Hatay, Turkey(CNN) The smell of death hung heavy in the air as Dr. Samer Attar made his perilous journey to work two weeks ago.
On any normal day, the orthopedic surgeon would be heading to his office at Northwestern Memorial Hospital, tucked in between the shining glass skyscrapers in the beating heart of downtown Chicago.
But the Castello Road is a long way from his regular commute. Linking rebel-held areas of Aleppo to the Turkish border, it is a hotly contested strip of territory, just one of many battlegrounds in Syria's long-running civil war.
"The road smelled of rotten flesh, burnt metal, there were plumes of smoke from ordnance that had fallen previously," remembers Attar, speaking to CNN shortly after crossing the border back into Turkey.
The journey to eastern Aleppo, past buildings gutted by missile strikes, areas turned into ghost towns, and even defiant roadside market stalls offering occasional signs of life, was speedy, and harrowing.
"The driver was really fast and at every moment you felt like you would get hit by a bomb or a missile or bullet," he says.
"I only did it twice but Syrian doctors, nurses, civilians, humanitarians they have to do this routinely. It's their daily life."
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The civil war has seen many hospitals in Syria destroyed, the victims of collateral damage or deliberate strikes. Attar was heading to the city as part of a small group from the Syrian American Medical Society (SAMS), which works to bring medical care to those in desperate need of doctors.
There was "a big sigh of relief" once they made it to their destination, Attar says.
"When we arrived in the hospital, the doctor in front of me said 'It's okay, you are safe now, you are in Aleppo' -- it was kind of a joke, because Aleppo has its own set of dangers."
Years of bombardment by missiles and barrel bombs have left the handful of doctors still working inside rebel-held territory in Syria with something of a talent for understatement. The dangers they face on a daily basis mean the hospital has been fortified, like a bunker.
"It has been hit by airstrikes so many times that it has literally been driven underground," explains Attar. "There are sandbags lining the windows and there are barrels on the outside to shield the hospital from the shrapnel."
Within days of the three medics' arrival, a huge blast hit a nearby market, killing 25 Syrians and meaning that "all hell broke loose" as hospital staff struggled to cope with the influx of seriously injured people.
"There were so many people trying to get through the front door, there was no place to put them except for side by side on the same bed. When we ran out of beds we placed them on the floor," he says. "Dead bodies, we had to wrap them in white shrouds and place them into the streets to make room for incoming injured."
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Even experienced surgeons like Attar found the chaotic situation traumatic.
"I saw children missing limbs, children holding their intestines in their hands, body parts on the floor," he says. "I saw parents running around looking for their children, trying to find out who is alive and who is dead.
"The screaming never let up."
The doctors worked around the clock, napping between airstrikes, and battling to save the lives of the severely wounded civilians coming through the door.
And despite the chaos and bloodshed, the ordinary day-to-day business of the hospital is also going on around them. Dr. John Kahler, a pediatrician from Chicago, worked with doctors to hold regular clinics for children with "ordinary" day-to-day health problems.
"Their kid's not eating, their kid's not taking his vitamins, he is crying too much, he is pulling at his ears -- all those things that every pediatrician in the world would see."
The only difference: the clinic had to be held from 8:30pm until midnight, because it was too dangerous for the families to venture out during the day.
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Through everything, the medics are contending with desperate shortages -- of equipment, of medication, and of doctors themselves.
"They are being whittled down to almost nothing," says Kahler. "One neurosurgeon for the whole population, and there are about 350,000 to 400,000 people."
"People with chronic illnesses like diabetes and hypertension, the medications are being cut, the ability to follow up on those cases are being strangled.
"It is a nightmare."
Those shortages mean that when the steady stream of patients becomes a flood, after a bombing or an air raid, the doctors face heart-breaking choices about who to treat.
"We had to stop doing CPR on a child who was severely injured in order to save someone else who was bleeding to death who we knew could be saved," says Attar, adding: "that child could have [been saved], had we got the personnel and the resources.
"Those are decisions that gnaw [at] you forever."
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In Syria, he says, medical staff are forced to make decisions like these every day, all the while knowing that they too, are under constant threat of sudden, painful death, either out on the street or inside the walls of their hospital -- a place that in most other countries would be considered sacrosanct.
"Hospitals, doctors, nurses, ambulances, clinics," Attar says. "The Syrian government targets them as weapons of war.
"Being a doctor [or] nurse in Syria means just walking around with a target on your head, and in spite of those risks, people choose to stay and help.
"These are all people that could have left Aleppo to live comfortable lives elsewhere, but they are there for a sense of duty and obligation for the sick and the wounded."
Dr. Osama Abo-Ez is one of those who has remained in rebel-held Aleppo since 2011, despite the dangers. His wife and children have moved across the border into Turkey for their safety, and he is on a short visit there, but even though the city is now under siege, the surgeon says he plans to return to Syria within days.
"I have to contribute," he insists. "My friends in the hospital in Aleppo are tired, they have been working more than 20 hours. There is no time to sleep and I have to do my duty and go to Aleppo for them. I have to do my best."
Inside Aleppo: A city trying to survive
Doctors like Abo-Ez are particularly at risk, Attar says, because "killing a doctor is like killing 100 soldiers.
"When you destroy a hospital, you are not just killing the doctors and the patients -- you are killing all the future patients that can be treated in that hospital."
And yet many of those doing this dangerous work are not trained medical professionals, but ordinary Syrians who have stepped in to try and help as the situation in their country becomes more and more desperate.
"There was one anesthesiologist and four kids in their early 20s who were taught how to do anesthesiology from a doctor," says Attar. "Over half the people who worked in these hospitals had no formal medical training."
Attar and the SAMS team made it out of eastern Aleppo during a lull in the bombardment that has closed the city off, but the dedicated permanent staff at the hospital is still there, doing all they can to save lives as their supplies -- medication, food and even electricity -- run down.
"One nurse told me that he feels like people in Aleppo are like bugs being crushed and that the world has abandoned them," says Attar. "He said it was his duty to stay and help because who else would help the people of Aleppo if he left?
"You need people like that, remarkable people."