Study finds no benefit of high‑flow oxygen after cardiac surgery

A large international trial has shown that high‑flow nasal oxygen therapy does not improve recovery outcomes compared with standard oxygen therapy in patients at increased risk of respiratory complications following cardiac surgery.

These findings come from the NOTACS Trial (Nasal High-flow Oxygen Therapy After Cardiac Surgery), a large multicentre randomised clinical trial investigating recovery in higher risk cardiac surgery. Royal Brompton Hospital was a key participating site in this international collaboration across the UK, Australia and New Zealand, with Dr Nicoletta Zimbler, consultant anaesthesia and critical care, leading the local study team.

The results have now been published in the JAMA Network Open journal.

After cardiac surgery, many patients need extra support to help them breathe while their body recovers from the effects of surgery and anaesthesia. Oxygen therapy is commonly used to ensure the body receives enough oxygen to support healing and reduce strain on the heart and lungs. The most common approach is standard oxygen therapy (SOT), which delivers oxygen through a face mask or small tubes placed just inside the nose.  

In recent years, high-flow nasal oxygen therapy (HFNOT) has been widely adopted following cardiac surgery. HFNOT delivers warm, humidified oxygen at higher flow rates, which can make breathing easier, improve comfort, help keep the lungs open and support the clearance of mucus. These physiological benefits have led to its routine use in many hospitals, despite ongoing uncertainty about whether it improves longer‑term recovery for patients compared with standard oxygen therapy.

Until now, there has been uncertainty about whether HFNOT provides meaningful clinical benefits compared with standard oxygen therapy, particularly when considering its higher costs and resource requirements after surgery. The NOTACS Trial was designed to address this gap in evidence.

In this trial, a total of 6,538 patients were screened, with 1,280 patients from 17 centres ultimately randomised into two groups. All participants had undergone cardiac surgery and had at least one additional risk factor for respiratory complications, such as asthma, a history of heavy smoking or a recent chest infection. Immediately after surgery, patients received either HFNOT or SOT for a minimum of 16 hours.

Rather than focusing solely on clinical measures, the study prioritised patient-centred outcomes and recovery. The main outcome measure was the number of “days alive and at home without extra support” during the first 90 days after surgery (DAH90), a measure designed to reflect real‑world recovery and independence. Recovery information was collected through questionnaires at 30 days and 90 days after surgery.

The results showed no significant difference between the two groups. Patients who received HFNOT did not experience an increase in the number of days alive and at home without additional support, compared with those who received SOT. Overall, both groups had similar outcomes, with most patients requiring some level of support during their recovery.

A further paper is set to be published regarding the health economics of this study.

When asked for comment, Dr Nicoletta Zimbler said: 

“Thank you very much to the great team who worked so hard, Elizabeth Mittoo from recovery, and the research team, Zohreh Farzad, Kevin Kirby and Annashyl West.”

To find out more about our research, please contact the research team.