Mechanical Ventilation: Humidification (Respiratory Therapy)

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ALERT

Do not use a heat moisture exchanger (HME) for a patient who has thick, copious, or bloody secretions; expired tidal volumes of less than 70%^{undefined#ref3">3} of the delivered tidal volume; a body temperature less than 32°C (89.6°F);³ or high spontaneous minute volumes greater than 10 L/min.³ Do not use an HME for an infant.

OVERVIEW

The respiratory tract heats and humidifies gas entering the lungs, so it is warmed to body temperature and fully saturated with water vapor. The upper airway provides 75% of the heat and moisture supplied to the alveoli.¹ When the upper airway is bypassed by an artificial airway during invasive mechanical ventilation, humidification must be added to the dry inhaled gas.³ Humidity is necessary to prevent hypothermia, disruption of the airway epithelium, bronchospasm, and atelectasis, and it keeps airway secretions thinned. In severe cases, thick airway secretions may occlude the artificial airway or obstruct the lower airways. Two types of humidification systems are available for use with mechanical ventilation: (1) active heated humidifier (HH) and (2) passive HME.

During normal respiration, the humidity in the trachea ranges from 36 to 40 mg H₂O/L,³ and the optimal required moisture below the carina is 44 mg H₂O/L (100% relative humidity at 37°C [98.6°F]).³

Active HHs increase the heat and water vapor content of inspired gas. The humidifier should provide a humidity level between 33 and 44 mg H₂O/L³ and a gas temperature between 34°C and 41°C (93.2°F and 105.8°F)¹ at the circuit Y-piece, with a relative humidity of 100% to prevent the drying out of secretions in the artificial airway.^2,3 A maximum delivered gas temperature of 37°C (98.6°F) and 100% relative humidity (44 mg H₂O/L) at the circuit Y-piece is recommended.^2,3 A relative humidity of 100% may be confirmed by the presence of condensate in the circuit Y-piece connector.³

HMEs operate passively by storing heat and moisture from the patient’s exhaled gas and releasing it to the inhaled gas. There are three types of HMEs: hydrophobic, hygroscopic, and filtered. The HME should provide a minimum humidity level of 30 mg H₂O/L.³ An HME is better than an HH for short-term use (96 hours or less)³ and for use during transport.¹ An HH should be used for patients who exhibit contraindications to HME use or who are on mechanical ventilation for an extended time.

HMEs should not be used on patients with low tidal volumes or increased dead space, ventilation requirement, or arterial partial pressure of carbon dioxide (PaCO₂) levels.

HMEs are contraindicated if the patient has:

• Frank bloody or thick, copious secretions
• Exhaled tidal volume of less than 70% of the delivered tidal volume³
• Body temperature below 32°C (89.6°F)³
• High spontaneous minute volumes (greater than 10 L/min)³

SUPPLIES

See Supplies tab at the top of the page.

EDUCATION

• Give developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, preferred learning style, and overall neurologic and psychosocial state.
• Encourage questions and answer them as they arise.

ASSESSMENT AND PREPARATION

Assessment

1. Find out if the patient and family have health literacy needs or require tools or assistance to effectively communicate. Be sure these needs can be met without compromising safety.
2. Review the patient’s and family’s previous experience and knowledge of mechanical ventilation and understanding of the care to be provided.
3. Assess the length of time the patient has been or will be on the mechanical ventilator to determine the type of humidification system needed.
4. Assess for contraindications for the use of an HME.

Preparation

1. Make sure that appropriate humidification equipment, such as the humidifier base with alarms, humidification chamber, and sterile or distilled water, or HME, is available.
2. Make sure that the HH is performing according to specifications.
3. Make sure that suction is set up at the bedside and functioning properly.

PROCEDURE

Passive Humidification

1. Place the HME inline between the Y-piece and patient.
2. Observe for condensation in the Y-piece connector.
3. Observe for increasingly tenacious or copious secretions.
4. Observe the patient’s tolerance, including an increase in flow resistance and work of breathing (WOB).

Active Humidification

1. Place the HH chamber on the humidifier base attached to the ventilator.
2. Attach the inspiratory limb of the ventilator heated-wire circuits to the HH chamber.
3. Attach the heated-wire connectors to the circuit to heat the circuit and monitor the circuit temperature.
4. Fill the HH with sterile water to the desired level (if applicable).
5. Turn on the humidifier and select the temperature setting to deliver an inspired gas temperature of at least 34°C (93.2°F) but less than 41°C (105.8°F) at the circuit Y-piece.¹
6. Set the high alarm limit on the HH (if applicable) to no higher than 41°C (105.8°F).³ The HH may have automatic high and low alarms settings.
7. Set the low alarm limit on the HH (if applicable) to no lower than 2°C below the desired temperature at the circuit Y-piece.³
8. Observe for condensation in the Y-piece connector.
9. Observe for increasingly tenacious or copious secretions.
10. Observe the patient’s tolerance, including an increase in flow resistance and WOB.
11. Monitor the inspired gas temperature at the patient’s airway.

MONITORING AND CARE

1. If passive humidification is used, inspect the HME for secretion contamination of the filter or insert; replace them as necessary.
2. Maintain the proper HH temperature settings.
3. Maintain a relative humidity of 100%^1,2 by ensuring the presence of condensation in the Y-piece connector.
4. Routinely inspect the HH device.
5. Remove condensation from the patient circuit as necessary.
6. Maintain appropriate high and low temperature alarm settings (if applicable).
7. Maintain the required water level in the HH.

EXPECTED OUTCOMES

• 100% relative humidity maintained^1,2
• Artificial airway free from obstruction
• Thin, easy-to-remove secretions

UNEXPECTED OUTCOMES

• Thermal injury to the airway
• Artificial airway or lower airway obstruction with mucus secretions
• Alveolar gas trapping
• Increased WOB
• Hypoventilation
• Electric shock hazard with HH
• Accidental tracheal lavage
• Increased airway pressure
• Patient–ventilator asynchrony

DOCUMENTATION

• Education
• Type of humidification system used
• Quantity and consistency of mucus secretions
• Humidifier set temperature
• Inspired gas temperature near the patient’s airway
• HH alarm settings (if applicable)
• Water level and function of automatic feed system (if applicable)
• Unexpected outcomes and interventions

REFERENCES

1. Li, J., Lin, H.-L. (2025). Chapter 39: Humidity and bland aerosol therapy. In J.K. Stoller and others (Eds.), Egan’s fundamentals of respiratory care (13th ed., pp. 808-833). St. Louis: Elsevier.
2. Re, R. and others. (2024). Humidification during invasive and non-invasive ventilation: A starting tool kit for correct setting. Medical Sciences (Basel, Switzerland), 12(2), 26. doi:10.3390/medsci12020026
3. Restrepo, R.D., Walsh, B.K. (2012). American Association for Respiratory Care (AARC) clinical practice guideline: Humidification during invasive and noninvasive mechanical ventilation: 2012. Respiratory Care, 57(5), 782-788. Retrieved January 30, 2025, from https://www.aarc.org/wp-content/uploads/2014/08/12.05.0782.pdf

ADDITIONAL READINGS

Shelledy, D.C., Peters, J.I. (2020). Chapter 6: Ventilator initiation. In D.C. Shelledy, J.I. Peters (Eds.), Mechanical ventilation (3rd ed., pp. 311-366). Burlington, MA: Jones & Bartlett Learning.

Clinical Review: Justin J. Milici, MSN, RN, CEN, CPEN, CPN, TCRN, CCRN, FAEN

Published: March 2025