Inhaled Nitric Oxide for Prevention of Postoperative AKI in High-Risk Cardiac Surgery Patients

The goal of this clinical trial is to learn if giving inhaled nitric oxide during heart surgery can prevent acute kidney injury (AKI) in patients who are at high risk of developing this complication. AKI is a serious problem after heart surgery and can lead to longer hospital stays, higher costs, and increased risk of death or long-term kidney disease. Currently, there is no effective medicine to prevent AKI after heart surgery. The main questions it aims to answer are: * Does inhaled nitric oxide reduce the chance of developing AKI within 7 days after heart surgery compared to placebo? * Does inhaled nitric oxide help preserve kidney function up to 90 days after surgery? Researchers will compare inhaled nitric oxide (the device is turned on) to a placebo (the same device is connected to the breathing circuit but not turned on, so no nitric oxide is given). The device panel is covered so that both participants and the research team do not know who receives active treatment or placebo (double-blind). Participants in this study will: * Have the nitric oxide device connected to their breathing circuit during heart surgery; they will receive either active nitric oxide or no nitric oxide (device off) * Provide blood and urine samples to test kidney function during and after surgery * Be followed for 90 days after surgery to monitor kidney health and any side effects