Humidification is important to condition inspired gases and maintain normal physiology in the lower airways. The nose normally warms and humidifies air, but other devices are needed when the upper airways are bypassed. Active humidifiers like bubble and passover humidifiers add heat and water, while passive heat-and-moisture exchangers conserve moisture from expiration. Proper humidification prevents complications like infection and inflammation by keeping the isothermic saturation boundary below the carina. Different devices are suitable for various situations depending on factors like gas flow and ability to provide adequate humidity without risk.

1. TOPIC: HUMIDIFICATION
PHYSIOTHERAPY IN CARDIOPULMONARY CONDITIONS (BPT - 402)
CENTRE FOR PHYSIOTHERAPYAND REHABILITATION SCIENCES
JAMIA MILLIA ISLAMIA
SUBMITTED TO – DR. JAMAL ALI MOIZ
SUBMITTED BY – MAHEEN HASAN
BPT 4TH YEAR
ROLL NO. 17BPT014
DATE OF PRESENTATION – 22.01.2021 (Friday)
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2. INTRODUCTION
• Humidity is the presence of molecular water in a gas.
• Humidity Therapy is the addition of water vapour and sometimes heat to the medical gas that is delivered to a
patient.
Absolute humidity: The actual content or amount of water in a given volume of air. It is expressed in milligrams of
water per liter of gas (mg/L).
Relative humidity: The content of water vapour expressed as a percentage of the maximal capacity of water vapour
that can be held at the same temp.
Dew Point: The dew point is reached when the capacity becomes less than content, and water condenses and “rains
out” of the gas.
Isothermic Saturation Boundary (ISB): Point at which the inspired gas entering the respiratory tract is fully
saturated to 100% relative humidity at body temperature (37◦C). It is normally around the third generation of the
airways, about 5 cm below the carina. There are no fluctuations in temperature or relative humidity below the ISB,
whereas above the ISB, temperature and humidity increases on expiration and decreases on inspiration.
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3. PHYSIOLOGIC CONTROL OF HEAT AND MOISTURE EXCHANGE
• The conditioning of inspired air is the process by which a gas is warmed and moisturized during its passage
through the airways to reach the alveolar level under optimal conditions.
• The upper respiratory tract, particularly the nose, has the essential function of conditioning inspired gases for
optimal heat and moisture. The nasal mucosa has the greatest concentration of mucous glands in the airway and is
particularly vascular, providing a rich source of heat and water.
• It is crucial for the proper functioning of the lower airways and alveoli that inspired gases are fully saturated with
water vapour and warmed to body temperature upon reaching just below the carina.
• During inspiration, the induced turbulence in the flow of the inspired gas as it passes through the nose increases
the contact between the molecules of the inspired gas and nasal mucosa and results in efficient warming of the
inspired gas. The heat is transferred by turbulent convection over the turbinates and conchae.
• With the efficient warming of the inspired gas, water is then transferred and added to the inspired gas by
evaporation from the mucosa.
• Evaporation results in cooling and decreasing the water content of the tracheal and nasal mucosa.
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4. • During expiration, the tracheal and nasal mucosa cools the exhaled gas and recovers its heat and water content
through condensation.
• Below the isothermic saturation boundary, temperature and relative humidity remain constant.
• When the ISB is not achieved just below the carina, there will be a further distal downshift in the ISB.
Factors responsible for the downward shift of ISB are:
• when a person breathes through the mouth rather than the nose.
• when the person breathes cold, dry air.
• when the upper airway is bypassed.
• when the minute ventilation is higher than normal.
• With the distal shift of the ISB, additional surfaces from the lower airways will be required to provide humidity
and heat. This can negatively impact the epithelial integrity of these airways, make them susceptible to infection
and inflammation.
• Inadequate humidification can result in disruption of the mucociliary transport system and an increase in mucus
production with thickening of the pulmonary secretions, an increase in the airway irritability and ultimately
structural damage to the lung.
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5. GOALS
• The primary goal of humidification is to condition medical gases and maintain normal physiologic conditions in
the lower airways.
• With proper humidification, the ISB remains just below the carina with no downward shift toward the smaller
airways.
INDICATIONS
• Humidifying dry medical gases.
• Delivering adequate humidity for therapeutic purposes.
• Overcoming humidity deficit when upper airway is bypassed.
• Thinning dried or thick secretions.
• Managing hypothermia in intubated and mechanically ventilated patients.
• Treating bronchospasm caused by cold air.
• Providing adequate humidification in the presence of high gas flows during non invasive ventilation and high
flow nasal cannula oxygen therapy.
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6. Cool Humidity
• The delivery of cool humidified gas is used to treat upper airway inflammation resulting from croup,
epiglottitis, and post-extubation edema.
Hazards and Complications for Humidification Therapy
• Potential electrical shock (HH)
• Potential for burns to caregivers from hot metal (HH)
• Hypothermia (HME or inadequately set HH)
• Hyperthermia (HH)
• Thermal injury (HH)
• Underhydration and mucous impaction (HME or HH)
Physical Principles Governing Humidifier Function
• Temperature
• Surface area
• Contact time
• Thermal mass
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7. DEVICES USED FOR HUMIDIFICATION
• A humidifier is a device that adds molecular water to the inspired air.
