Is humidified better than non-humidified low-flow oxygen therapy? A systematic review and meta-analysis

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 8,876 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 tends 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.