Effect of Preoperative Prewarming on Serum Lactate Levels in Patients Undergoing Elective Nephrectomy

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.

Inclusion Criteria: * Scheduled for elective nephrectomy * Adults aged 18-90 years * ASA (American Society of Anesthesiologists) physical status classification I-III * Signed informed consent form Exclusion Criteria: * Emergency nephrectomy * Concurrent additional major surgical procedure planned in the same session * Age under 18 or over 90 years * ASA physical status classification IV or higher * Incomplete preoperative records (missing pre- or postoperative measurement of at least one primary outcome variable)