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NIHR Signal Humidified oxygen linked to increased chest infections

Published on 22 August 2017

doi: 10.3310/signal-000467

More respiratory infections in adults followed the use of humidified oxygen compared with non-humidified low-flow oxygen therapy. Bacterial contamination was common in the humidified oxygen bottles across various hospital departments including respiratory wards.

UK guidelines currently recommend using non-humidified oxygen for adults requiring low-flow oxygen. However, in countries such as China, oxygen is routinely humidified regardless of flow rate to prevent respiratory dryness.  

This review identified 27 trials, most conducted in China. Infection rates were low, less than 2%. There was also no difference in reports of dry nose, throat or chest discomfort.

Adults on long-term, low-flow therapy should continue to receive non-humidified oxygen in-line with UK guidance.

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Why was this study needed?

Long-term oxygen therapy involves the delivery of oxygen for a minimum of 15 hours per day. It helps to maintain blood oxygen levels and reduce feelings of tiredness and breathlessness in people with chronic obstructive pulmonary disease as well as other long-term respiratory conditions, heart failure and cancer. Long-term oxygen therapy is often delivered at a low-flow rate of fewer than five litres of oxygen per minute via soft plastic nasal cannulae.

Oxygen can be humidified with the aim of reducing sensations of dryness in the upper airways. This may be important in high-flow oxygen therapy but the benefit of humidifying low-flow oxygen delivered through nasal cannulae has been uncertain. UK national guidance does not recommend it but some local guidelines support its use. In some countries, such as China and Japan, oxygen is routinely humidified regardless of flow rate.

This review aimed to clarify the effectiveness of humidifying low-flow oxygen. 

What did this study do?

This systematic review identified randomised controlled trials and quasi-randomised trials comparing humidified or non-humidified low-flow oxygen therapy given to adults in hospital.

A total 27 studies including 8,876 adults were pooled in the meta-analysis. Three studies were conducted outside China. Sterile distilled water was mostly used as the humidifier fluid (19 of 27 studies) and oxygen flow rate varied from one to four L/min.

Objective outcome measures included bacterial contamination of the humidifier bottle and the time taken for medical staff to administer oxygen. Subjective measures included nose, throat and chest discomfort.

Common study limitations included the potential for biased group allocation and patients or staff being aware of treatment given. Individual study results varied considerably for most outcomes. The size of any effect demonstrated should be treated with caution; however, the direction of effect, given the contamination of humidifier bottles and the link to respiratory infections, seems plausible.

What did it find?

  • Non-humidified oxygen reduced the likelihood of respiratory infection by almost two-thirds compared with humidified oxygen, with an incidence rate of 1.6% vs. 3.8% (odds ratio [OR] 0.39, 95% confidence interval [CI] 0.21 to 0.73, four studies).
  • There was a high rate of contamination by bacteria in the humidifier bottles. 34.5% of humidified bottles were contaminated compared with 12.9% of non-humidified oxygen container bottles (OR 0.16, 95% CI 0.06 to 0.43, eight studies).
  • There was no significant difference between groups in rates of dry nose or throat, nosebleed, chest discomfort, the smell of oxygen and blood oxygen levels.

What does current guidance say on this issue?

British Thoracic Society guidelines advise that humidification is not required when delivering low-flow oxygen (via mask or cannulae) or high-flow oxygen for short periods. They advise that there is ‘little scientific evidence’ of any benefit from humidified oxygen.

The exception is patients with a tracheostomy tube, where the air is bypassing the nose and throat where it is normally warmed and humidified. Humidification of oxygen is recommended for these people.

People requiring high-flow oxygen for more than 24 hours, who report dryness or discomfort of the upper airways, or who have problems with sputum retention may benefit from humidification.

What are the implications?

The findings support current guideline recommendations that routine humidification of low-flow oxygen offers no benefit and should not be used.  

Almost all evidence was from studies conducted in China, so population and demographic differences might limit applicability to the UK. For example, in some parts of China environmental air humidity may be a relevant factor to consider. One trial found that non-humidification in a dry climate led to more complications.

The low quality of the evidence means that it’s not possible to rule out a benefit of humidification in certain settings or patient groups. 

