Reducing oxygen for critically ill patients does not harm chances of survival, study shows

A national intensive care trial is informing how much oxygen patients should be given to boost their recovery.

Reducing supplementary oxygen given to intensive care patients does not deliver any clear and obvious health benefits, according to new research. It also found that it does not harm their chances of survival.

The National Institute for Health and Care Research (NIHR) funded the UK-ROX trial. It is the largest ever trial of intensive care oxygen therapies outside of the COVID-19 pandemic.

The trial was led by researchers at the University of Plymouth and the Intensive Care National Audit & Research Centre (ICNARC). Southampton’s Professor Mike Grocott was a co-investigator. He was also involved in the trial’s design.

Results have been published in the JAMA journal.

Breathing support

Each year, around 184,000 patients are admitted to NHS intensive care units (ICUs). Over 30% need breathing support. They are given extra oxygen through mechanical ventilators.

However, there is insufficient evidence to guide the use of oxygen. Administering too much, or too little, oxygen may not deliver the intended benefits. It could even cause the patient additional harm.

UK-ROX is the largest ever clinical trial of oxygen use in UK ICUs. Researchers recruited 16,500 patients across almost 100 intensive care units at UK hospitals.

They then sought to find out whether a strategy of conservative oxygen therapy would reduce mortality rates among ICU patients. This involved delivering less oxygen to maintain a person’s oxygen saturation at around 90%.

Providing new evidence

The results showed there was no statistically significant difference in patient outcomes. 35.4% of patients receiving conservative oxygen therapy died within 90 days of their admission. This is compared with 34.9% of patients receiving usual oxygen therapy.

As a result, the research team believe it is safe to allow oxygen levels to be lower in ICU patients. However, it may not necessarily be better for them in terms of survival.

They say there is a need to develop and evaluate more personalised therapies based on a person’s specific medical conditions.

Professor Daniel Martin OBE is Professor of Perioperative and Intensive Care Medicine at the University of Plymouth and a Consultant at University Hospitals Plymouth NHS Foundation Trust. He is co-chief investigator of the UK-ROX trial.

Professor Martin said: “Administering supplemental oxygen through mechanical ventilation is a standard course of treatment for many of those admitted to intensive care. However, there is insufficient evidence to guide us on what oxygen levels deliver the greatest benefits or have the potential to cause harm.

“The results of this study show that reducing supplementary oxygen results in no overall benefit or harm to the patients. That doesn’t mean it is not important for intensive care patients. On the contrary, it means that we will have to come up with ways of determining how much oxygen an individual patient needs. We have to deliver it to them in a precise way if we are to improve patient outcomes.”

Improving patient care

Paul Mouncey, Co-Director of ICNARC, was the other co-chief investigator of the UK-ROX trial.

Mr Mouncey said: “UK-ROX is the largest individually randomised trial conducted in intensive care in the UK. The study has provided much needed evidence to inform clinicians in their day-to-day management of patients.

“A study of this size was only possible by using routinely collected data held within NHS England and within the Case Mix Programme, the national clinical audit of adult critical care in England, Wales and Northern Ireland. We would like to thank the 97 NHS hospitals and 16,500 patients and their families for taking part in the clinical trial.”

Co-investigator Professor Mike Grocott is Director of the NIHR Southampton Biomedical Research Centre.

Professor Grocott added: “This landmark study clarifies the safety of administering lower levels of oxygen to critically ill patients. Understanding how to individualise oxygen therapy will be the next step in improving patient care.”

Professor Martin and Mr Mouncey have presented the results of the UK-ROX trial to delegates at the Critical Care Reviews Meeting 2025 in Belfast.

UK-ROX was delivered at a fraction of the usual cost (around £100 per patient) of a randomised control trial. This shows that clinical trials can be conducted differently and cost-effectively. This is important in an increasingly challenging financial climate.