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Biology plays rough.
For billions of years, organisms have competed over finite resources for survival.
And sometimes, they resort to hostile takeover.
Infection occurs when disease-causing micro-organisms (pathogens) invade our bodies, multiplying and causing damage.
In an attempt to avoid this, our immune systems are engaged in a never-ending arms race with these pathogens, each continually trying to outsmart the other.
Along the way, we developed all kinds of weapons, like the lymphatic system, memory cells, and antibodies.
But that doesn't stop us from leaning on one of the oldest tricks in the book:
Immunity is expensive.
Rather than personalising a response for every tiny insult, our bodies have an initial, generalised response to deal with percieved threats.
One aspect of this response is inflammation.
Inflammation involves recruitment of immune cells and dilation of nearby blood vessels. Its five features are:
All in all, this is designed to remove pathogens, clear cellular debris, and promote healing.
But sometimes, things get out of hand:
Sepsis occurs when the body's normal immune response spirals out of control.
Rather than the usual, self-limiting process, we see a systemic inflammatory response, leading to massive vasodilation all throughout the body.
This rapidly drops SVR, preload, CO, and thus MAP, leading to a kind of distributive shock known as "septic shock".
But unfortuntately, that's not all.
As part of its inflammatory response, sepsis can also cause body-wide abnormal blood clotting ("sepsis-induced coagulopathy").
Here, the body forms tiny blood clots ("microthrombi") that can impede blood flow, while also consuming platelets that would otherwise be used to prevent harmful bleeding.
The net effect of all this? Reduced delivery of blood to vital organs (including the brain), and increased risk of death.
As you might imagine, this all requires prompt intervention.
And a core pillar of this intervention is pharmacological management.