Citation and Funding

Wen Z, Wang W, Zhang H, et al. Is humidified better than non-humidified low-flow oxygen therapy? A systematic review and meta-analysis. J Adv Nurs. 2017. [Epub ahead of print].

This study received no specific grant from any funding agency in the commercial, public or not-for-profit sectors.

Bibliography

British Lung Foundation. What is oxygen therapy? London: British Lung Foundation; 2017.

Hardinge M, Annandale J, Bourne S, et al; British Thoracic Society Home Oxygen Guideline Development Group; British Thoracic Society Standards of Care Committee. British Thoracic Society guidelines for home oxygen use in adults. Thorax. 2015;70(1):i1-43.

NHS Choices. Home oxygen therapy. London: Department of Health; 2015.

O'Driscoll BR, Howard LS, Earis J, Mak V; British Thoracic Society Emergency Oxygen Guideline Group; BTS Emergency Oxygen Guideline Development Group. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax. 2017;72(1):ii1-90.

Why was this study needed?

Long-term oxygen therapy involves the delivery of oxygen for a minimum of 15 hours per day. It helps to maintain blood oxygen levels and reduce feelings of tiredness and breathlessness in people with chronic obstructive pulmonary disease as well as other long-term respiratory conditions, heart failure and cancer. Long-term oxygen therapy is often delivered at a low-flow rate of fewer than five litres of oxygen per minute via soft plastic nasal cannulae.

Oxygen can be humidified with the aim of reducing sensations of dryness in the upper airways. This may be important in high-flow oxygen therapy but the benefit of humidifying low-flow oxygen delivered through nasal cannulae has been uncertain. UK national guidance does not recommend it but some local guidelines support its use. In some countries, such as China and Japan, oxygen is routinely humidified regardless of flow rate.

This review aimed to clarify the effectiveness of humidifying low-flow oxygen. 

What did this study do?

This systematic review identified randomised controlled trials and quasi-randomised trials comparing humidified or non-humidified low-flow oxygen therapy given to adults in hospital.

A total 27 studies including 8,876 adults were pooled in the meta-analysis. Three studies were conducted outside China. Sterile distilled water was mostly used as the humidifier fluid (19 of 27 studies) and oxygen flow rate varied from one to four L/min.

Objective outcome measures included bacterial contamination of the humidifier bottle and the time taken for medical staff to administer oxygen. Subjective measures included nose, throat and chest discomfort.

Common study limitations included the potential for biased group allocation and patients or staff being aware of treatment given. Individual study results varied considerably for most outcomes. The size of any effect demonstrated should be treated with caution; however, the direction of effect, given the contamination of humidifier bottles and the link to respiratory infections, seems plausible.

What did it find?

  • Non-humidified oxygen reduced the likelihood of respiratory infection by almost two-thirds compared with humidified oxygen, with an incidence rate of 1.6% vs. 3.8% (odds ratio [OR] 0.39, 95% confidence interval [CI] 0.21 to 0.73, four studies).
  • There was a high rate of contamination by bacteria in the humidifier bottles. 34.5% of humidified bottles were contaminated compared with 12.9% of non-humidified oxygen container bottles (OR 0.16, 95% CI 0.06 to 0.43, eight studies).
  • There was no significant difference between groups in rates of dry nose or throat, nosebleed, chest discomfort, the smell of oxygen and blood oxygen levels.

What does current guidance say on this issue?

British Thoracic Society guidelines advise that humidification is not required when delivering low-flow oxygen (via mask or cannulae) or high-flow oxygen for short periods. They advise that there is ‘little scientific evidence’ of any benefit from humidified oxygen.

The exception is patients with a tracheostomy tube, where the air is bypassing the nose and throat where it is normally warmed and humidified. Humidification of oxygen is recommended for these people.

People requiring high-flow oxygen for more than 24 hours, who report dryness or discomfort of the upper airways, or who have problems with sputum retention may benefit from humidification.

What are the implications?

The findings support current guideline recommendations that routine humidification of low-flow oxygen offers no benefit and should not be used.  

