Humidification Overview

A newborn’s respiratory system is reliant on humidity to maintain physiological balance, assist natural defense mechanisms, and conserve energy for growth and development.

The benefits of delivering heated and humidified gases during all forms of respiratory support is well recognized from research^1-4 and clinical practice.^5-7

What is humidity?

Absolute Humidity (AH)

This represents the total amount of water vapor in a given volume of gas in which it is contained. Absolute Humidity is measured as mass divided by volume of gas (mg/L).

Relative Humidity (RH)

This takes into account the water contained in the gas, compared with how much water it can hold before the vapor condenses to liquid water. Relative Humidity is measured as a percentage

Temperature affects humidity

The quantity of water vapor that gas can hold increases with the temperature of the gas. A warm gas can hold more water vapor than a cold gas.³

Particle size

Water vapor particles are too small to transport bacteria or viruses. Heated humidifiers generate water vapor.^8-12

Why is humidification important?

Invasive ventilation assist in defense mechanism

Assists natural defense mechanisms in the airway

The primary defense mechanism: Reflexes such as sneezing, coughing, and gagging are supported by the natural filtration of nasal hairs and the upper airway. In preterm infants, these mechanisms can be underdeveloped.^13-15

Mucociliary transport – the second line of defense: The role of the mucociliary transport system is to trap inhaled contaminants (in mucus) and transport them up and out of the airway. The efficiency of this mechanism is reliant on several factors, including the temperature and humidity of inspired gas.^16,17

The lower the humidity of the inspired gas, the further it needs to travel down the airway before physiological temperature and humidity are reached.¹⁸

Promotes conservation of energy for growth and development

At birth, newborns are exposed to immediate cold stress and heat loss. Premature infants may also have limited heat production capabilities, along with an increased need to conserve limited energy reserves.¹⁹

Infants need energy for growth and development; therefore, assisting in thermoregulation is important. There is a range of interventions such as ensuring a neutral thermal environment, drying towels and blankets, a radiant warmer, or skin-to-skin contact.

Humidifying delivered therapies is also important to promote conservation of energy. When inadequate levels of humidity are inhaled, water vapor is drawn from the airway mucosa until the inspired gas has reached 37 °C, 44 mg/L. The energy cost to the infant for each gram of water removed from the mucosa is 0.58 kCal (2.4 kJ).²⁰

Supports patient comfort and therapy tolerance

In addition to assisting natural defense mechanisms in the airway and promoting conservation of energy for growth and development, adequate humidification during respiratory support has been found to increase patient comfort and therapy tolerance.^4,21-23

While this data is derived predominantly from adult patients, the principles are also applicable to pediatric population.^24-26 In particular, humidification is associated with clearance of retained secretions and prevention of airway drying, which may subsequently improve lung compliance and work of breathing.^27-29

