It was just after midnight when the call came in. “Fifteen-year old male, single G.S.W.” — gun shot wound — “to the abdomen,” I heard over the loudspeaker. “Stable vitals.”

Earlier that night, we had treated another young man who had been shot in the abdomen. He’d been hit just outside the hospital and walked in, clutching his belly and yelling in pain. The bullet went straight through the left side of his abdomen, puncturing his spleen, before it exited through a small wound in his upper back. In the operating room, surgeons removed his spleen and tied off the bleeding vessels. He went to the I.C.U. in stable condition.

This new patient was also screaming and yelling. He also had a single gunshot wound to his left upper belly. When the paramedics wheeled him in, his heart rate, blood pressure and oxygen levels were normal.

“It’s going to be O.K.,” a nurse said to him. “You’re going to be fine.”

But things were not O.K. Two minutes later, he was gasping for breath. His oxygen level was dropping, as was his blood pressure. When we turned him over, we found an exit wound the size of a small grapefruit.