Humidity and Aerosol Therapy in Medical Practice

Humidity

Water that exists in the form of individual molecules in the vaporous or gaseous state.

Size of Water Molecules

Molecules of water are about 0.001 µm.

Medical Aerosols

Medical aerosols can range from 0.2 to 50 µm.

Atomizers

Devices used to generate medical aerosols.

Nebulizers

Devices used to generate medical aerosols.

Inhalers

Devices used to generate medical aerosols.

Condensation

Occurs when vapors cool and collects in the lowest point of the circuit.

Relative Humidity (RH)

As temperature increases, the amount of water a gas can hold increases, decreasing its Relative humidity (RH).

Humidity Management Methods

Condensation is managed by placing water traps at the lowest point in the circuit or using a heated wire circuit.

Heat Moisture Exchange

A primary function of the respiratory tract that adds heat and humidity during inspiration and retains it during exhalation.

Humidity Therapy

Involves adding water vapor to inspired gas.

Isothermic Saturation Boundary

Point in airway where inspired gas is saturated with humidity at body temperature, usually occurring 5 cm below carina.

Indications for Humidification Therapy

Primary: Humidifying dry medical gases; Overcoming humidity deficit created when upper airway is bypassed.

Secondary Indications for Humidification

Treating bronchospasm caused by cold air.

Inspissated Secretions

Thick pulmonary secretions that occur as the production of mucus increases.

Humidity Injury Threshold

When the RH of inspired gas is greater than 60% of Body temperature and pressure saturated (BTPS) conditions, no injury is believed to occur in normal lungs.

Contraindications for Humidity Therapy

Humidity devices may be contraindicated in patients with upper airway hyperresponsiveness or at risk for bronchoconstriction.

Humidifiers

Devices that add molecular water (vapor) to gas.

Factors Affecting Humidifier Performance

Time of contact, temperature, surface area of contact, and thermal mass.

Contact Time

The longer the time of contact, the more time for evaporation to occur.

Temperature Effect on Humidity

As temperature increases, capacity (potential humidity) will increase.

Surface Area Effect on Humidity

The greater the surface area, the more potential for evaporation.

Thermal Mass

The more water in the humidifier, the more potential for transfer of heat.

Types of Humidifiers

Humidifiers are either active (actively adding heat or water) or passive (recycling exhaled heat and humidity).

Active Humidifiers

Include bubble humidifiers, passover humidifiers, nebulizers of bland aerosols, and vaporizers.

Passive Humidifiers

Refer to typical heat and moisture exchangers (HMEs).

Bubble Humidifiers

Break underwater gas stream into small bubbles to increase surface area for gas/water interaction.

Unheated Bubble Humidifier Output

Can provide an absolute humidity level of 10 to 20 mg/L.

High-Flow Humidifiers

Used with mechanical ventilation and designed to accommodate flow rates of gas delivered up to 100 L/min.

Passover Humidifiers

Directs gas over water surface and includes simple reservoir type, wick type, and membrane type.

Heated Humidifiers

Devices that increase humidity for respiratory patients.

Absolute Humidity

Amount of water vapor in a gas.

Mechanical Ventilation

Assisted breathing using machines for patients.

Airway Burns

Injuries caused by heated inhaled gases.

Large Bore Heated Tubing

Reduces condensation and obstruction in humidifiers.

Optimum Humidity

Ideal humidity levels for airway conditions.

AARC Guidelines

Recommendations for respiratory care practices.

Humidity Level for Intubated Patients

At least 30 mg/L of humidity required.

High-Flow Heated Humidifiers

Used with high-flow systems for ventilation.

Water Reservoir

Large container for humidifier water supply.

Gravity Feed System

Uses gravity to maintain water levels automatically.

Manual System

Requires manual refilling of humidifier water.

Wick Humidifier

Gas passes through water-saturated material.

Heat-Moisture Exchangers (HMEs)

Passive devices that recycle exhaled humidity.

Simple Condenser Humidifier

Traps heat and humidity from exhaled gas.

