Tissue oxygen and complications: a study of 124 patients

An observational study in the British Journal of Anaesthesia followed 124 adults having major non-cardiac surgery under general anaesthesia. It measured tissue oxygen saturation (StO₂) at the base of the thumb throughout the operation and for two hours afterwards. The lowest StO₂ value was inversely associated with a composite of serious complications and 30-day mortality.

What StO₂ is and why it differs from SpO₂

SpO₂, measured by a fingertip pulse oximeter, reflects oxygen in the blood. StO₂, measured with near-infrared spectroscopy (NIRS), reflects oxygen available in the tissues.

A patient can have normal SpO₂ and low StO₂: the blood is oxygenated but the microcirculation is not distributing it well.

For every 5% increase in minimum StO₂, the estimated odds of a major complication were lower (odds ratio 0.82; 97.5% confidence interval 0.67–1.00). Average StO₂ over time was not associated with complications, and neither measure was associated with wound complications and infections, the study's secondary outcome.

Measured during surgery, not before

In this study StO₂ was measured in the operating theatre and for two hours afterwards, not in the weeks before surgery. The authors write that this is an observational association, and that it remains to be shown whether raising tissue oxygenation improves outcomes.

The study did not assess exercise or other ways of preparing for surgery: how to prepare is decided by the care team.

The Digital Twin lines up the data your devices write to your phone, such as steps, heart rate and sleep, and shows you how they change over time. It does not measure oxygen in the tissues and it does not diagnose: this research describes groups of people, not you. These are data to read together with your doctor.