Transcript for Meet the bystanders who saved lives during the mass shooting in Las Vegas
It makes no sense at all. We go now to the concertgoers who turned into heroes in a matter of seconds jumping in to save their family, friends and strangers and Dr. Jennifer Ashton is in Las Vegas with their stories and what they did right. Good morning, Dr. Ashton. Good morning, Michael. And, you know, yesterday's mass shooting was another example of how quick action at the scene helped to reduce fatalities with a combination of instinct and smart medical moves. Even before the official first responders, emts, police, firefighterses arrived on the scene in Las Vegas, the lives of many caught in the shooting were potentially saved by the first responses of the friends and family immediately near them. I need to help you. I said okay and he dropped the tailgate on some random truck and threw me in there and I was bleeding all over that and took my bell and tied off my leg and kept me from bleeding out. I would have died. Reporter: ABC's Matt Gutman spoke with Mike cronk. What happened to your shirt? Used to compress my buddy's chest. There's blood all over you. There was a lot of wounded people. Reporter: Some jumped in and helped complete strangers. Saw a girl with a wound to the cheek about the size of a quarter and applied pressure and gave her some gauze to put on there. You saw so many people grab each other and go. Reporter: Others came to the rescue before the damage was done. I jumped on my friend, he got hit in the back but I put my arm over him. I'm glad I did. Reporter: In the midst of tragedy many selfless life-saving acts? Just Normal citizens communicating and working together. It was completely horrible but it was absolutely amazing to see all the people come together. And to be clear, Michael, these things that were done yesterday at the scene, they can be taught, they can be learned and they can be practiced. Very important. Something I think that's important for all of us to know. How were ordinary citizens able to save people's lives? Well, ironically they did the right medical things instinctively but it actually there's history to it. It comes out of 2013, something called the Hartford consensus, an initiative brought forth by the American college of surgeons and the first responders to educate people with little or no medical training about what they can do at the scene before the first responders get there and it's called stop the bleed. And basically what it involves is using your hands to compress bleeding, using dressings and if those two fail, using a tourniquet so let me show you what I mean by that. I'll demonstrate on my producer, Robert. Let's say he has an arm wound down here, first thing you do to stop leading is put both hands firmly on the wound apply constant direct pressure and do not take your hands off to look because it will still be bleeding. If that doesn't work or if it's coming out at a high rate, use a shirt. You saw a lot of men walking around without shirts on, they applied their shirt, put their hands over it, same thing. Firm direct pressure until you can get medical attention. In life-threatening hemorrhage you take off a belt, a shoelace, anything that can work. You put it about two to three inches between the wound and the torso, make it real tight and keep it there until you can get to a hospital. This can save lives. We did see how it did save lives. What about first responders, their training and guiding principles. So, again, this has been rehearsed on a local level, on a federal level, on a county level. It's an initiative called threat. It's an acronym that stands for assess the threat and suppress the threat so in an active shooter situation that's what you see, H for hemorrhage control, rapid extraction to safety and then assessment by medical staff and then finally transport and treatment. That can occur on the scene and then it occurs at the hospital or level one trauma center but people do that instinctively but make no mistake the first responders, they have drilled this. They have practiced this and these disaster drills go on in local communities all the time when hospitals put out a need for volunteers, please answer it because if 50 people show up they'll be practicing on 50 people. If 500 people show up it's a better preparation for a disaster drill like this. If we knew that trauma center only had 17 people on average, the most they had and in this case over 100. How do they peep for this kind of mass event? Well, you guys, I just spoke to one of the Seaborn trauma surgeons at umc. He said they were ready and waiting at the door actually for more patients than received. So the way they do it is to get an accreditation as a level one trauma center. The joint commission that oversees all hospitals in this country requires two drys a year minimum, one has to be an internal hospital drill and one has to be what they call an external mass casualty event, a plane crash, a sporting event, a school fire, a mass shooting like this and when they practice those drills, they do it for real and this is why they were able to act so quickly and save so many lives. All right, Jen, thank you so much for that useful information. You have so much dedication. I read the story of one nurse there finished a 12-hour shift, drove back to work 110 miles an hour to do another 12 hours. Another act of heroism, George. Now to ginger.
This transcript has been automatically generated and may not be 100% accurate.