Hygroscopic Condenser Humidifier

Uses hygroscopic materials to enhance humidity.

Hydrophobic Condenser Humidifier

Water-repellent element that retains humidity.

Flotation Valve

Maintains fluid volume in humidifier reservoir.

Vapotherm 2000i

Device for heating and humidifying oxygen.

Condensation Prevention

HMEs with filters reduce infection risks.

Maximum Absolute Humidity

Upper limit of humidity in gas delivery.

Thin-Film Boiler

High-surface area device for humidification.

Heating Elements

Components that require energy to heat water.

Inspiratory Line

Pathway for gas delivery to patients.

Cross-Contamination

Unwanted transfer of pathogens between systems.

Molecular Humidity

Humidity that decreases infection risk.

Heat Moisture Exchanger (HME)

Device that conserves heat and moisture in gas.

Mechanical Dead Space

Volume added by HMEs, 30 to 90 mL.

Uncuffed Endotracheal Tubes (ETTs)

ETTs allowing gas leakage, reducing HME efficiency.

Heated Humidity

Humidity provided at temperatures below 35°C causes obstruction.

Active HMEs

Devices adding heat or humidity to inspired gas.

Relative Humidity

Amount of moisture in gas, 100% at BTPS.

Minute Volume

Total gas volume breathed per minute, 4 to 20 L.

Humid-Heat System

Absorbs expired moisture, releases into inspired gas.

HME Booster

T-piece with heated element for specific patient volumes.

Contraindications for HMEs

Conditions where HMEs should not be used.

Tidal Volume

Volume of air per breath, >700 mL contraindicates HMEs.

Cross Contamination

Risk of infection from humidification systems.

Bland Aerosol Therapy

Therapy using liquid particles in gas.

Indications for Cool Bland Aerosol

Conditions like laryngotracheobronchitis requiring humidification.

Large-Volume Nebulizers

Devices generating bland aerosol using Bernoulli principle.

Air:Oxygen Ratios

Proportions of air to oxygen for different FiO2 levels.

Calculation for Air:Oxygen Ratios

Liters air = (100-O2%); Liters O2 = (%O2-21).

Variable Air-Entrainment Port

Allows air mixing to adjust flow rates and FiO2.

Heated Nebulizers

Produce 35 to 55 mg H2O/L due to vapor capacity.

Self-Filling Humidifiers

Reduce cross contamination in humidification systems.

Water Traps

Placed in circuits to minimize condensation risks.

Temperature Probes

Ensure accurate temperature readings in humidification systems.

Wick Humidifiers

Lower infection risk by preventing bacterial aerosols.

Aerosol Face Mask

Device for delivering aerosol therapy to patients.

Postextubation Edema

Swelling after extubation requiring humidification support.

Large-Volume Jet Nebulizers

Generate liquid particles using high-velocity gas.

Babington Nebulizer

Uses glass sphere to produce high-density aerosol.

Spinning Disk Device

Centrifugal nebulizer for home aerosol delivery.

Ultrasonic Nebulizers

Use vibrations to create high-density aerosol.

Particle Size

Inversely proportional to transducer's signal frequency.

Aerosol Production Rate

Directly related to transducer's signal amplitude.

Sputum Induction

Diagnoses diseases using hypertonic saline aerosols.

Airway Appliances

Devices for delivering bland aerosol therapy.

Aerosol Mask

Short-term therapy for patients with intact airways.

Face Tent

Used for patients intolerant to masks.

Tracheostomy Mask

Designed for patients with tracheostomy.

T-tube

Used for tracheostomy patients needing oxygen.

Mist Tents

Deliver aerosol therapy to infants and children.

Cross-contamination

Risk minimized by proper cleaning of equipment.

Environmental Concerns

Aerosol exposure can trigger asthma symptoms.

Inadequate Mist Production

Caused by flow issues or system leaks.

Overhydration Risk

Greatest in infants; requires careful monitoring.

Bronchospasm Monitoring

Risk increases with hypotonic aerosol solutions.

Negative Pressure Room

Prevents airborne infection spread; HEPA filters used.