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Overview of Medical Gases

• Medical gases are crucial in healthcare, particularly in oxygen therapy and anesthetics.

• This chapter focuses on the storage and delivery systems for medical gases, emphasizing practical understanding.

Classification of Medical Gases

• Laboratory Gases: Used for calibrating equipment and diagnostic testing.

  • Example: Used in pulmonary function tests to check machine accuracy.

• Therapeutic Gases: Aimed at relieving symptoms and improving patient oxygenation, especially for hypoxemia.

• Anesthetic Gases: Provided with oxygen for anesthesia during surgeries.

Characteristics of Oxygen

• Properties: Colorless, odorless, tasteless, transparent.

• Density at STP: 1.429 grams/liter (slightly heavier than air).

• Solubility: Minimal in water with only 3.3 mL of oxygen dissolving in 100 mL at room temperature (not crucial to memorize).

• Combustion: Non-flammable but accelerates combustion; must keep flammable materials away.

Production of Medical Oxygen

• Chemical Methods: Produce small volumes; examples include electrolysis of water.

• Fractional Distillation: Most common method; filters and liquefies atmospheric air, separates oxygen (21% in air) from nitrogen.

• Physical Separation: Involves methods like molecular sieves and oxygen concentrators, the latter extracting oxygen from ambient air.

Medical Air

• Comprised mainly of atmospheric air: approximately 21% oxygen and 78% nitrogen; has been filtered and compressed to remove pollutants.

• Commonly used in devices like nebulizers that deliver filtered air for therapeutic use.

Use of Compressed Medical Gases

• Carbon Dioxide (CO2): Used in calibration and laboratory tests, colorless and non-flammable but supports combustion; FDA purity standard is 99%.

• Helium: Therapeutic for airway constriction due to its low density; needs to be mixed with oxygen for safety.

• Nitric Oxide: Colorless, toxic gas used primarily as a pulmonary vasodilator, particularly for infants with hypoxic respiratory failure.

• Nitrous Oxide: Commonly known as laughing gas; used as an anesthetic agent, requiring a mixture with oxygen at all times.

Storage and Safety of Medical Gases

• Gases are stored in gas cylinders made of seamless steel, regulated by the Department of Transportation.

• Safety features include pressure relief valves to avoid explosive incidents from overheating or over-pressurization.

• Charging (Filling) Cylinders: Involves specific techniques; most often done by dedicated services, especially in hospital settings.

Estimating Cylinder Duration

• The gas duration can be estimated using the formula:Duration(mins) = (Pressure (PSI) * Cylinder Factor) / Flow Rate (L/min)

• For example, an E cylinder at 1,500 PSI at 5 L/min lasts 84 minutes.

Humidity and Aerosol Therapy

• Upper airway's role is to heat and humidify inspired air; loss of humidity occurs with artificial airways like ET tubes or trach.

• Humidity Deficit: Infection and complications can occur due to inadequate humidity intake; supplemental humidity is required for patients bypassing the upper airway.

Types of Humidifiers

• Active Humidifiers: Include bubble humidifiers, passover humidifiers, nebulizers, and vaporizers which add water and/or heat.

• Passive Humidifiers: Heat Moisture Exchangers (HMEs) recycle exhaled moisture for added humidity when breathing in.

Using Humidifiers

• Temperature and Flow Rate: Higher temperature generates more humidity; however, high flow rates can reduce contact time leading to less humidity absorption.

• Clinical Uses: To manage bronchospasm, intubation recovery, upper airway edema, and to induce sputum sample production.

Bland Aerosol Therapy

• Involves liquid particles suspended in gas; can include sterile saline for hydration or medicated solutions.

• Used to manage airway edema, promote secretions, or assist in working with artificial airways.

• Common devices include jet nebulizers or larger volume nebulizers, which adjust for adequate FiO2 levels while providing humidity.

Safety and Considerations

• Attention to potential complications like infections, overhydration, and airway irritation from excessive humidity or incorrect use of nebulizers.

• Monitor settings and patient responses closely during aerosol therapy.

Summary

• Understanding the properties, production, storage, and delivery of medical gases is critical in respiratory care.

• Mastery of these concepts ensures effective treatment and promotes patient safety in diverse clinical scenarios.