CHICAGO — The hospital where I work in Aleppo, Syria, is in a basement. The building above has been bombarded so many times that the top floors are too dangerous to use. Barrels and sandbags line the entrance to fortify it as a bunker.

Aleppo is a long way from my home in Chicago. That city, too, has its share of human suffering. Any Chicago surgeon who takes emergency duty can attest to the gun violence that plagues local communities. But the hospital where I work has state-of-the-art resources and some of the best doctors and nurses in the world. Scalpels are sharp, operating rooms are sterile, and specialists are abundant.

Aleppo, too, has some of the best doctors and nurses in the world, but there are so few left. They are exhausted, endangered, and they need help. That is why I volunteer for medical work in Syria; even the few weeks a year that I can offer provide some respite for the handful of surgeons who serve a population of 300,000 in a war zone. It is a heavy responsibility, but I feel I cannot ask world leaders to risk their citizens’ lives to save people there if I myself am unwilling to take such risks.

My weeks in Aleppo are intense. In Chicago, where I specialize in surgical oncology, I see one patient at a time. In Aleppo, I see 20 at once. You live your life one massacre to the next: of children at school, or of families sleeping at home or shopping at a market. We hear the jets screech by, the helicopters whirring in the sky, the mortars launching, then the bombs exploding. Followed by sirens and screaming.

The screaming seems never to end, some days. So many people pushing through the entrance. There are never enough beds, so patients have to share gurneys or lie on the floor. Sometimes, there is no place to step, with patients lying on floors smeared with blood and strewn with body parts. There are few field hospitals left in Aleppo, so patients who are stuck outside and can’t make it in sometimes die on our doorstep.

Then, abruptly, it ends. I walk away from all those patients. I am driven through sniper alleys, under airstrikes, and past checkpoints to cross the border into Turkey. From there, I fly home.

It crushes me every time. One moment, I’m in an underground hospital shaking from the blasts of missiles, saving whom we can, watching those we can’t bleed to death. The next moment, I am at the airport coffee shop watching a man in a sharp suit cut the line or a woman berate the barista for putting too much ice in her tea.

Nothing makes sense, and you feel like a ghost. Once you’ve been there, you never really leave Aleppo.

Back in Chicago, it’s my patients who help me stay focused. I had a patient I’ll call Sarah who had a sarcoma of the leg when she was 8. She endured a year of chemotherapy and had a portion of her fibula removed to excise the cancer, followed by radiation. The treatment stunted her leg’s growth and deformed her ankle, but she wanted to be able to run track and play soccer.

On a ski trip to Colorado, she saw people skiing on prosthetics, and that’s what she wanted. When she turned 11, she looked me in the eye and asked me to amputate her left leg. She showed such strength. She reminded me of Ahmad, a Syrian boy who had lost both legs, as well as his mother, when a bomb destroyed their home. He hoped one day to get robotic prostheses so he could walk again. His resilience was inspiring.

Each time I go back to Aleppo, though, conditions are worse. The pockets of life have become more tenuous with each visit. The markets, the children in the streets, the bustle of day-to-day living is replaced with rubble: apocalyptic wastelands of gutted buildings with collapsed roofs, exposed rebar and twisted staircases.

But people still live amid the ruins. You see them hanging laundry from a room on the third floor of a building cut in half. You see kids climbing over a 10-foot mound of rubble on their way home with some bread and water. Life has to go on, and people find ways to cope. They would rather face death at home than suffer in a refugee camp or risk drowning in a sinking boat.

For a surgeon in this setting, triage decisions mean the difference between life and death. A mother pleads with me to attend to her son; his skull is blown open, his brain exposed. He’s gone. There’s nothing we can do.

I move on to a girl with a lacerated artery in her amputated leg. She could bleed to death in minutes, but with pressure and a tourniquet we buy some time. Next to her is another young girl. Her right hand is obliterated: frayed tendons, twisted fingers, crushed bones. Her mother grips my shoulder, begging me to take her daughter to surgery first. But the girl is alive and she can wait.

This can last for hours. I lose all track of time. Eventually, the chaos dissipates. The floors are mopped clean. The dead are wrapped in white shrouds and laid in the street to make room for the next incoming tide of the wounded and dying.

You feel powerless. You can’t stop it. There aren’t enough hands to help, and you can’t save everyone. Should we give all of our blood supplies to save one life? Or ration them to save five who all need some? The choices are impossible, yet we make them.

The Syrian medics and rescue workers in Aleppo have sacrificed everything, some even their lives. They show up to work every day despite all the horrifying brutality. Those of us who go to volunteer cannot stop the bombs, but we can serve in solidarity with Syria’s full-time lifesavers. Who would I be if I could not support them and follow their lead for a few weeks a year?

They are among the most heroic, courageous and selfless people I have ever met — much like the New York firefighters I met on Sept. 11, 2001. A medical student at the time, I squeezed into an ambulance with nurses and medics and we drove toward the smoke and ashes to help. I saw firefighters, paramedics, police officers and citizens rushing to the World Trade Center. That was the side I wanted to be on.

We wrote our names on the back of our scrubs with black markers in case our bodies needed to be identified. I was scared, but I was surrounded by good people doing the right thing.

I had never felt that way again until I went back to Aleppo in August 2013. I had visited Syria several times growing up, and knew Aleppo, but that was my first trip since the conflict started. The overwhelming sadness and dread I felt on Sept. 11, I feel every day in Aleppo.

One night, we treated a child caught in an explosion who had the bone shards of obliterated bystanders embedded in his skin. An airstrike hit his school during a charity event to donate clothes to the poor. The last thing he remembered was seeing his best friend disintegrate in front of him.

The boy’s father saw me and asked who I was, and why I was speaking in a strange language. A nurse explained to him that I was an American doctor. He told me that he had never met an American. He never thought he would. He never believed the day would come when an American doctor — one with Syrian blood but born and raised with the freedoms and luxuries of the United States — would come to Aleppo to help in a time of war.

That gave my work a new dimension of meaning: a palpable connection to alleviate the suffering of a people long abandoned. It lets them know that they’re not alone. It has made me only more grateful for my life in America. It’s also why I go back.