Why bun, creatinine, and electrolyte ordered with a patient on a ventilator in ards?

Check kidney fxn. In the ICU all organ systems are monitored to see if other interventions are required. These tests look at the kidney and the things that kidneys regulate to ensure that dialysis or medications are not needed.
Needed labs. When on a ventilator in the icu, you need to follow the labs - such as bun, creatinine, and electrolytes - very closely, because due to the illness, various treatments, and other unforseen events, the labs may indicate complications. So, every day, usually, these labs are checked and corrected if necessary.