Sepsis

The title of this post might make one think I’m going to discuss this topic in serious terms. I am very interested in sepsis (severe sepsis and septic shock) since I have some early interests in critical care medicine, but I want to post a brief excerpt from an e-mail on our class mailing list with a response from one of my favorite Infectious Disease physicians/professors to a student’s question on what happens in sepsis:

“With bacteria that are very pathogenic to humans… there is very little local control of the inflammatory response – they get in there (usually in the blood) and multiply like mad before any localizing stuff happens, so inflammatory mediators are spilled all over (systemically), followed by anti-inflammatory ones, and ALL GOES NUTS.”

I usually try to pair photographs and other images to my post topics. This is the best I could do:

allgoesnuts.jpeg

[Caption: ALL GOES NUTS.]

Interestingly, bacteremia and sepsis are not the same, even though the terms are sometimes used interchangeably. Sepsis refers to the body’s (normal) systemic response to an infection, and it precedes bacteremia, the presence of bacteria in the circulatory system (e.g. “bacter-” = bacteria, “-emia” = in the blood). That is, the body’s immune response has to break down in order for bacteremia to occur, often following this sequence:

sepsis -> severe sepsis -> septic shock -> bacteremia

In an ICU setting, an injury or acute disease in one or more parts of the body draws the attentions of the immune system and the body’s repair mechanisms to those areas, leaving the body as a whole in a partially immunocompromised state. Certain life support technologies, such as ventilators with endotracheal tubes, occasionally allow otherwise “normal flora” (bacteria normally found in or on certain parts of the body without any symptoms) to migrate or grow into other parts of the body, such as mouth flora following endotracheal tubes down into the lungs. When this happens, some of the immune system’s signaling molecules that were previously focused on localized problems elsewhere spill out into the blood stream to try and fight off this new infection, but the response may not be sufficient as resources are spread thin. The new infection is unable to be contained locally without a strong immune response. As a result, a variety of both inflammatory (pro-immune response) and anti-inflammatory (attenuating the immune response) molecules are circulating through the body, triggering a much broader, systemic response to the various insults and injuries to the body and the growing infection (much like trying to put out multiple, widespread forest fires with a single fire-fighting plane). One of these seemingling unintended, uncontrolled, systemic responses is (septic) shock, a state in which various parts of the body cannot get the oxygen they need to function (sometimes resulting in death within hours). It is often only after (septic) shock occurs that bacteria start to invade the circulatory system and spread to other parts of the body.

There is still much to be learned and explained about the complicated processes of sepsis and septic shock, especially the observation that it is actually the anti-inflammatory molecules that are found in the greatest amounts in the blood!

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