Active Humidification

Maximizing Humidiciation to Improve Patient Outcomes

When patients on mechanical ventilators are trusting you with every breath, providing proper humidification is essential. In cases where the upper airway is bypassed during invasive mechanical ventilation, humidification is necessary to prevent hypothermia, disruption of the airway epithelium, bronchospasm, atelectasis, and airway obstruction.1 Many patients require the use of a heated humidification system to assure that their requirements are met, particularly when a heat and moisture exchanger (HME) is contraindicated or long-term ventilatory support is required.

Clinical Practice Guidelines

In 2012, the American Association for Respiratory Care (AARC) published a new Clinical Practice Guideline: Humidification During Invasive and Noninvasive Mechanical Ventilation.1 The recommendations in this guideline include:

  1. Humidification is recommended for every patient receiving invasive mechanical ventilation.
  2. Active humidification is suggested for noninvasive mechanical ventilation, as it may improve adherence and comfort.
  3. When providing active humidification to patients who are invasively ventilated, it is suggested that - the device provide a humidity level between 33 mg H2O/L and 44 mg H2O/L and gas temperature between 34°C and 41°C at the circuit Y-piece, with a relative humidity of 100%.

The guideline also reviewed the impact of heated wire circuits on optimal humidification. Clinicians should consider that heating the gas between the outlet of the humidifier and the patient Y-piece will decrease the RH of the delivered gas. The magnitude of the decrease will be dependent upon the airway temperature, temperature gradient, and environmental conditions in the immediate patient care area. They note that decreased RH may result in drying of secretions inside the endotracheal tube, with potential risk of its occlusion.1

Therefore, as clinicians strive to deliver optimal absolute and relative humidity levels to invasively ventilated patients in a variety of environmental settings, some condensation will naturally occur and must be drained and discarded.

Clinical Assessments for Optimal Humidification

Managing the heated humidifier is of the utmost importance to clinicians. A heated humidifier’s patient airway temperature, and correlating column temperature, is one of the principle indicators for gauging the amount of humidity being delivered. Once the gas is heated and humidified, the gas passes from the humidifier into the ventilator circuit.

The ventilator circuit has heated wires that maintain the gas temperature to minimize the condensation of the gas (rainout) in the circuit (See Figure 3). According to the 2012 AARC Clinical Practice Guidelines, a maximum delivered gas temperature of 37°C and 100% RH (44 mg H2O/L) at the circuit Y-piece is recommended.1

During routine clinical assessments, it is important to look for a small amount (beads) of condensate in the patient Y-piece and endotracheal tube to ensure optimal humidification. After these assessments, it is important that adjustments can be made to the heated humidifier to deliver optimal humidification to patients undergoing invasive and noninvasive ventilation.

Figure 4: Circuit management with a heated humidifier


  1. Restrepo RD, Walsh BK. Humidification during invasive and noninvasive mechanical ventilation: 2012. Respir Care. 2012; 57(5):782-788. doi: 10.4187/respcare.01766
  2. Branson R. Conditioning inspired gases: the search for relevant physiologic end points. Respir Care. 2009;54(4):450-452.
  3. Chatburn RL, Lough MD. Handbook of Respiratory Care, 2nd ed. Chicago: Yearbook Medical Publishers, 1990:139.
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