What happens in sepsis, exactly?

What is it?

Sepsis is a life-threatening condition in which the body’s reaction to infection starts to damage its own tissues.

Typical symptoms include fever, increased heart rate and breathing rate, and confusion. In severe cases sepsis can cause things like poor organ function and insufficient blood flow. In septic shock the sepsis has caused a dangerously low blood pressure which doesn’t improve even after the patient has been treated with intravenous fluids to increase the blood volume.

It is estimated that there are about 18 million cases of sepsis around the world a year. The mortality rate of sepsis overall is about 30%: in severe sepsis it is 50% and in septic shock it is 80%.

What causes it?

Sepsis is caused by the body’s reaction to an infection. These infections can be caused by all sorts of pathogens and originate in many parts of the body. Bacteria are the most common pathogens, and the infection most often begins in the lungs.

What happens during it?

In an ideal situation, any invading bacteria are dealt with straight away in the tissue. We have certain immune cells called macrophages sitting around in our tissues, and they start to eat the bacteria. They also produce molecules called cytokines that promote inflammation. This calls more white blood cells to come to the infected area to join the battle, and the blood vessel walls become more permeable to allow the cells to get through to the tissues.

Macrophages kill bacteria through first forming a vesicle around them and engulfing that vesicle, and then making the bacterium-containing vesicle fuse with a dangerous vesicle which the macrophage has created. These dangerous vesicles can contain things like enzymes that start breaking the structure of the bacteria. In an ideal situation the tissue macrophages would kill the bacteria straight away, but sometimes the bacteria can escape and the dangerous vesicles can start damaging the body’s own cells. Inflammation is also useful in the short term, but if there are lots of pathogens and the body can’t deal with them efficiently enough, the inflammation can continue for too long and start to harm the body. This is essentially what happens in sepsis.

Low blood pressure can be a particularly dangerous complication of sepsis. There are muscles in the blood vessel walls that normally keep the blood pressure at appropriate levels, but inflammation can cause these muscles to relax too much and hence lead to lower blood pressure. Inflammation also causes the blood vessel walls to become more permeable to let more white blood cells to the tissues, but this also means that more fluid leaks to the tissues. Blood pressure is what makes blood move around our body, and if it’s too small, the blood doesn’t get quickly enough to where it needs to be. All our organs need the oxygen that blood gives them in order to function, and if the blood pressure is low enough to seriously interfere with normal blood flow, many of our vital organs can stop functioning properly. Our heart and breathing rates probably increase because our body recognizes this lack of oxygen and tries to compensate for it.

In reality sepsis is a very complex condition and not fully understood, but I hope that I managed to piece together a rough yet reasonably accurate account of what actually happens in the body during it.

How can it be treated?

Sepsis is a medical emergency and it should always be treated in a hospital. Treatments vary from case to case, but it’s very common to give antibiotics to get rid of the infection-causing pathogen and to give intravenous fluids to raise the blood pressure to normal levels again. The body needs more oxygen than usual during sepsis, and quite often some extra oxygen is also given to the patient.

While sepsis is a very serious complication, full recovery is likely if it’s recognized and treated quickly.




Sources: https://en.wikipedia.org/wiki/Sepsis, https://en.wikipedia.org/wiki/Septic_shock, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3684427/, http://www.nhs.uk/Conditions/Blood-poisoning/Pages/Treatment.aspx, https://en.wikipedia.org/wiki/Vasodilation


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