A gunshot wound through the chest is clearly a threat to survival, and few might expect the cop on the beat to be able to patch it up.

But a Prince George’s County officer did just that on Friday night, and, according to the county police, he kept the victim breathing and helped save a life.

The county police began training its officers this year in the use of a bag of medical equipment known as a trauma kit, and medical personnel credited Officer Brandon Farley with using his kit to prevent one of the most serious consequences of a chest wound.

The shooting occurred about 8:30 p.m. in the 5300 block of Sheriff Road, police said. After Farley ministered to the victim at the scene, the teenager was rushed to a hospital, police said, where his condition was judged to be critical but stable.

“Medical personnel at the hospital reported that Officer Farley’s quick thinking and timely medical aid stabilized the victim and prevented his lung from collapsing,” the police said.

When Farley reached the scene, which is near Eastern Avenue, he found that the victim had been shot in the back. The bullet had passed through his lung and come out through the front of his chest.

Brandon, according to the police department, immediately recognized the dangerous nature of the wound, and grabbed his trauma kit.

The victim was having trouble breathing, Farley said, the result of air entering his chest through at least one of the bullet holes. The pressure of the air prevents the lung from expanding as part of its natural operation.

Rapid treatment is required to keep the lung from collapsing entirely, impairing the victim’s ability to breathe.

Treatment calls for sealing the wound to keep air from the interior of the chest. The trauma kit contains a dressing suited to the task, Farley said. It is a sticky adhesive dressing, made of gel. Applied to the areas around the bullet holes, it seals the chest, preventing air from entering. It is called an “occlusive dressing”

Using the dressing relieved pressure on the victim’s lungs, and “seemed to allow him to breathe better and avoid a collapsed lung,” Farley said.

It appeared to be a level of care that might not be expected from a police officer sent to the scene of the shooting.

However, police said county officers have used the trauma kits to save lives several times already this year.

Police said they thought that the shooting may have followed an argument.

They said initial information indicated that the victim was shot by a black man with a medium build. Police sid he may have been wearing a a blue Helly Hansen jacket, dark pants and black boots. He fled in a dark colored four-door car, they said.