Hydration and humidification

Hydration and Humidification

The effectiveness of the mucociliary escalator is dependent on appropriate temperature and moisture levels within the airway (Williams et al 1996).

Optimum functionality of mucociliary clearance requires a temperature of 37 °C and an absolute humidity of 44 mg/dm³ corresponding to a relative humidity of 100%. Humidity levels below 50% change the particle size making the mucociliary escalator less effective (Williams et al 1996). The ciliary cells suspend their transport function facilitating pulmonary infection. Airway humidity can be affected by numerous causes, such as infection, tracheostomy, long term oxygen therapy, airline travel, altitude, air conditioning and some medications.

Strategies to assist with airway hydration/humidification at home:

Nose breathing – patients should be encouraged to nose breathe as much as possible

Appropriate fluid intake – patients should be encouraged to drink adequate fluids (unless on fluid restrictions) – it is estimated that a 60 kg person may need at least 2L of fluid per day

Monitor urine colour – which should be pale

Limit intake of caffeine containing fluids – coffee, tea, cola drinks, energy drinks

Sip water regularly throughout the day – don’t rely on thirst

Use the shower to do deep breathing exercises

Steam inhalations when required

Chronic dehydration is associated with an increased risk of:

bronchopulmonary disorders


urinary tract infections and kidney stones


impaired cognitive function

Nebulised saline:

Some patients, either due to fluid restrictions or to the viscoelastic properties of their sputum, require further assistance to humidify their airways.

Nebulised saline 0.9% or hypertonic saline 6%-7% may assist with the expectoration of tenacious sputum (Nicolson et al 2012).

Nasal high flow:

Nasal high flow therapy can be used in the hospital and at home with a portable device (Fig. 1).
Fig. 1 Nasal high flow at home with a portable device

It can be used with both humidified air or oxygen and is administered via wide bore nasal prongs at 37degC.

At a flow rate of 40 L/min with the mouth closed, nasal high flow may provide up to 5cm of CPAP. This is particularly beneficial for patients with a co-morbidity of COPD who may have dynamic hyperinflation and an increase in work of breathing.

Nasal high flow may be indicated for the following patients:

During an exacerbation

Tenacious sputum where other therapies have failed

Chronic sinusitis and consequent dehydrated airways with persistent lower respiratory exacerbations

Elderly, who are unable to exercise, with difficulty expectorating sputum

A study in 2010 by Rea et al demonstrated that the use of nasal high flow for 1-2 hours per day over a 12 month period significantly reduced exacerbation days, increased time to first exacerbation, improved lung function and enhanced quality of life in patients with bronchiectasis compared to patients who received usual care.