Aerosol and Humidity in Respiratory Care

Continuous Aerosol (Air-Entrainment)

Basic Equipment:

  • Air entrainment large volume nebulizer: Uses sterile water for inhalation; generates consistent aerosol particles and entrains room air to achieve specific oxygen concentrations. The sterile water prevents infection and provides moisture.

  • Two long pieces of large bore tubing: Essential for delivering the aerosolized gas from the nebulizer to the patient interface without excessive resistance or condensation buildup.

  • Drain bag: Collects condensate from the tubing, preventing re-entry into the nebulizer or patient airway, which could dilute medication or pose an infection risk.

  • Continuous aerosol oxygen delivery device/aerosol interface: Connects the tubing to the patient, ensuring effective delivery of the aerosol.

Aerosol Interfaces:

  • Tracheostomy tube collar (trach collar): Specifically designed to fit around a tracheostomy tube, providing humidified gas directly to the bypassed airway.

  • Face tent: A soft, pliable mask that rests over the chin and extends up over the mouth and nose but does not seal, ideal for patients who cannot tolerate a tighter mask or have facial trauma. It allows for high humidity delivery without skin irritation.

  • Aerosol mask: A contoured mask that covers the nose and mouth, providing a more direct delivery of aerosol therapy compared to a face tent, often used for spontaneously breathing patients.

  • Brigg's T-adaptor: A T-shaped connector used with endotracheal or tracheostomy tubes, often during weaning from mechanical ventilation, allowing aerosol delivery while maintaining an open system for exhalation.

Specific Patient or Situation:

  • These interfaces and the therapy are critical for conditions where the upper airway's natural humidification and filtration are compromised or bypassed.

  • Used post extubation (stridor): Aerosol can help reduce swelling in the upper airway, alleviating stridor.

  • Tonsillectomy: Provides soothing, cool mist to the surgical site, reducing pain and discomfort.

  • Broken jaw, facial trauma, burns: When a conventional mask cannot be used or when there's a need to deliver humidity/medication without direct pressure on sensitive areas.

  • Indicates flexibility to provide aerosol therapy in varied conditions.

  • Intubate patient weaning from ventilator: Provides humidified oxygen during spontaneous breathing trials or after extubation to support recovery and prevent airway drying.

Miscellaneous Equipment:

  • Aerosol heater: Ensures aerosol is at the temperature required for patient needs; increases the temperature of the aerosolized gas, which is crucial for maintaining body temperature, preventing mucociliary dysfunction, and improving patient comfort.

  • Temperature probe: Adjusts temperature of the aerosol delivered; placed near the patient connection to precisely monitor and adjust the temperature (e.g., 37^\circ C) of the delivered aerosol, preventing thermal injury.

  • Oxygen analyzer: Measures the delivered FiO_2 (Fraction of inspired oxygen) to ensure the patient receives the prescribed oxygen concentration, especially important with air-entrainment devices that mix oxygen with room air.

Calculating Total Flow

Formulas and Examples:
Venturi Mask

  • 40% at 6 L/M

  • Total flow calculation:

  • Total Flow = \frac{100}{(100 - 40)} \times 6 = 249

Air Entrainment Large Volume Nebulizer

  • 28% at 5 L/M

  • Total flow calculation:

  • Total Flow = \frac{100}{(100 - 28)} \times 5 = 72.92

  • 50% at 12 L/M

  • Total flow calculation:

  • Total Flow = \frac{100}{(100 - 50)} \times 12 = 24

Further Calculations:

  • 70% at 12 L/M

  • Total Flow = \frac{100}{(100 - 70)} \times 12 = 40

  • 35% at 10 L/M

  • Total Flow = \frac{100}{(100 - 35)} \times 10 = 15.38

Principles and Practice I LAB

Humidity and Aerosol
Goals:

  • Demonstrate the ability to differentiate between different types of humidity: water vapor, aerosol, bland, cool, heated, and medication

  • Discover how to set up and deliver different types of humidity and aerosol medication

Key Terms:

  • Bland aerosol and humidity:

