Oxygen Levels After Cardiac Arrest: What a Major ICU Trial Found

The findings come from the LOGICAL trial, published in the New England Journal of Medicine (NEJM). The study looked at adults who were unresponsive and being kept alive by a mechanical ventilator in intensive care units (ICUs) after suffering a cardiac arrest — when the heart stops beating. Researchers compared two approaches: conservative oxygen therapy, where oxygen levels are kept closer to the minimum needed, and liberal oxygen therapy, where higher concentrations are given.

The trial found no meaningful difference between the two groups in survival rates or in how well patients recovered their ability to function afterwards.

The question matters because oxygen, while essential, can cause harm in high doses — a process called hyperoxia — and ICU teams have long debated whether dialling it back improves outcomes for the most seriously ill patients. This trial suggests, at least among this group, that it doesn’t — but it also doesn’t make things worse.

For patients and families, the practical message is straightforward. ICU clinicians already tailor oxygen levels to individual patients, and this research adds to the evidence base they draw on. It doesn’t signal a change in what people should expect from emergency care.

The NEJM is one of the world’s most closely watched medical journals, and results published there routinely inform clinical guidelines. Whether UK bodies such as the National Institute for Health and Care Excellence (NICE) or the Intensive Care Society will review their guidance these findings is not yet known.

Anyone with concerns about heart health or emergency care can contact NHS 111 for non-urgent advice, or call 999 in an emergency.