Introduction to Medicinal Gases
Medicinal Gases are gaseous preparations intended for use in diagnosis, anesthesia, and treatment during medical emergencies. These gases play a vital role in sustaining life, managing anesthesia, and aiding surgical procedures.
Although many gases occur naturally in the environment, industrial and environmental factors such as pollution and deforestation have necessitated the controlled production of pure medical-grade gases for healthcare and experimental use.
The most important therapeutic gases include Oxygen, Nitrous Oxide, Helium, and Carbon Dioxide. These are used in pre-operative, intra-operative, post-operative, and emergency medical conditions.
Oxygen (O2)
- Chemical Formula: O₂
- Molar Mass: 32 g/mol
Introduction
Oxygen is the most abundant element on Earth, forming about 46.6% of the Earth’s crust and 20.946% of the atmosphere by volume. It exists as a diatomic molecule (O₂) and is essential for respiration and metabolic functions in all aerobic organisms. In the body, oxygen is transported by hemoglobin and is critical for cellular energy production.
Preparation
- Laboratory Preparation: Decomposition of hydrogen peroxide (H₂O₂) using a catalyst such as manganese dioxide (MnO₂).
- Industrial Preparation: Obtained from air by removing CO₂ and water vapor, followed by liquefaction and fractional distillation to separate nitrogen and oxygen.
Assay
Assay is based on the absorption of oxygen by alkaline pyrogallol solution using a specific gas analysis apparatus designed for medicinal gases.
Properties
- Colorless, odorless, and tasteless gas.
- Diatomic in nature.
- Slightly soluble in water.
Uses
- Used in emergency therapy for hypoxia and respiratory distress.
- Supports life during surgery, anesthesia, and intensive care.
- Extensively used during the COVID-19 pandemic for patients with low oxygen saturation.
Storage Conditions
- Stored in high-pressure steel or aluminum alloy cylinders.
- Must be kept away from flammable materials due to its oxidizing nature.
- Store at controlled room temperature.
Carbon Dioxide (CO2)
- Chemical Formula: CO₂
- Molar Mass: 44.01 g/mol
Introduction
Carbon dioxide is a colorless, odorless gas with a faintly acidic taste. It is widely used in pharmaceutical and medical industries, particularly as a replacement solvent, in pH control, and in supercritical fluid chromatography.
In medicine, it is used as an insufflation gas during minimally invasive surgical procedures such as endoscopy, where it enlarges and stabilizes body cavities for better visibility and surgical precision.
Preparation
- Laboratory: By heating calcium carbonate (limestone) with dilute acid or by direct heating.
- Industrial: By heating limestone or as a byproduct from industrial fermentation processes.
Assay
Assay is based on absorption of carbon dioxide by 50% potassium hydroxide (KOH) solution. The volume of unabsorbed gas is measured to calculate the purity.
Properties
- Colorless and odorless gas with a slightly sour taste.
- Can exist as a solid form known as dry ice.
- Slightly soluble in water, forming carbonic acid (H₂CO₃).
Uses
- Used as a solvent substitute in pharmaceutical production.
- Acts as a pH controller in wastewater treatment.
- Used to carbonate beverages such as soft drinks.
- Applied as an insufflation gas during endoscopic surgeries.
Storage Conditions
- Store in cool, well-ventilated areas.
- Keep away from direct sunlight and heat sources.
- Temperature should not exceed 125°F (52°C).
Nitrous Oxide (N2O)
- Chemical Formula: N₂O
- Molar Mass: 44.03 g/mol
Introduction
Nitrous oxide, also known as laughing gas or dinitrogen oxide, is a colorless, sweet-smelling gas used as an anesthetic and analgesic. It induces a state of relaxation and mild euphoria when inhaled in small amounts and acts as a general anesthetic at higher concentrations.
Preparation
- By heating ammonium nitrate solution acidified with hydrochloric acid.
- By thermal decomposition of lead nitrate or ammonium nitrite.
Assay
Assayed by determining the volume of uncondensable gas in a gasometric setup using liquid nitrogen for condensation. The uncondensed gas must not exceed 5% v/v.
Properties
- Colorless gas with a sweet odor.
- Tasteless and non-irritating.
- Insoluble in water.
Uses
- Used as an inhalation anesthetic during surgical procedures.
- Acts as a pain reliever in dental surgeries and obstetrics.
- Serves as an oxidizing agent in certain chemical and pharmaceutical reactions.
Storage Conditions
- Store in a dry, cool, well-ventilated area.
- Keep away from direct sunlight and heat sources.
- Avoid storage near flammable materials.
Detailed Notes:
For PDF style full-color notes, open the complete study material below: