Denver ( CNN ) -- A year ago , 42-year-old runner Victor Carlos never thought he 'd be excited just to see the starting line . But that was before he almost died . In fact , the father of two girls did n't breathe for a month ; a machine pushed oxygen through his body . Now he 's training for another marathon . It all began in December with a bad bout of the flu that led to an acute bacterial infection . By the time he checked into the hospital , Carlos was barely hanging on . `` We walked into the triage , and his oxygen level was only 57 % , and everybody turned a corner , '' Carlos ' wife , Brenda Voglewede , told CNN . Healthy blood oxygen levels are higher than 95 % . Carlos was in deep trouble . He had developed acute respiratory distress syndrome , also known as ARDS . It was slowly killing Carlos by attacking his lungs . `` Not only that , but he had multiple organ failure related to the infection . So his kidneys were not working . His liver was not working . And his bone marrow was failing as well , '' said Dr. Ashok Babu , a cardiothoracic surgeon at the University of Colorado Hospital . Babu had no time to spare . He knew trying to force air into Carlos ' lungs would do more harm than good . But without oxygen , Carlos ' organs would soon shut down . Babu had one shot : a procedure called extracorporeal membrane oxygenation , or ECMO . With this treatment , doctors turn down the patient 's respirator , then insert a special tube through the heart . A pump draws blood from the body , flushes it through an oxygenation machine that removes the carbon dioxide and delivers oxygen back to the heart . It functions as an external lung , without the patient taking a single breath . `` So ( oxygenated blood ) could pass through the lungs , and the lungs did n't have to do anything to it because it was already processed , '' Babu said . `` And what we see on the X-ray is the lungs basically collapse down to nothing . ... They are just resting . We support the patient until the lungs can heal on their own . '' Carlos ' family was told he had a 40 % to 50 % chance of survival . `` Dr. Babu initially said he thought he 'd be on ECMO for a week , '' Voglewede recalled . `` Then the week turned into two weeks . And then he 's just like , 'Well , sometimes you just have to wait these things out . ' `` Babu said , `` Two weeks into it we were all pretty worried that we had this young guy whose lungs just did n't seem to be coming back . At the time , he was the patient we had had on ECMO the longest in the history of our program . '' Two weeks became four . Carlos did n't take a single breath for a month . Then a breakthrough came . `` Somewhat miraculously , his lungs just started to open up on their own , '' Babu said . By that time , Carlos was a shadow of his former self . He had lost more than 30 pounds . `` You can imagine , before going into the hospital you are this active person . Then you go in , they put you under , and when you wake ... you ca n't sit up , you ca n't move your arms up and you look at your legs , and they 're just not there anymore , '' Carlos said . `` Then you realize it 's far worse than you ever expected it to be . '' Still , he was determined to make a full recovery . Seven weeks after entering the hospital , Carlos got to go home . `` I started out just walking a block and then pushing that out the following day to a block and a half , or two . Then it was like walking to school with the girls , '' he said . Remarkably , just six months later , Carlos is running . `` My goal at the time was to be able to jog nonstop for three miles . And I did n't think that was going to happen until November . That happened in May , '' he said . Once he was able to cover three miles , the distance he usually started out at to train for a marathon , `` that 's when I knew it was just a matter of time . '' Carlos has set his sights on completing the Denver Rock ' N Roll Marathon on October 20 . He 's already covered the 26.2 miles in a training run . Carlos is n't running for time . He 's running just because he can . `` Every long run gets a little emotional for me this time around . I think of all the people who were there when I could n't do it for myself . I think of the nurses , people at work , my boss who sent cards ... neighbors , friends , family , all praying for me , '' he said . Watch Erin Burnett weekdays 7pm ET . For the latest from Erin Burnett click here .
Victor Carlos got the flu , then an acute bacterial infection , then an illness that attacked his lungs . When he checked into the hospital , his blood oxygen level was at 57 % . He had a fever of 103 degrees and could not breathe properly for several days. Carlos took his first breath four weeks later and is now training for a marathon .