Reference — Transport Respiratory Care
Gas Laws for Patient Transport
The gas laws that matter in transit, each with its statement, formula, and the bedside-in-the-sky implication — from Boyle expanding a pneumothorax to Dalton thinning inspired oxygen at altitude.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Several gas laws describe how gases behave as pressure and temperature change during transport. Boyle’s and Dalton’s laws are the most clinically important in flight; the others round out the picture. Read each implication as something you act on before, not during, transport.
Gas Laws at a Glance
| Law | Statement & Formula | Transport Implication |
|---|---|---|
| Boyle’s law | At constant temperature, pressure × volume is constant (P₁V₁ = P₂V₂) | As barometric pressure falls at altitude, trapped gas expands — pneumothorax, ETT cuff, bowel gas, ears/sinuses. Decompress closed spaces before flight. |
| Charles’s law | At constant pressure, volume is proportional to absolute temperature (V₁/T₁ = V₂/T₂) | Temperature changes alter gas volume; relevant to cold cabins and gas delivery. |
| Gay-Lussac’s law | At constant volume, pressure is proportional to absolute temperature (P₁/T₁ = P₂/T₂) | A cooled fixed-volume cylinder reads a lower pressure; temperature affects cylinder gauge readings. |
| Dalton’s law | Total pressure equals the sum of partial pressures (Pₜₒₜₐₗ = ΣPᴳₐₛ) | As barometric pressure falls, the partial pressure of inspired O₂ (PiO₂) falls at constant FiO₂ — the cause of altitude hypoxia. Raise FiO₂ to compensate. |
| Henry’s law | The amount of gas dissolved in a liquid is proportional to its partial pressure | Dissolved-gas behavior; underlies decompression/bubble concepts with large pressure changes. |
| Graham’s law | The diffusion rate of a gas is inversely proportional to the square root of its molecular weight | CO₂ diffuses faster than O₂ across the alveolar membrane; conceptual basis for gas exchange. |
Clinical Notes
- Boyle’s law is the single most actionable law in flight. Expanding trapped gas is what makes an untreated pneumothorax dangerous and an air-filled ETT cuff a hazard at altitude.
- Dalton’s law explains altitude hypoxia. A patient who was adequately oxygenated at sea level may desaturate at cabin altitude despite an unchanged FiO₂ — because the partial pressure of inspired O₂ (PiO₂) falls as barometric pressure drops.
- These laws describe the same physical reality from different angles. Pressure, volume, and temperature are linked — understanding each law individually makes it easier to predict combined effects during a long-distance or high-altitude transport.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Physics of gas behavior.
- Commission on Accreditation of Medical Transport Systems. Accreditation Standards of the Commission on Accreditation of Medical Transport Systems. 11th ed. CAMTS; 2018.