Sepsis and Infectious Disease

1. Start with what's actually happening in the vessels

An infection gets into the body, and the immune system overreacts to it. That overreaction is sepsis. It's not the bacteria doing the damage directly — it's your own inflammatory response, dysregulated and running too hot.

That response does two things to the blood vessels. It dilates them, so the whole container gets bigger. And it makes the vessel walls leaky, so fluid seeps out of the bloodstream and into the surrounding tissue. Picture a Chinese finger trap. The harder the body pulls against the infection, the tighter and more chaotic the whole system's constriction gets. Every pull only makes it worse. That's the trap sepsis puts the vasculature in — dilation and leak, fed by the very response meant to fight the infection off.

So the container got bigger, and it started leaking. Less blood is circulating where it needs to be, even though total body fluid hasn't gone anywhere. On top of that, the cells lose their ability to pull oxygen out of the blood that does reach them. That's why sepsis is distributive shock with an oxygen-extraction problem. That's why a septic patient can look warm, well-perfused, and normotensive right up until they crash.