A Single Centre Study Comparing Continuous Interstitial Fluid Lactate Detection to Standard Measurements of Lactate in Patients Undergoing Elective Coronary Artery Bypass Graft Surgery and/or Valve Replacement.

The main goal of this study is to see if a wearable device can reliably track changes in lactate levels in the body. We\'ll compare the device\'s readings to standard blood tests to ensure accuracy. If successful, this device could reduce the need for frequent blood tests during surgery recovery, making patients more comfortable. It might also be useful in emergency rooms for quick diagnoses, especially for patients with chest pain. This study will take place at Barts Hospital with patients having planned coronary artery bypass graft (CABG) and/or replacement valve surgery. Participants will wear the sensors on their upper arm, during which the sensors will continuously measure lactate levels. Participants will also have hourly blood samples taken. In the future, the data from this new device will be used to train computer algorithms to provide quick responses that help manage a patient\'s condition, improving future medical care and technology.