The doctor who was accused of murdering patients in New Orleans as Katrina approached (fortunately, the grand jury refused to indict her) recounts the heart-wrenching facts of those days in Time.  A snippet:

In normal triage situations, the sickest people are treated first. But my understanding is that conditions were so bad, you and the other medical staff switched to a reverse triage or battlefield approach. Tell me about this.
The conditions were unbearable. Inside the hospital it was pitch black, with odors, smell, human waste everywhere. It was very rancid. You would take a breath in and it would burn the back of your throat. The patients were very sick. That’s when we had to go from triage to reverse triage because we came to realize if patients aren’t being evacuated, [we had to deal with what we had]. Basically it was a general consensus that we’re not going to be able to save everybody. We hope that we can, but we realize everybody may not make it out.

What were the categories?
We divided patients into groups one, two and three. Patients in category one are able to sit up and walk and are not very sick. Patients in three are critically ill, “Do Not Resuscitate.” The ones in category two were sick, but doing much [better than those in category three]. The triage system was very crude—we’d write the number 1, 2 or 3 on a sheet of paper and tape it across the patient’s chest with their hospital records. There was limited use of flashlights. There were limited batteries. [Parts of the hospital] were pitch black. I’m talking jet black. Very dangerous. It was pitch dark in inner rooms.

What is the reverse triage process like?
Let me tell you, for a patient to be triaged—typical triage isn’t that difficult. Reverse triage is heart wrenching. Absolutely heart wrenching. You place patients into categories. With boats coming and going we could evacuate patients who could sit. There were elderly couples—how do you make that decision who can go when one was sick and the spouse wasn’t? Do you let elderly couples go together as husband and wife? Some of these couples had been married 50 years.

I can’t possibly imagine what it must have been like, as a doctor, to be called upon to make decisions about who is to live and who is to die.