High-Flow Nasal Oxygen After Cardiac Surgery Fails to Improve Outcomes in Major Trial

What Did the NOTACS Trial Find About High-Flow Nasal Oxygen?

High-flow nasal oxygen (HFNO) therapy delivers heated, humidified oxygen at flow rates of up to 60 liters per minute through specialized nasal cannulae. The technique has gained significant traction in intensive care settings over the past decade, particularly after showing promise in acute respiratory failure and during the COVID-19 pandemic. Its use after cardiac surgery had been increasing based on physiological rationale and smaller studies suggesting potential benefits for oxygenation and patient comfort.

The NOTACS (Nasal Oxygen Therapy After Cardiac Surgery) trial was designed to rigorously test whether this approach would translate into meaningful clinical outcomes. The study enrolled patients identified as being at high pulmonary risk — those most likely to develop respiratory complications after cardiac surgery due to factors such as pre-existing lung disease, obesity, or advanced age. The primary endpoint was survival with maintenance of functional independence, a composite measure that captures both whether patients survive and whether they return to meaningful daily function.

Despite the biological plausibility and encouraging signals from earlier, smaller investigations, HFNO did not demonstrate a statistically significant benefit over standard low-flow oxygen therapy for this primary endpoint. The results represent a significant setback for proponents of routine HFNO use in postoperative cardiac care.

Why Does This Matter for Cardiac Surgery Patients?

Postoperative pulmonary complications — including pneumonia, atelectasis, pleural effusions, and acute respiratory distress syndrome — remain a leading cause of morbidity and prolonged hospital stays after cardiac surgery. According to published literature, these complications affect an estimated 15 to 25 percent of cardiac surgery patients and are associated with increased mortality, longer ICU stays, and higher healthcare costs. The cardiopulmonary bypass process itself can trigger an inflammatory response that compromises lung function, making effective postoperative respiratory support critically important.

The negative result from the NOTACS trial is clinically significant because HFNO had been adopted with increasing enthusiasm in many cardiac surgical centers, sometimes without robust evidence for its specific benefits in this population. While HFNO has demonstrated advantages in other clinical contexts — such as preventing reintubation in medical ICU patients, as shown in prior research — its benefits cannot automatically be extrapolated to the unique pathophysiology of post-cardiac surgery patients. The trial underscores the importance of conducting large, well-designed randomized trials before broadly implementing therapies based on physiological reasoning alone.

What Are the Alternatives for Preventing Pulmonary Complications After Heart Surgery?

With HFNO now shown to be ineffective for improving major outcomes in this population, clinicians will need to rely on other evidence-based interventions. Early mobilization — getting patients out of bed and moving within hours of surgery — has consistently shown benefits for reducing pulmonary complications and is recommended in enhanced recovery after surgery (ERAS) cardiac protocols. Lung-protective ventilation strategies during the operative period, including lower tidal volumes and appropriate positive end-expiratory pressure (PEEP), have also demonstrated benefits in surgical populations.

Preoperative optimization, often called prehabilitation, is another area of growing interest. Programs that include inspiratory muscle training and structured exercise before surgery have shown promise in reducing postoperative respiratory complications. Additionally, careful fluid management and the selective use of non-invasive positive pressure ventilation in patients showing early signs of respiratory deterioration remain important components of postoperative care. Researchers continue to investigate novel pharmacological and mechanical approaches, but the NOTACS trial serves as an important reminder that not every physiologically appealing intervention will prove beneficial when subjected to rigorous testing.