Sepsis is the name given to a severe and damaging systemic inflammatory response caused by an infection. The infection may begin at one site of the body and then spread to the blood and possibly to other sites. While the terms bacteraemia and fungaemiarefer to the detectable presence of bacteria or fungi in the bloodstream, sepsis refers to the body's overwhelming response to the infection, which leads to organ dysfunction. (For more on this, see the article on Blood Culture.) The term septicaemia was historically used to describe sepsis with evidence of bacteraemia, but is no longer considered to accurately describe the processes involved.
Sepsis is a serious condition that can progress from sepsis to severe sepsis and then to septic shock with the failure of one or more organs (multiorgan failure, MOF). Successful treatment requires intensive care unit (ICU) support. Although sepsis commonly occurs and is identified in hospitalised patients, it can also develop in non-hospitalised patients who may then present to the hospital accident and emergency (A&E) department. It is more prevalent in newborns and infants and in the elderly but can affect patients of any age. Patients at risk of sepsis include those with trauma, including after major surgery, the presence of invasive medical devices such as catheters, chronic illnesses, and immunocompromised patients.
Sepsis is a major health problem with severe associated morbidity and mortality rates in the range of 25-50%. Comparable figures have been reported for other parts of the world, including the United States and South America.
Normally a person's immune system targets specific threats and limits the response to the area that is infected. With sepsis, a generalised inflammatory response is initiated by the body. This can cause a significant rise or fall in body temperature, increased heart and respiration rates, and a decrease in blood pressure. If not treated successfully, as noted above, sepsis can progress to severe sepsis and then to septic shock. As the condition progresses to severe sepsis, the amount of oxygen that is carried to tissues and organs decreases, blood clots can form in the capillaries, and fluids can leak from the blood into tissues. This last can cause fluid build-up in the lungs, thereby reducing respiratory function. Overall the body's acid-base balance becomes disrupted, circulation is impaired, waste products begin to accumulate, tissues are damaged, and organs such as the lungs, kidneys, and liver begin to fail. With the last stage of sepsis, septic shock, there may be MOF and low blood pressure that is resistant to treatment.