Non-invasive ventilation with humidification: the latest evidence

There continues to be a debate as to the effectiveness of applying humidification to noninvasive ventilation (NIV). Some argue that humidification is not indicated because, regardless of the type of mask used (oronasal, nasal, nasal plugs, face mask), air will be humidified by the patient's natural mechanism.  Yet the crux of the evidence says this is not true, and that supplemental humidification is essential.

The last evidence appears in the January, 2014, issue of Respiratory Care, "Hygrometric properties of inspired gas and oral dryness in patients with acute respiratory failure during noninvasive ventilation."  The authors note the following:

Especially when the NIV ventilator uses unhumidified gas, the upper airway can suffer mucosal dryness and airway dysfunction.  The leak compensation applied by NIV ventilators creates high flow throughout the respiratory cycle, which contributes to loss of heat and moisture. About 40-60% of nasal CPAP users with obstructive sleep apnea report nasal congestion, oral dryness, and throat soreness after breahing dry, cold gases.  

They go on to say:

Lack of humidification during NIV is related to greater mucus viscosity and secretion retention, which increases the risk of upper airway obstruction.  Although there are no general recommendations or guidelines conserning humidification during NIV, humidifying devides are commonly applied when NIV continues for more than 24 hours, if pipeline or cycling gas is in the inspiratory gas, or if the patient frequently experiences difficulty in expelling secretions or reports dryness and discomfort."

The authors note the advantages of adding humidification with NIV is that is that it "adds water vapor to the inspiratory gas during NIV," and this, "ameliorates nasal congestion, and improves satisfaction."

There are presently no guideliness for the use of humidification with NIV, although most hospitals have an unwritten rule to apply it to the unit if a patient requires NIV for greater than 24 hours.  While there is no proven ideal temperature, most experts recommend 31° in the heated humidifier and 34° at the Y-piece.

After performing a study of ICU patients of Tokushima University Hospital to determine the effects of humidification on 16 patients (9 male and 7 female) in acute respiratory failure requiring NIV, the authors concluded:

Clinicians should ensure that proper humidification is supplied when patients complain of oral dryness or when little condensation is observed inside the mask.

Keep in mind here that this is one study with analysis by one group of researchers.  Although other studies have come to similar conclusions.  Consider the following:

1. Holland et all concluded that "NPPV delivers air with a low relative humidity, especially with high inspiratory pressure. Addition of a heated humidifier increases the relative and absolute humidity to levels acceptable for nonintubated patients, with minimal effect on delivered pressure. Consideration should be given to heated humidification during NPPV, especially when airway drying and secretion retention are of concern.
2. Rodriquez et al found that heated humidifiers were more effective than a heat and moisture exhchanger (HME)

So, the evidence is abounding that patients who receive NPPV do benefit from heated humidity.  

References:

1. Oto, Jun, Emiko Nakataki, Nao Okuda, Mutsuo Onodera, Hideaki Imanaka, and Masaji Nishimura, ""Hygrometric properties of inspired gas and oral dryness in patients with acute respiratory failure during noninvasive ventilation." Respiratory Care, January, 2014, volume 59, Number 1, pages 39-45
2. Holland, A.E., L. Denehy, C.A. Buchan, J.W. Wilson, "Efficacy of a heated passover humidifier during noninvasive ventilation: a bench study," Respiratory Care, January, 2007, 52(1), pages 38-44, accessed 5/18/14, http://www.ncbi.nlm.nih.gov/pubmed/17194316
3. Rodrigues, Antonia M., Raffaele Scala, Arie Soroksky, Ahmed BaHammam, Alan de Klerk, Arschang Valipour, Davide Chiumello, Claude Martin, and Anne E. Holland, "
   Clinical review: Humidifiers during non-invasive ventilation - key topics and practical implications," Critical Care, 2011, Volume 16, Issue 1, accessed 4/18/14, http://ccforum.com/content/16/1/203