From Chapter 6:

Harry was examining the wizarding equivalent of a first-aid kit, the Emergency Healing Pack Plus. There were two self-tightening tourniquets. A Stabilisation Potion, which would slow blood loss and prevent shock. A syringe of what looked like liquid fire, which was supposed to drastically slow circulation in a treated area while maintaining oxygenation of the blood for up to three minutes, if you needed to prevent a poison from spreading through the body. White cloth that could be wrapped over a part of the body to temporarily numb pain. Plus any number of other items that Harry totally failed to comprehend, like the "Dementor Exposure Treatment", which looked and smelled like ordinary chocolate. Or the "Bafflesnaffle Counter", which looked like a small quivering egg and carried a placard showing how to jam it up someone's nostril.

From Chapter 89:

"Fuego!" / "Incendio!" Harry heard, but he wasn't looking, he was reaching for the syringe of glowing orange liquid that was the oxygenating potion, pushing it into Hermione's neck at what Harry hoped was the carotid artery, to keep her brain alive even if her lungs or heart stopped, so long as her brain stayed intact everything else could be fixed, it had to be possible for magic to fix it, it had to be possible for magic to fix it, it had to be possible for magic to fix it, and Harry pushed the plunger of the syringe all the way down, creating a faint glow beneath the pale skin of her neck. Harry then pushed down on her chest, where her heart should be, hard compressions that he hoped was moving the oxygenated blood around to where it could reach her brain, even if her heart might have stopped beating, he hadn't actually thought to check her pulse.

The oxygenation potion also slows circulation. Did Harry accidentally kill Hermione? Would the potion have unintentionally prevented blood flow to her brain by retarding flow in her carotid artery, while unhelpfully oxygenating her neck? It makes sense that a potion designed to prevent the spread of poison would prevent movement of the blood. It's also stated that it works on "a treated area." If it's primarily meant to slow the spread of poisons from bites, the spell's "treated area" might be defined as the volume of flesh a certain distance away from the injection site.

Also, giving CPR to someone when their heart is still beating is definitely not good for them.