Septic shock - Causes of septic shock

Septic shock can be caused by an infection in any part of the body that is left untreated.

The infection will first cause a response from the body known as sepsis.

Bacterial infections are the most common cause of sepsis. Fungi, such as candida, and viruses can also sometimes lead to sepsis, although this is rare.

Bacterial infections occur if harmful bacteria enter the blood through the skin – for example, when an intravenous drip or catheter has been inserted. Sepsis can also happen after an infection in one of the organs – for example, a urinary tract infection or lung infection.

Read more information about the causes of sepsis.

How septic shock develops

If left untreated, the toxins produced by bacteria can severely damage the body’s cells. They attack the walls of the small blood vessels, causing them to leak fluid from the blood into the surrounding tissues. It can also decrease the heart's ability to pump blood to the organs. This is called acute circulatory failure, or shock. It significantly lowers your blood pressure.

The fall in blood pressure means the heart cannot supply the body’s vital organs with oxygen-rich blood. Without an oxygen-rich blood supply, the brain, heart, kidneys and liver cannot function properly.

The fall in blood pressure, which does not respond to treatment with fluids, is what distinguishes septic shock from severe sepsis.

Risk factors

Certain groups of people are more at risk of developing septic shock. This is because their immune systems are weaker, which reduces their ability to fight serious infections.

People who are particularly at risk of developing septic shock include:

• newborn babies
• elderly people
• pregnant women
• people with long-term health conditions such as diabetes, cirrhosis or kidney failure
• people with lowered immune systems, such as people with HIV or AIDS or people receiving chemotherapy