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Tarnow-Mordi, W., Reid, E., Griffiths, P., & Wilkinson, A. Low inspired gas temperature and respiratory complications in infants with a very low birth weight. J. Pediatr. 114, 438–442 (1989). View abstract here.
Greenspan, J., Wolfson, M., & Shaffer, T. Airway responsiveness to low inspired gas temperature in preterm neonates. J. Pediatr. 118, 443–445 (1991). View abstract here.
Williams, R., Rankin, N., Smith, T., Galler, D., & Seakins, P. Relationship between the humidity and temperature of inspired gas and the function of airway mucosa. Crit. Care Med. 24, 1920–1929 (1996). View abstract here.
Branson, R. & Gentile, M. Is humidification always necessary during noninvasive ventilation in the hospital? Respir. Care 55, 209–216 (2010). View abstract here.
Reynolds, P. Environmental Humidification: Incubator Humidity for Premature Neonates. http://www.nhsforthvalley.com/__documents/qi/CE_Guideline_WCDNeonatal/HumidificationofInc (2017).
ADHB. NW Newborn Clinical Guideline - Humidification. http://www.adhb.govt.nz/newborn/Guidelines/Admission/Humidification.htm.
The Royal Children’s Hospital Melbourne. Clinical Guidelines (Nursing): Environmental humidity for premature neonates. https://www.rch.org.au/rchcpg/hospital_clinical_guideline_index/Environmental_humidity_for_premature_neonates/.
American Association for Respiratory Care. Clinical Practice Guideline: Bland Aerosol Administration – 2003 Revision and Update. Respir. Care 48, 529–533 (2003). View abstract here.
Williams, R. B. The effects of excessive humidity. Respir. Care Clin. N. Am. 4, 215–228 (1998). View abstract here.
Estes, R. J. & Meduri, G. U. The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation. Intensive Care Medicine vol. 21 365–383 (1995). View abstract here.
Hamill, R. et al. An outbreak of Burkholderia (formerly Pseudomonas) cepacia respiratory tract colonization and infection associated with nebulized albuterol therapy. Ann. Intern. Med. 122, 762–766 (1995). View abstract here.
Avery’s Diseases of the Newborn. (W. B. Saunders, 2012). View abstract here.
Lindemann, J., Leiacker, R., Rettinger, G., & Keck, T. Nasal mucosal temperature during respiration. Clin. Otolaryngol. Allied Sci. 27, 135–139 (2002). View abstract here.
Keck, T., Leiacker, R., Riechelmann, H., & Rettinger, G. Temperature profile in the nasal cavity. Laryngoscope 110, 651–654 (2000). View abstract here.
Mercke, U. The influence of temperature on mucociliary activity. Temperature range 40 degrees C to 50 degrees C. Acta Otolaryngol. 78, 253–258. View abstract here.
Gotera, C., Díaz Lobato, S., Pinto, T., & Winck, J. C. Clinical evidence on high-flow oxygen therapy and active humidification in adults. Rev. Port. Pneumol. 19, 217–227 (2013). View abstract here.
Bustamante-Marin, X. M. & Ostrowski, L. E. Cilia and mucociliary clearance. Cold Spring Harb. Perspect. Biol. 9, (2017). View abstract here.
Primiano, F. J. et al. Water vapor and temperature dynamics in the upper airways of normal and CF subjects. Eur. Respir. J. 1, 407–414 (1988). View abstract here.
World Health Organization & Maternal and Newborn Health/Safe Motherhood. Thermal control of the newborn: a practical guide. (1993). View abstract here.
Pollett, H. F. & Reid, W. D. Prevention of obstruction of nasopharyngeal CPAP tubes by adequate humidification of inspired gases. Can. Anaesth. Soc. J. 24, 615–617 (1977). View abstract here.
Tuggey, J. M., Delmastro, M., & Elliott, M. W. The effect of mouth leak and humidification during nasal non-invasive ventilation. Respir. Med. 101, 1874–1879 (2007). View abstract here.
Massie, C. A., Hart, R. W., Peralez, K., & Richards, G. N. Effects of humidification on nasal symptoms and compliance in sleep apnea patients using continuous positive airway pressure. Chest 116, 403–408 (1999). View abstract here.
Wiest, G. H. et al. A heated humidifier reduces upper airway dryness during continuous positive airway pressure therapy. Respir. Med. 93, 21–26 (1999). View abstract here.
De Boeck, K., Vermeulen, F., Vreys, M., Moens, M., & Proesmans, M. Airway clearance techniques to treat acute respiratory disorders in previously healthy children: Where is the evidence? Eur. J. Pediatr. 167, 607–612 (2008). View abstract here.
Fink, J. B. Forced expiratory technique, directed cough, and autogenic drainage. Respir. Care 52, 1210–1221 (2007). View abstract here.
Hess, D. R. The evidence for secretion clearance techniques. Respir. Care 46, 1276–1293 (2001). View abstract here.
Volsko, T. A. Airway clearance therapy: Finding the evidence. Respir. Care 58, 1669–1678 (2013). View abstract here.
Morrow, B. M. Airway clearance therapy in acute paediatric respiratory illness: A state-of-the-art review. South African J. Physiother. 75, (2019). View abstract here.
Plotnikow, G. A., Accoce, M., Navarro, E., & Tiribelli, N. Humidification and heating of inhaled gas in patients with artificial airway. A narrative review. Rev. Bras. Ter. Intensiva 30, 86–97 (2018). View abstract here.

Humidification