Hyperlactatemia

The goal of this observational study is to learn whether warming patients before surgery, called "prewarming," affects blood lactate levels (a marker of how well tissues are getting oxygen) and recovery in adults having planned (elective) kidney removal surgery (nephrectomy). The main questions this study aims to answer are: * Does prewarming lower the rise in blood lactate seen during and after surgery? * Does prewarming affect time spent in the intensive care unit (ICU), the need for a blood transfusion, or the rate of complications after surgery? Researchers will compare two groups of adults having this surgery. One group receives brief active warming before anesthesia (the "prewarming" group). The other group does not receive this warming (the "control" group). The anesthesia team decides whether to use prewarming and for how long, as part of routine care; the study does not change this decision. Researchers will compare the two groups to see whether prewarming is linked to lower lactate levels and better recovery. Participants will: * Receive their usual, routine surgery and anesthesia care * Have blood pressure, heart rate, body temperature, and blood tests, including lactate, checked before and after surgery, as already done in routine care * Have their ICU stay, need for blood transfusion, and any complications recorded This study does not add any extra tests, procedures, or blood draws beyond routine clinical care.

The purpose of this study is to investigate whether the elevated circulating lactate levels of individuals with metabolic syndrome are responsible for their reduced lipolysis and glucose tolerance. The investigators will conduct an intervention study in which blood lactate levels will be elevated via intravenous infusion of sodium lactate. State of the art metabolic assessment using stable isotopes and indirect calorimetry will be used to study alterations in fat and carbohydrate metabolism.