Septic shock is a type of severe sepsis. This is caused by an infection. Your body responds to the infection with widespread inflammation, which causes the symptoms of sepsis.
Bacterial infection
Sepsis is often caused by a bacterial infection. Fungi, such as candida, and viruses can also sometimes lead to sepsis, although this is rare.
Bacterial infections that cause sepsis often develop while a person is in hospital. Infections that most commonly cause sepsis originate in the:
- lungs – infections affecting your lungs (lower respiratory tract infections), such as pneumonia or bronchitis, may be the cause of septic shock in a quarter of people
- urinary tract (the tubes that carry urine from the kidneys to the outside of the body) – urinary tract infections may be the cause of septic shock in a quarter of people.
- digestive system
- reproductive system
How the infection develops
Bacterial infections occur if harmful bacteria enter the blood through a cut in the skin. Infections can also develop in your body’s organs.
If you are healthy, your immune system (the body’s natural defence system) will kill any bacteria that get into your blood. However, if your immune system is lowered or not working properly, it may become overloaded and unable to fight off infection.
If your immune system fails in this way, the bacteria in your blood will multiply, releasing poisonous chemicals (toxins) into your bloodstream. If this happens, the symptoms of sepsis may develop.
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. 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.
Other conditions caused by sepsis
As well as septic shock, sepsis can also lead to several other serious, life-threatening health conditions, which may then lead to septic shock. These include:
- the lungs not being able to provide oxygen to the rest of the body (acute respiratory distress syndrome)
- proteins that control blood clotting becoming abnormally active (disseminated intravascular coagulation)
- a severe infection of the bloodstream called meningococcemia
- adrenal gland failure due to bleeding into the adrenal gland as a result of severe infection (Waterhouse-Friderichsen syndrome) – the adrenal glands are located above the kidneys, inside the back of the abdominal wall
People who are at risk
People who are particularly at risk of developing sepsis and septic shock include:
- newborn babies
- elderly people
- pregnant women
- people with long-term health conditions
- people with lowered immune systems, such as people with HIV or AIDS or people receiving chemotherapy
These groups are most at risk because their immune systems are weaker. This reduces their ability to fight serious infections, increasing the risk of sepsis.
Risk factors
Health conditions that increase the risk of sepsis and septic shock include:
- diabetes
- cirrhosis of the liver
- HIV or AIDS
- long-term kidney failure
- conditions that affect your heart and lungs
- some types of cancer in the bone marrow and white blood cells (leukaemia)
Other potential risk factors for sepsis and septic shock are:
- using medical devices that are inserted into the body, such as catheters, which may introduce bacteria to the body
- having an artificial joint or heart valve fitted
- major surgery, such as bowel surgery, which increases the risk of bacteria entering the body
- major injuries, such as burns covering a large part of your body
- being in hospital for a long time
- injecting recreational drugs, as syringes that are not sterile can introduce bacteria to your bloodstream
Acute:Acute means occurring suddenly or over a short period of time.
Bacteria:Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.
Blood:Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Heart:The heart is a muscular organ that pumps blood around the body.
Immune:The immune system is the body’s defence system, which helps protect it from disease, bacteria and viruses.
Liver:The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy.
Lungs:Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.
Shock:Shock is a short-term state of body weakness that usually happens after an accident or injury, caused when there is an insufficient supply of oxygen.
Tissues:Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.
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Causes of septic shock
