In the intensive care unit last night, I did something I’ve never done before: replaced a patients entire blood volume with fresh, new blood. It’s called an exchange transfusion — literally, your goal is to exchange as much of a patient’s blood volume as you can with new blood. And when I say that I did it, I mean that on every day of the week but Saturday, my hospital has machines to do this procedure, but on Saturdays, it’s the resident who has the privilege of moving all that blood into and out of the patient. For four and a half hours, it was my job to draw off 165 milliliters of blood from my patient’s arterial line every 10 minutes, as bag after bag of fresh blood dripped into a intravenous line in his other arm.

By the end of the first hour, I had it down to an exact science; I could get the 165 ml off in four minutes, leaving me with a luxurious six more minutes to rush around the ICU taking care of my other patients before I had to be back at his bedside to repeat the cycle. By the end of the second hour, the novelty had long worn off, and I was cursing my hospital for not having the mechanized exchange machine available. (I was also growing curious about the three or four plastic urinals full of discarded blood that had already accumulated at the foot of the bed.) By the end of the full four and a half hours, I was just amazed at what we had done — taken over four liters of blood out of a fifteen year-old boy, and replaced it with blood that had been donated by over a dozen people, none of whom could know that they were helping this young man avoid going onto a ventilator. This morning, the patient was saying that he felt a lot better; given how much manual labor went into the procedure, that made me feel a lot better, too.