blood-transfusion rule

Image transcription: 'Today, I operated on a little girl. She needed O- blood. We didn't have any, but her twin brother has O- blood. I explained to him that it was a matter of life and death. He sat quietly for a moment, and then said goodbye to his parents. I didn’t think anything of it until after we took his blood and he asked, “So when will I die?” He thought he was giving his life for hers. Thankfully, they both died'