of H$_2$O.
• Thermal decomposition of NaClO$_3$.
  • Fractional Distillation (large-scale, cheapest)
• Filter ambient air (remove pollutants, H$2$O, CO$2$).
• Compress & rapidly expand (Joule-Thomson) → liquefaction.
• Slow warming → N$2$ boils off first, leaving liquid O$2$.
  • Physical Separation (small-scale)
• Molecular sieve concentrators (zeolite removes N$2$, H$2$O, trace gases).
• Membrane concentrators (semipermeable plastic; N$2$ diffuses faster than O$2$).

Storage of Medical Gases – Cylinders

• Construction & Regulation

• Seamless steel; DOT 3A (carbon steel) or 3AA (heat-treated alloy).
• Color coding + shoulder stamp → size, service pressure, serial #, manufacturer, owner.
• Hydrostatic test q5–10 yr @ \frac{5}{3} service pressure; measures leakage, expansion, wall stress (results re-stamped).
  • Relief Devices
• Frangible disk (ruptures at set pressure).
• Fusible plug (melts at specific temperature).
• Spring-loaded valve (opens @ preset pressure).
  • Filling Rules
• Compressed gases → filled to stamped service pressure @ 70 °F; may overfill by 10 % if DOT-approved.
• Liquefied gases (CO$2$, N$