Nursing practice often involves undertaking procedures about which there is debate or uncertainty. In Practice Question we ask experts to determine how nurses should approach these situations
Annette Duck, BSc, RN, is interstitial lung disease specialist nurse at University Hospital of South Manchester Foundation Trust and vice chair of the Association of Respiratory nurse specialists
Oxygen therapy is assumed to dry out the airways. Humidifying all supplemental oxygen administered to patients was routine practice in the 1980s and early 1990s in most North American and European hospitals. It was thought this would prevent drying out of the upper respiratory tract but there was no evidence to support this practice.
Effectiveness of humidification
Campbell et al (1988) compared 99 patients who received humidified oxygen and 86 who received “dry” oxygen via a nasal cannula. All patients received oxygen at 5L/min; 50% described symptoms of dry nose and throat, although there was little difference in the two treatment groups. All symptoms decreased or stabilised over time and there was no significant difference in severity of symptoms between the humidified and non-humidified oxygen groups. The authors concluded that while complaints relating to drying of the mucous membranes were common from patients receiving supplemental oxygen, humidified oxygen did not relieve these problems. Andres et al (1997) confirmed Campbell’s (1988) findings in a blinded, randomised, cross-over study involving 150 medical and 87 surgical patients.
BTS emergency oxygen guidelines (2008) state that humidification is not required for the delivery of low flow oxygen (4L/minute and under) or short term use of high flow oxygen for short periods. It is not unreasonable to humidify high flow oxygen for patients who require it for longer than 24 hours if they report upper airway discomfort due to dryness. This would include patients using a Venturi mask at 35% or greater or nasal cannula with a flow rate greater than 4L/min but some patients can tolerate higher flow rates of oxygen without any problems.
Oxygen that is delivered via a tracheostomy should be humidified as it is introduced directly into the lower airway and bypasses the moistening and filtering effects of the upper airway. The BTS emergency oxygen guidelines (2008) suggest that patients with a tracheostomy can be managed for short periods, such as during an ambulance journey, without humidification.
Humidification for home oxygen concentrators is less of a problem as the concentrator filters oxygen from room air that has a variable humidity.
Changing oxygen devices
For patients who have problems with discomfort associated with oxygen therapy, there are a number of devices that are available that may help to alleviate symptoms. High flow nasal cannulas are now available; these have wider tubing just below the nasal prongs than normal cannula and so reduce the delivery speed of oxygen into the nasal passages. Nasal irritation can be minimised by trying a variety of devices including masks, cannulas and OxyArm - a non-touch arm attached to a headband that can be positioned in front of the nose and mouth.
It is important to ensure that all patients receiving supplemental oxygen therapy are well hydrated, as any post operative patient who is debilitated, infected or acutely ill is prone to dehydration, which can cause the mucous membranes to dry out. This could easily be misinterpreted as a side effect of oxygen therapy if patients have recently been prescribed oxygen as a result of deterioration in their condition.
Humidification and viscous secretions
Humidification may be combined with physiotherapy to help patients who have difficulty expectorating viscous secretions. The BTS (2008) suggest using nebulised normal saline in this situation.
Specialists starting NIV therapy will assess the severity of symptoms and decide whether to add humidification - usually in the form of a heated humidifier added into the ventilatory circuit to minimise upper airway symptoms.
Patients in the community with humidification must adhere to strict cleaning protocols for the humidifiers to avoid pulmonary infection. In most cases, they must replace any water in the humidified system with cool boiled water every day. Community teams must help ensure this practice occurs.
On starting therapy, some patients develop upper airway dryness; no evidence suggests that passing oxygen through a “bubble” humidifier will reduce this but it does become less of a problem over time.
Oxygen should always be humidified if it bypasses the upper airway and is introduced through a tracheostomy tube but it is not routine practice to humidify supplemental oxygen for low flow oxygen via nasal cannula (1-4 L/min). In most cases low flow oxygen can be safely administered to patients via a mask or nasal cannula without humidification, and humidification should only be considered after a variety of oxygen delivery devices have been used.
Andres D et al (1997) Randomised double-blind trial of the effects of humidified compared to nonhumidified low flow oxygen therapy on the symptoms of patients. Canadian Respiratory Journal;4: 2, 76-80
British Thoracic Society (2008) BTS guideline for emergency oxygen use in adult patients.Thorax; 63 (Suppl 6) 1-68.
Campbell E et al (1988) Subjective effects of humidification of oxygen for delivery by nasal cannula. A prospective study. Chest; 93: 2, 289-93.