Guidelines covering the subject of humidification during ventilation offer clear goals, but ambiguity regarding the means can be reduced by RT policies.

By Renee Diiulio

A seemingly simple thing, humidity is actually the subject of much controversy. Mention it on a hot summer day and elicit differing predictions about the weather, strong opinions about unbearable levels, and where to find the worst conditions. Mention it in a hospital and get similar, though likely better supported, statements—what is the impact on outcome, what are the right levels to maintain, and how to create the best conditions.

The importance of humidification, at least in medicine, is not questioned. Direct exposure to the average atmosphere results in damage to respiratory tissues that has been noted since the first endotracheal intubation for general anesthesia in the late 1800s.1 For the mechanically ventilated, humidification is standard care. Its use has been shown to prevent hypothermia, disruption of the airway epithelium, bronchospasm, atelectasis, and airway obstruction.2

The American Association for Respiratory Care (AARC) has established clinical practice guidelines that recommend active humidification for every patient receiving invasive mechanical ventilation and suggest it for those utilizing noninvasive mechanical ventilation as well. The association makes seven suggestions in its 2012 publication “Humidification during invasive and noninvasive mechanical ventilation” (following the Grading of Recommendations Assessment, Development, and Evaluation [GRADE] scoring system):2

  1. Humidification is recommended on 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%.
  4. When providing passive humidification to patients undergoing invasive mechanical ventilation, it is suggested that the HME [heat and moisture exchanger] provide a minimum of 30 mg H2O/L.
  5. Passive humidification is not recommended for noninvasive mechanical ventilation.
  6. When providing humidification to patients with low tidal volumes, such as when lung-protective ventilation strategies are used, HMEs are not recommended because they contribute additional dead space, which can increase the ventilation requirement and PaCO2.
  7. It is suggested that HMEs are not used as a prevention strategy for ventilator-associated pneumonia.

The goals are clear, though the methods by which they are to be reached leave room open to interpretation. The document does address specific devices, providing absolute humidity levels for the two common types of humidifier—heated humidifiers (HHs) and HMEs. And it does identify contraindications, but it leaves specific devices and settings to the care provider.

In many institutions, this role is played by the RT, who is often better able than attending physicians to make these decisions. “Physicians depend on the skill and experience of respiratory care professionals to ensure optimal heat and humidity are maintained for patients with artificial airways.”3 The decisions are not, however, left to individual whim but led by guidelines established not only by the AARC but also by the institution.

“Typically, it’s a policy within the RT department. Some institutions are all active or all passive. Some places use passive HMEs for short-term patients and switch to an active device after ‘x’ amount of hours or days. It varies across facilities,” said Kelli McGrew, MS, RRT, senior clinical specialist with Teleflex, Research Triangle Park, NC.

It also varies by patient—“one size does not fit all,” said McGrew. Factors to consider, she notes, include patient demographics, such as age and clinical condition (is there underlying pulmonary disease or an acute pulmonary condition, asked McGrew), the type and expected length of ventilation (eg, invasive versus noninvasive), and additional patient factors that can range from characteristics of secretions to willingness to comply.

The ideal device delivers humidification within these conditions at the desired specifications consistently, with great efficiency, at minimal risk, and with simple ease of use. Of course, much device information is based on bench work, and experts suggest decisions made for the clinical setting should be weighted with such bias in mind, but the bigger issue is dealing with a changing atmosphere, within a room or a patient.

“[Humidifier delivery of 44 mg H2O/L at 37°C] is not a consistently achievable standard given uncontrolled environmental changes, and the presence of unheated portions of the breathing circuit between the end of the circuit wires and the patient. The AARC Clinical Practice Guideline on Humidification During Mechanical Ventilation calls for a minimum of 30 mg H2O/L at 30°C. Even this standard is not consistently met under certain conditions by some HMEs and some HHs,” Ray Ritz, RRT, FAARC, said during a roundtable published by Teleflex on “Selecting the Optimal Humidity for Your Patients.”4

Monitoring Moisture

Monitoring is therefore a routine part of humidifier use. Many devices have built-in alarms to automate this step, helping to streamline workflow and improve care. Routine checks by providers also look for condensate or secretion depending on the type of ventilator, both of which must be cleared. Holt suggests that for HHs, portable bedside hygrometers provide the most accurate picture of the room’s atmosphere.3

Most often temperature, the easiest to measure, is used. The tolerable range is small. The National Guideline Clearinghouse notes that the measurement should be taken near the patient’s airway (or at the outlet port for an HH) and that, per recommendations by the ISO, “the measured gas temperature should be always within ±2°C of the arithmetic mean of the 2 standard temperature sensors in a steady-state condition for the maximum set temperature.”5 McGrew noted temperature should be monitored and alarms in place to detect higher than desired gas temperature.

ResMed of San Diego cited the AARC guidelines regarding monitoring in terms of its manufacturer suggestions. Users are advised to record specific variables when conducting equipment inspections: the humidifier setting, inspired gas temperature, alarm settings, water level and function of any automatic feed system, the quantity and consistency of secretions, and airway obstruction.

Visual inspections are key to system maintenance and use, but each manufacturer provides its own solutions based on accepted guidelines. The more basic are instructions on proper maintenance. ResMed makes recommendations on when to replace the water and parts, such as filters and tubing. The more advanced incorporate new technologies. Teleflex Medical introduced ISO-Gard Circuit Technology into the Neptune Heated Humidifier, creating a closed system with reservoirs integrated into the breathing circuit to collect excess condensate that can then be emptied with a suction wand.

The advances are small but can be mighty. The bigger challenge then becomes not getting too far ahead of the ventilator technology with which humidifiers must work in conjunction to provide excellent care for the patient. With an established need for humidification and few contraindications, the decision to humidify is without controversy. It’s once the water hits the air that questions may arise, but with continued research and smart guidelines, RTs can help guide physicians and patients through the fog.


Renee Diiulio is a contributing writer to RT. For further information, contact [email protected].


  1. Restrepo RD, Walsh BK. Humidification during invasive and noninvasive mechanical ventilation: 2012. AARC Clinical Practice Guideline. Available at:
  2. Al Ashry HS, Modrykamien AM. Humidification during mechanical ventilation in the adult patient. Biomed Res Int. 2014;2014:715434. Available at:
  3. Holt TO. Humidification during mechanical ventilation: current trends and controversies. Clinical Foundations. Teleflex Medical/Hudson RCI. Available at: