Humidification
- Humidification is the method by which humidified air can be introduced into the respiratory system.
- Heat and moisture exchange is one of the most important functions of the respiratory system.
- The rich vascular system of numerous thin-walled veins of connective tissue in the nose is responsible for warming the inspired air to increase its humidity-carrying capacity.
Isothermic Saturation Boundary:
- Usually located 5 cm below the cornea, where the temperature is 37 °C, and the relative humidity is 100%.
Effects of Humidification:
- Maintain viscosity of airway secretion.
- Protection of the respiratory tract through the mucous line of defense.
- Adequate ciliary function.
- Prevention of dehydration and immobilization of cilia.
- Facilitates easy mucociliary clearance.
Indications:
- Any interference with the normal function of the upper respiratory tract.
- Supplemental oxygen administration.
- Dry gas delivery.
- High flow oxygen exceeding 4 liters per minute.
- Bypassing the upper airway.
- Post-extubation care.
- Irritated airway conditions.
- Thick consistency of mucus.
Principle of Humidifier Function:
- Temperature: As the temperature of the gas increases, its ability to hold water vapor increases, and vice versa.
- Surface Area: Greater surface area contact between water and gas provides more opportunities for evaporation to occur.
- Time of Contact: Prolonged contact between gas and water increases the opportunity for evaporation.
- Thermal Mass: A higher mass of water or core element in a humidifier enhances its capacity to transfer or hold heat.
Delivery Method:
- For patients not intubated, options include:
- Face mask.
- Mouthpiece, which the patient holds.
- This method is frequently used with a nebulizer as a means of providing short-term humidification before chest clearance.
Methods of Humidification
- Heat and Moisture Exchange (HME)
- Lightweight disposable device
- Used with mechanical ventilation or breathing spontaneously
- Collects and conserves the patient's expired moisture to heat with a filter for bacteria and viruses, becoming a Heat and Moisture Exchanging filter (HMEF)
- Bubble Humidifiers
- The gas passes through a tube to the bottom of the water reservoir
- Gas bubbles rise in the reservoir
- Provides humidity for oxygen therapy
- Passover Humidifier
- Directs gas over liquid or over a surface saturated by liquid
- Types:
- Simple reservoir model
- Wick units
- Membrane device
- Simple reservoir: Gas flows over the surface of a volume of water, usually heated, to provide humidity to mechanically ventilated patients
- Hazards:
- Inhalation of cold mist on water may cause bronchoconstriction in patients with hyperreactive airways.
- Water reservoirs are a good culture medium for bacteria, increasing the risk of infection
Nebulization
- Nebulization is the method of administering drugs by inhalation
- Liquid nebulization is a common method of medical aerosol generation
- A nebulizer converts liquid into aerosol droplets (fine mist) suitable for inhalation
- Nebulizers use oxygen, compressed air, or ultrasonic power to break up medication solutions and deliver therapeutic doses of aerosol particles directly to the lungs
Indications
- Delivery of bronchodilator drugs (e.g., asthma)
- Administration of antibiotics and antifungal agents (e.g., cystic fibrosis)
- To aid expectoration (e.g., bronchial secretions)
- Local analgesia (e.g., alveolar carcinoma)
Contraindications
- Patients with unstable and increased blood pressure
- Individuals with cardiac irritability (may result in dysrhythmias)
- Persons with tachycardia
- Unconscious patients (therapeutic effect may be significantly low)
Disadvantages and Precautions
- Drug availability varies with different types of nebulizers
- Cool-inspired air carries the risk of bronchospasm
- Bacterial contamination is a concern
- Patient adherence may be hindered
- Patients may become over-dependent
Ideal Nebulizer
- Minimum residual volume (10.5ml)
- Aerosol is delivered only during inhalation
- No waste aerosol should be released into the environment
- Small and portable
- Aerosol delivered with a droplet size distribution suitable for pulmonary deposition
- Rapid treatment time, quiet and unobtrusive in use
- Monitor patient compliance
Particle Size
- Mass median aerodynamic diameter
- < 1 µm: Reaches up to the alveoli
- 0.5-5 µm: Beyond the 10th generation of bronchi (respirable particles)
