A single centre study comparing continuous interstitial fluid lactate detection (as measured by change in current) to standard measurements of change in venous and arterial lactate in patients undergoing elective coronary artery bypass graft surgery and/or valve replacement.

A small sensor worn on the upper arm could replace the need for frequent blood draws to measure lactate levels in patients recovering from heart surgery. Lactate is a key marker of how well tissues are getting oxygen, and doctors currently track it by taking hourly blood samples from a vein or artery. This is painful, invasive, and labour-intensive. The study tests whether a continuous interstitial fluid sensor—similar to a continuous glucose monitor—can accurately track lactate changes in patients undergoing planned coronary artery bypass graft or valve replacement at Barts Hospital. Participants will wear the sensor while also having hourly blood tests, allowing direct comparison. If the device proves accurate, it could make post-surgical recovery more comfortable by reducing needle sticks. Beyond the ward, the same technology might speed up triage in emergency rooms for patients with chest pain, where rapid lactate readings can flag serious conditions. The data will also be used to train computer algorithms that could eventually alert clinicians to deteriorating patients in real time. This is a practical, near-term clinical trial—not fundamental science—aimed at replacing an existing invasive test with a wearable alternative.