Humidification Delivery

Objectives - Operate a large volume nebulizer; provide active humidification; provide passive humidification; explain goals of cool vs warm humidification; identify humidification systems utilized in respiratory care.

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Humidification Systems Overview

Focus Points

• Identify isothermic saturation boundary principles
• Identify goals and purpose of devices used to deliver humidification to large and small airways
• Match appropriate oxygen delivery devices with the correct humidifier:
  • High flow
  • Low flow
  • Invasive and non-invasive ventilation
• Describe bland aerosol delivery via LVN

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Humidity Definitions

• Humidity — water in a gaseous state
• Absolute humidity — actual content of water vapor in a gas measured in milligrams per liter
• Relative humidity — amount of water vapor in a gas compared to the maximum amount possible, expressed as a percentage
• Potential humidity — maximum amount of water vapor a gas can hold at a given temperature

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Normal Humidification Pathway

Nose: Increases humidity and temperature of inhaled air to 50% of BTPS.

BTPS = body temperature 37°C, ambient pressure, and gas saturated with water vapor (relative humidity).

Upper airway/trachea: Increases heat and humidity of inhaled air to 32–34°C and 100% RH.

Isothermic saturation boundary (ISB): Inhaled gas achieves BTPS conditions (37°C and 100% RH) below the ISB.

Isothermic Saturation Boundary (ISB)

• Point in the airways where gas reaches BTPS (37°C and 100% RH)
• Location: 5 cm below the carina at room temperature; approximately the second/third bronchial divisions
• ISB location/position fluctuates:
  • Varies with physical exertion; breathing rate affects temperature
  • Inspired air temperature affects position (cold air)
  • Exercise-induced asthma (EIA) affects the location of ISB

Purpose for Humidity

Reduce humidity deficit:

• Airways exposed to dry inhaled gases
• Leads to thickened (inspissated) secretions
• Decreases secretion mobility

Reduce temperature deficit:

• Airways exposed to cold air increase mucus production

Humidity and temperature deficits result in mucus thickening and airway obstruction.

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Medical Gas and ISB Principles

• Medical gas has zero percent humidity; humidity must be added to all medical gases
• Humidification methods and devices must provide greater than 60% humidity to the upper airways and below to avoid lung injury

ISB principles:

• Inspiration: temperature and RH increase
• Exhalation: temperature and RH decrease
• Below the ISB: temperature and relative humidity remain constant (37°C — BTPS)

Patients with Artificial Airways

Trach and ET tubes bypass the upper airways.

• Humidification and heat must be added to inhaled gases
• Cold and dry air exposure reduces ciliary motility
• Airways become irritated, increasing mucus production
• Secretions become inspissated (thickened from dehydration — mucus plug formation)

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Humidifier Equipment

Factors for Humidifier Effectiveness

• Temperature
• Surface area
• Time of contact
• Thermal mass

Types of Humidifiers

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Passive Humidifiers: Heat and Moisture Exchanger (HME)

Function: Captures exhaled heat and humidity from the patient and returns heat and humidity during inhalation.

Patient hydration status directly affects humidity delivered.

HME Types

HME Indications

• Short-term use for transporting mechanically ventilated patients
• Skilled nursing facilities for up to 1 week
• Tracheostomy patients transported off mechanical ventilation
• Reduced bacterial colonization in ventilator circuits

HME Contraindications

• Thick, copious, or bloody secretions (active humidity indications)
• Body temperature below 32°C (89.6°F)
• Minute ventilation greater than 10 L/min
• Pediatric or neonatal patients (increases dead space)
• COPD patients — increases airway resistance, WOB, and air trapping; worsens acidosis

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Active Humidifiers

Bubble Humidifier

• Used with low flow oxygen devices
• Gas directed below the surface of water via a capillary tube
• Diffuser breaks gas into smaller bubbles, increasing surface area and effectiveness

Heated Active Humidity

Used with patients with artificial airways (endotracheal/tracheal tubes).

Influence of temperature:

• Temperature is the most significant influence on evaporation
• Warm air holds more water vapor than cool air
• Heated water: more molecules escape the water surface (evaporate)
• As air flows through the heated chamber, humidity is added from the humid environment and contact with the warm water surface

Pass-Over Humidifier

Gas flows through a heated chamber; humidity is added from the humid environment and contact with the warm water surface.

• Temperature at 37°C provides 44 mg H2O/L humidity
• Temperature at 31°C provides 30 mg H2O/L humidity
• Used for invasive and non-invasive mechanical ventilation
• BTPS target: 44 mg/L at 37°C

Passover humidifier variations:

Wick Humidifier

• Invasive and non-invasive mechanical ventilation
• Gives the most humidity
• Examples: Concha Therm, wick humidifier systems, wick canister

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Bland Aerosol Therapy

Aerosol — solid or liquid particles suspended in a gas.

Large Volume Nebulizer (LVN)

For LVN as a high-flow oxygen delivery device (FiO2 30%–100%, delivery interfaces), see Oxygen Delivery Devices.

In this lesson, LVN is used as a jet nebulizer that delivers aerosolized water particles to the upper airways:

• Delivers oxygen at selectable concentrations up to 100% at flow rates greater than 100 L/min
• Delivers heated aerosol to patients with artificial airway, such as tracheostomy patients

Cool Aerosolized Water Administration

Indications:

• Treat upper airway inflammation from intubation, trauma, croup, or epiglottitis
• Promotes localized mucosal vasoconstriction and reduces inflammation
• Reduced inflammation relieves upper airway discomfort
• Improves airflow through large airway
• Reduces work of breathing

Warm Aerosolized Water Administration

Indications:

• Prevent injury to large airways from inhalation of improperly conditioned/dry gas
• Preserves motility of the mucociliary escalator
• Increasing gas temperature increases gas carrying capacity of aerosolized water delivered to large airways
• Maintains mucosal hydration when upper airways are bypassed
• Important when trach patients are off mechanical ventilation

Bland Aerosol Therapy Indications Summary

• Presence of upper airway edema
• Laryngotracheobronchitis
• Subglottic edema
• Post-extubation edema
• Postoperative management of the upper airway
• Bypassed upper airway (intubated/trach — heated)
• Need for sputum specimens or mobilization of secretions

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High-Yield Review

Objectives Checklist

• Operate a large volume nebulizer
• Provide active humidification
• Provide passive humidification
• Explain goals of cool vs warm humidification
• Identify humidification systems utilized in respiratory care

Humidification Systems

Key Clinical Points

• ISB: gas reaches BTPS (37°C, 100% RH) approximately 5 cm below the carina
• Medical gas has 0% humidity; provide greater than 60% humidity to avoid lung injury
• Cool bland aerosol: upper airway inflammation and vasoconstriction
• Warm bland aerosol: prevent dry gas injury; preserve mucociliary escalator when upper airway is bypassed
• HME contraindicated with copious secretions, MV greater than 10 L/min, COPD, and neonatal/pediatric patients