    • Examples include normal saline, saline bullet, hypertonic saline, hypotonic saline

    • Concepts of dissolved vs suspended aerosols

  • Continuous aerosol:

    • Large volume air entrainment nebulizer, sterile water for inhalation, bubble humidifier

  • Therapeutic effects of humidity:

    • Humidity deficit, wick humidifier, Passover humidifier, active vs passive humidity (HME)

  • Aerosolized medication delivery:

    • MDI, DPI, HHN, SVN

    • Particle sizes: 2-5 microns for effective deposition; >5 microns may not be effectively inhaled

    • Medication delivery techniques: valve T-adaptor, heart nebulizer, breath hold, continuous vs intermittent medication delivery

    • Mouthpiece vs aerosol mask usage; HHN with trach collar

Humidity for Invasive Mechanical Ventilation

Types of Artificial Airways in Critical Care:

  • Endotracheal tube: A plastic tube inserted into the trachea through the mouth or nose. It bypasses the upper airway's natural humidification, filtration, and warming functions.

  • Tracheostomy tube: A tube inserted directly into the trachea through a surgical opening in the neck. Also bypasses the upper airway, requiring external humidification.

Bypassing the Upper Airway:

  • Definition: Delivery of air directly to the lungs avoiding upper airway structures, specifically the nasal cavity, pharynx, and larynx, which are natural humidifiers and filters. This bypass necessitates artificial humidification to prevent drying of secretions, mucosal damage, and impaired mucociliary clearance.

Passive Humidity in Invasive Mechanical Ventilation:

  • Setup includes:

    • Heat and moisture exchanger (HME): A passive device placed between the artificial airway and the ventilator circuit. It captures heat and moisture from the patient's exhaled breath and returns it during inhalation, mimicking the function of the upper airway.

  • Rule: HME provides only passive humidity to the airway. It does not actively add water but recycles expired heat and moisture. HMEs are generally suitable for short-term use (e.g., during transport or for patients with stable secretions) but may be less effective for patients with thick secretions or those on prolonged ventilation.

Differences in Active Humidity:

  • May be heated or unheated: Active humidifiers can provide either cool or heated humidification. Heated humidifiers are preferred for invasive mechanical ventilation to maintain normal body temperature, reduce heat loss, and prevent inspissation of secretions.

  • Utilizes an open circuit for air delivery: This refers to the inspiratory limb of the ventilator circuit that's specifically designed to carry heated, humidified gas, often with a reservoir of sterile water.

Importance of Active Passover Heated Humidifier Circuit Components:

  • Temperature probes: Monitor and maintain correct temperatures, typically two are used: one near the humidifier output and one near the patient's airway. These ensure the gas is warmed appropriately and delivered at a safe, consistent temperature (e.g., 37^\circ C at the patient connection point), preventing airway burns or inadequate humidification.

  • Heating wires: Embedded in inspiratory limb to prevent condensation and maintain temperature during inhalation. These wires maintain the gas temperature as it travels to the patient, preventing condensation (rain-out) within the tubing, which can lead to circuit occlusion and potential aspiration risk.

  • Heater/heating plate: Heats water for humidification; the core component that warms the water in the reservoir, generating saturated water vapor.

  • Reservoir: Where sterile inhalation water is stored; must ensure continuous feed. Modern systems often use auto-feed reservoirs to ensure a continuous supply of water, minimizing the need for manual refilling and reducing the risk of contamination.

Noninvasive Ventilation (NIV) with Intermittent Small Volume Nebulizer Aerosol Therapy

Medication Delivery:

  • Example medications and doses for SVN or HHN usage

Acronyms:

  • HHN: Hand Held Nebulizer

  • SVN: Small Volume Nebulizer

Maintaining Circuit Integrity:

  • Importance of minimizing interruptions in NIV to maintain positive pressure and oxygenation

Valve T-adaptor Usage:

  • Allows for aerosol medication delivery without breaking the circuit

  • Should be placed close to the patient for effective delivery

Comparison:

  • Valve T-adaptor vs Brigg's T-adaptor:

    • Discusses differences which affect delivery and patient outcomes