Almost all evidence was from studies conducted in China, so population and demographic differences might limit applicability to the UK. For example, in some parts of China environmental air humidity may be a relevant factor to consider. One trial found that non-humidification in a dry climate led to more complications.

The low quality of the evidence means that it’s not possible to rule out a benefit of humidification in certain settings or patient groups. 

Citation and Funding

Wen Z, Wang W, Zhang H, et al. Is humidified better than non-humidified low-flow oxygen therapy? A systematic review and meta-analysis. J Adv Nurs. 2017. [Epub ahead of print].

This study received no specific grant from any funding agency in the commercial, public or not-for-profit sectors.

Bibliography

British Lung Foundation. What is oxygen therapy? London: British Lung Foundation; 2017.

Hardinge M, Annandale J, Bourne S, et al; British Thoracic Society Home Oxygen Guideline Development Group; British Thoracic Society Standards of Care Committee. British Thoracic Society guidelines for home oxygen use in adults. Thorax. 2015;70(1):i1-43.

NHS Choices. Home oxygen therapy. London: Department of Health; 2015.

O'Driscoll BR, Howard LS, Earis J, Mak V; British Thoracic Society Emergency Oxygen Guideline Group; BTS Emergency Oxygen Guideline Development Group. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax. 2017;72(1):ii1-90.

Is Humidified Better than Non-humidified Low Flow Oxygen Therapy? A Systematic Review and Meta-Analysis

Published on 26 April 2017

Wen, Z.,Wang, W.,Zhang, H.,Wu, C.,Ding, J.,Shen, M.

J Adv Nurs , 2017

AIMS: To determine the effects of low-flow oxygen therapy with humidified or non-humidified oxygen in adult patients. BACKGROUND: Although non-humidified oxygen in low-flow oxygen therapy is recommended by many guidelines, humidifying oxygen regardless of oxygen flow has been routinely performed in China and Japan and further studies are needed to evaluate the evidence. DESIGN: A systematic review and meta-analysis that comply with the recommendations of the Cochrane Collaboration were conducted. DATA SOURCES: Studies (1980-2016) were identified by searching PUBMED, EMBASE, Science Direct, Cochrane library, CNKI and Wanfang Database. METHODS: We performed a comprehensive, systematic meta-analysis of randomized controlled trials on the efficacy of humidified and non-humidified low-flow oxygen therapy. Summary risk ratios or weighted mean differences with 95% confidence intervals were calculated using a fixed- or random-effects model. RESULTS: Twenty-seven randomized controlled trials with a total number of 8876 patients were included. Non-humidified oxygen offers more benefits in reducing the bacterial contamination of humidifier bottles, as shown by the mean operating time for oxygen administration and the respiratory infections compared with humidified oxygen therapy. No significant differences were found in dry nose, dry nose and throat, nosebleed, chest discomfort, the smell of oxygen and SpO2 changes. CONCLUSIONS: The routine humidification of oxygen in low-flow oxygen therapy is not justifiable and non-humidified oxygen tend to be more beneficial. However, considering that the quality of most included studies is poor, rigorously designed, large-scale randomized controlled trials are still needed to identify the role of non-humidified oxygen therapy. This article is protected by copyright. All rights reserved.

  • Long-term oxygen therapy is defined as oxygen used for at least 15 h per day in patients with chronic oxygen deficiency (chronic hypoxaemia).
  • Chronic hypoxaemia is defined as a partial pressure of oxygen in the arterial blood (PaO2) of ≤7.3 kPa or, in certain clinical situations, ≤8.0 kPa.
  • Low-flow oxygen systems deliver oxygen at flow rates below the patient's inspiratory flow rate.

Expert commentary

Oxygen therapy is widely used in both the acute and chronic setting and necessitates prescription. This meta-analysis indicates there is a relative dearth of evidence on the value of humidification of oxygen in adults.

The current evidence backs guidelines that we should not humidify low flow oxygen in adults as not humidifying oxygen in this setting does not worsen dry nose and throats, nosebleeds, chest discomfort, or oxygen saturations but does reduce bacterial contamination of humidifier bottles and respiratory infections as well as reduces set up time and cost.

Dr Jamie Duckers, Consultant Respiratory & CF Physician, University Hospital Llandough, Penarth