During the height of anxiety of the COVID pandemic, I did some training in ICU because a key part of my job is ventilators/ventilating people, and they were worried there wouldn't be enough people in ICU with the skills for an influx of ventilator-dependent patients. At that time, I had to care for a brain-dead patient. It was a super interesting experience. There were two separate intensivists who had to carry out the same assessment independently to conclude that the patient was indeed brain dead. Interestingly, there was one test they carried out in which the patient still flinched, but they both still determined that the patient was brain dead. The most interesting part of the test is when they turn off the ventilator for a long time and then take a blood test. I did a blood gas analysis that showed the patient had blood CO2 (PaCO2) of over 70 mm Hg. Usually, a CO2 level this high would trigger inhalation, but it didn't. So he was declared officially brain dead, and a few hours later, he was taken to the theatre for an organ harvest.