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In adults after major surgery, high-flow nasal oxygen decreases by about two-thirds the need for reintubation compared with conventional oxygen therapy. In this study, only about four in every 100 patients needed reintubation with high-flow nasal oxygen, compared with about 11 in every 100 patients receiving conventional oxygen therapy.

This review evaluated seven randomised and three non-randomised studies in 1,327 adult patients recovering from surgery under a general anaesthetic. Most of the patients were at high risk of reintubation.

As well as reducing reintubation, high-flow nasal oxygen may also reduce the need for additional respiratory support, but the evidence for this is not as strong. There was no difference between high-flow nasal and conventional oxygen therapies in the risk of postoperative lung complications or death.

It remains to be determined which patient groups are most likely to benefit most from this therapy.

Why was this study needed?

General anaesthesia can cause changes to the lungs which may affect the body’s ability to get enough oxygen and remove enough carbon dioxide. If this becomes severe, it leads to postoperative respiratory failure.

The incidence of postoperative lung problems may be as high as 23% after some major surgeries. One in five patients with this complication will die within 30 days of their surgery.

Oxygen therapy is used to prevent or treat postoperative respiratory failure. It involves giving the patient extra oxygen, often through a face mask. A more recent approach has been to use a higher flow of oxygen delivered through flexible tubes placed in the nostrils (a nasal cannula).

Studies have investigated the safety and efficacy of high-flow oxygen, but there have been inconsistent findings. This review aimed to summarise the existing literature to determine whether high-flow nasal oxygen offers any benefit over conventional oxygen therapy.

What did this study do?

This systematic review and meta-analysis included 10 studies of 1,327 adult surgical patients. Seven of the studies were randomised control trials (964 patients), and three were observational studies (363 patients). None of the trials were conducted in the UK.

Three studies were performed after cardiac surgery, five after thoracic surgery and two after mixed surgeries. The risk of reintubation for the participants was considered to be high in most studies.

Starting after post-operative extubation, high-flow oxygen was delivered at between 35 and 60L/minute, and conventional oxygen at between 2 and 10L/minute. In seven studies oxygen therapy was being used to prevent lung complications; in the other three it was used to treat them. Target oxygen saturation varied between 90% and 100%.

Excluding the weaker observational studies from the analyses did not substantially affect the results, increasing confidence in the overall findings.

What did it find?

  • High-flow oxygen therapy cut the reintubation rate by almost two-thirds compared with conventional oxygen therapy, from 11.3% to 3.7% (risk ratio [RR] 0.38, 95% confidence interval [CI] 0.23 to 0.61; nine studies, 1,107 patients). The evidence on this outcome was considered high quality.
  • High-flow oxygen therapy also reduced the need for additional respiratory support (8.6% with high-flow vs 17.3% with conventional oxygen therapy; RR 0.43, 95% CI 0.26 to 0.73; 10 studies, 1,327 people). However, there was moderate variability between studies, and overall this evidence was considered low quality.
  • There was no difference between the groups in postoperative lung complications.
  • Fewer people receiving high-flow nasal oxygen died, but this difference may have occurred by chance (1.2% with high-flow vs 3.7% with conventional oxygen therapy; RR 0.45, 95% CI 0.16 to 1.29; five studies, 942 people).
  • For the subgroup of patients who had cardiac surgery, high-flow oxygen did not reduce the reintubation rate. However, high-flow oxygen did reduce the need for additional respiratory support in this subgroup (RR 0.45, 95% CI 0.25 to 0.81). These analyses included relatively few patients (three studies in 585 people), which may have affected the ability to detect true effects.

What does current guidance say on this issue?

British Thoracic Society guidelines (2017) advise that high-flow nasal oxygen be considered as a potentially superior alternative to reservoir mask treatment in adult patients with acute respiratory failure who are not critically ill, and do not have elevated levels of carbon dioxide in their blood.

A guideline on perioperative care for adults is currently being produced by NICE. It is due to be published in 2020.

What are the implications?

The results of the current review suggest that the use of high-flow oxygen therapy for adult surgical patients after intubation has some benefits over conventional oxygen therapy. Patients may also prefer to use a nasal cannula as it restricts their activities less than a face mask.

Clinicians will still need to consider the parameters for high-flow oxygen therapy and the patient groups who would benefit the most.

Citation and Funding

Lu Z, Change W, Meng SS et al. Effect of high-flow nasal cannula oxygen therapy compared with conventional oxygen therapy in postoperative patients: a systematic review and meta-analysis. BMJ Open. 2019;9:pe027523.

This study was supported by grants from the National Science and Technology Major Project (2017ZX10103004), Key Laboratory of Environmental Medicine Engineering of Ministry of Education, Southeast University; National Natural Science Foundation of China (Grant numbers: 81670074, 81471843, 81871602) and the projects of Jiangsu province’s medical key discipline (ZDXKA2016025).


British Thoracic Society Emergency Oxygen Guideline Development Group. BTS guideline for oxygen use in adults in healthcare and emergency settings. London: British Thoracic Society; 2017.

NICE. Guideline scope: Perioperative care in adults. London: National Institute for Health and Care Excellence; 2019.


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