Doctors seek better evidence for safe oxygen limits


Oxygen is vital to life, but too much is toxic. This is especially true for patients under general anaesthetic, yet there remains a lack of reliable evidence on how much is too much. Now Southampton researchers Dr Alex Oldman and Dr Andrew Cumpstey are working to give anaesthetists the answers they need.

We need oxygen to survive, but in high concentrations it’s toxic and can even be fatal. Anaesthetists have the challenge of striking the right balance to keep us safe.

“If oxygen levels drop too low, you’ve got less than three minutes before the brain is permanently damaged,” explains Dr Cumpstey, NIHR BRC Clinical Research Fellow and Specialty Trainee in Anaesthetics.

Yet go too far the other way and the results can include damage to DNA, lung injury and increased risk of a heart attack by making the arteries constrict – with recent research indicating this toxicity starts at concentrations of 60% oxygen.

Awareness of these risks has already changed how oxygen is used. It is now no longer given to patients who’ve had a heart attack, or when newborn babies are being resuscitated.

Troubling revelations

This uncertainty in striking this balance is why the World Health Organisation (WHO) sought to give clear advice by publishing its 2016 guidelines for anaesthetists.

Those guidelines recommend giving oxygen at 80% - a surprise to many in the field given this is four times the level found in normal air, way above the 50% given in most NHS operating theatres currently and in contradiction to many studies.

Surprise turned to dismay when serious flaws were discovered in results from the work of one Italian research group, on which the guidelines drew.

In all, 38 separate published results from this group were found to be compromised. The WHO has downgraded its backing of the guidelines, but the conflicting advice and research findings mean anaesthetists don’t have definitive, reliable evidence to base decisions on.

 “Anaesthetists I speak to about this want to do the right thing,” says Dr Cumpstey. “They just don’t know what the right thing is.”

Clearing things up

Now Southampton researchers Dr Alex Oldman and Dr Andrew Cumpstey are aiming to finally bring some clarity to the issue through two clinical trials aiming to determine safe oxygen concentrations.

The PULSE-OX trial is linking oxygen concentrations given in major abdominal surgery operations with patient outcomes, while the TOXYC trial is investigating the best oxygen level for patients on a life support machine in the intensive care unit.

They hope that the results of their latest trials will help to provide the much needed evidence to support new guidelines, helping anaesthetists to ensure patients stay safe during their operations.

Posted on Friday 24 May 2019