Boston was All In to Save Lives: The Finish Line and the Hospitals.

"The bombs at the Boston Marathon were designed to maim and kill, and they did. Three people died within the first moments of the blast. More than a hundred and seventy people were injured. They had their limbs blown off, vital arteries severed, bones fractured, flesh torn open by shrapnel or scorched by the blasts’ heat. Yet it now appears that every one of the wounded alive when rescuers reached them will survive." 
APRIL 17, 2013 WHY BOSTON’S HOSPITALS WERE READY POSTED BY ATUL GAWANDE- New Yorker Blog

The tragic events at the Marathon occurred within yards of the medical tent and hundreds of the best caregivers in the world. I have not run another big city marathon in many years but have run St. George 3 times with 7000 competitors. St. George puts a very active medical presence on the course to intersept those in trouble and has a relatively light medical presence at the finish line. You finish, go under a mister, are handed a bottle of water and directed into a grass corral with hundreds of others to fend for yourself, often in tremendous heat. Not that EMT's aren't around but you are pretty much on your own.

Boston, for those who haven't run it makes finishers walk a couple hundred yard (at least it feels that way), very friendly gauntlet of medical people and volunteers. No stopping for any length of time beyond picking up a water bottle, mylar, medal, food. If you can't walk and need help they are there in an instant with wheelchair and helping arm.

The fact that hundreds of some of the best medical people in the world, EMT's, police, race volunteers, finishing runners with training, and passerby were there at the site of the bombings and went into action in seconds going from tending a few blisters and dehydration to setting up a battlefield triage and tending to gravely injured is truly amazing. Within 5-10 minutes all the injured were being treated and sent to hospitals.

The heroic care continued of course at the hospitals. And here the story is equally amazing. Please read the full NewYorker article here. The hospitals had drilled for such a mass event but it was so large, so sudden, and so devastating that no direction was really possible. Everyone knew what to do:  hundreds showed up immediately, nurses watching the news decided how to stock multiple operating rooms based on anticipated injuries, teams formed with multiple specialists for each patient.

All the injured who were alive when reached by rescuers are still alive and we pray it stays that way.

From the article written Atul Gwande, a doctor at one of the hospitals, reflecting on the post 9/11, Newtown, Aurora, Iraq and Afghan wars world:

"We’ve learned, and we’ve absorbed. This is not cause for either celebration or satisfaction. That we have come to this state of existence is a great sadness. But it is our great fortune.

Last year, after the Aurora shooting, Ron Walls, the chief of emergency medicine at my hospital, gave a lecture titled “Are We Ready?”

In Boston, it turns out we all were."