TYPES OF HUMIDIFIERS
ACTIVE HUMIDIFIERS – Add water or heat or both to the inspired gas. These are classified according to the
method of contact between the water and gas.
• Bubble Humidifiers
• Passover Humidifiers
• Jet Nebulizers
Heated-water humidifiers are particularly useful for patients with bypassed upper airways and for those receiving
mechanical ventilatory support. Active humidifiers use electricity to heat the water or gas.
PASSIVE HUMIDIFIERS – Use the heat and moisture that is exhaled by the patient to humidify inspired gas.
• Heat-Moisture Exchangers (HMEs)
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8. BUBBLE HUMIDIFIER
• A bubble humidifier breaks or diffuses an underwater gas stream into small bubbles.
• Unheated bubble humidifiers are commonly used with nasal cannula, simple face mask and reservoir mask
where the flow rate of dry oxygen is less.
• Can provide absolute humidity levels between approx. 15 mg/L and 20 mg/L.
• Most efficient at flow 5 L/min. As gas flow increases, the reservoir cools and contact time is reduced that limits
the effectiveness at flow rates greater than 10 L/min.
DISADVANTAGES
• As gas flow increases, bubble humidifiers can produce aerosols. These water droplet suspensions can transmit
pathogenic bacteria from the humidifier reservoir to the patient.
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9. PASSOVER HUMIDIFIERS
• Passover humidifiers direct gas over a surface containing water.
TYPES
• Simple reservoir type: It directs gas over the surface of a volume of water (or fluid). The surface for gas-fluid
interface is limited.
• Wick type: A wick humidifier uses an absorbent material (paper or cloth) to increase the surface area for dry air
to interface with heated water. A wick is placed upright in a heated water reservoir. Capillary action draws water
up from the reservoir and keeps the wick saturated. As dry gas enters the chamber, it flows around the wick,
quickly picks up heat and moisture and leaves the chamber saturated with water vapor.
• Membrane type: A membrane-type humidifier separates the water from the gas stream by means of a
hydrophobic membrane. Water vapor molecules can easily pass through this membrane, but liquid water (and
pathogens) cannot.
ADVANTAGES
• Passover humidifiers can maintain saturation at high flow rates.
• They add little or no flow resistance to spontaneous breathing circuits.
• They do not generate any aerosols, and they pose a minimal risk for spreading infection.
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11. JET NEBULIZERS
• Uses a jet of compressed gas that passes through a restricted orifice, creating a low pressure area near the tip of
a narrow tube and drawing fluid from a reservoir, which is then shattered into droplets by the airstream.
• Jet nebulizers used as humidifiers can deliver between 26 and 35 mg/L of water when unheated. When heated,
they can deliver 33 to 55 mg/L of water.
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12. HEAT-MOIST EXCHANGER (HME)
• HMEs are devices that fit between the airway and the ventilator circuitry.
• Commonly referred to as artificial nose.
• As the exhaled gas pass through the HME, the water condenses on the inner surfaces and heat is retained. The retained
heat and moisture are then added to the next inspired breath.
• Since they conserve heat and water they are called conservers. Since they do not consume electricity
to work they are called passive humidifiers.
TYPES
Simple condenser humidifiers –
• Contain a condenser element with high thermal conductivity, usually consisting of metallic gauze, corrugated metal, or
parallel metal tubes.
• On inspiration, air cools the condenser to room temp. On exhalation, the saturated gas cools as it enters the condenser an
the water rains out while the temp. of condenser is increased. On next inspiration, cool dry air is warmed by the
condenser. It traps approx. 50% of exhaled moisture.
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13. Hygroscopic condenser humidifiers –
• Provide higher efficiency by using a condensing element of low thermal conductivity (e.g., paper, wool, or foam)
and impregnating this material with a hygroscopic salt (calcium or lithium chloride).
Hydrophobic condenser humidifiers –
• Use a water-repellent element with a large surface area and low thermal conductivity. During expiration the
condenser temp. rises to about 35◦. On inspiration, temp decreases to about 10◦. Efficiency is 70%.
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14. CONTRAINDICATIONS
• Presence of thick, copious and secretions containing blood.
• Presence of a large leak around an endotracheal tube.
• Body temp. of less than 32◦C.
• Minute ventilation of greater than 10 L/min.
HAZARDS
• Hypothermia.
• Underhydration.
• Impaction of pulmonary secretions.
• Increase in resistive work of breathing through the HME.
• Mucous plugging of the airways.
• Hypoventilation due to increased added dead space.
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15. REFERENCES
• Kacmarek, R. M., Stoller, J. K., Heuer, A. J. EGAN’s Fundamentals of Respiratory Care (11th ed.).
• Aaron, P., Solomen, S. Techniques in Cardiopulmonary Physiotherapy.
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16. THANK YOU
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