Septic shock is a syndrome in which a potentially lethal drop in blood pressure occurs as a result of an overwhelming bacterial infection .
Bacteremia —Invasion of the bloodstream by bacteria.
Septic shock is a possible consequence of bacteremia, which is also called sepsis. Bacterial toxins, and the immune system's response to them, can cause a dramatic drop in blood pressure and may result in under-perfusion to various organs. Septic shock can lead to multiple organ failure, including respiratory failure , and may cause rapid death. Toxic shock syndrome is one type of septic shock.
Causes and symptoms
During an infection, certain bacteria can release complex molecules, called endotoxins, that may provoke a dramatic response by the body's immune system . Endotoxins are particularly dangerous; as they become widely dispersed, they cause arteries and the smaller arterioles to dilate. At the same time, the walls of the blood vessels become leaky, allowing fluid to seep into the tissues, lowering intravascular volume (the amount of fluid left in circulation). This combination, of arterial dilation and decreased intravascular volume, causes a dramatic decrease in blood pressure and impaired blood flow to multiple organs. Other changes seen in septic shock are disseminated intravascular coagulation (DIC), which can further impair organ perfusion (blood flow).
Septic shock is seen most often in patients with impaired host defenses (patients who are immunosuppressed), and is often due to nosocomial (hospitalacquired) infections. The immune system is suppressed by drugs used to treat cancer , autoimmune disorders , organ transplants, and diseases of immune deficiency such as AIDS . Malnutrition, chronic drug abuse, and long-term illness also increase the likelihood of succumbing to bacterial infection. Bacteremia is more likely with preexisting infections such as urinary or gastrointestinal tract infections, or skin ulcers. Bacteria may be introduced to the blood stream by surgical procedures, catheters, or intravenous equipment.
Toxic shock syndrome (TSS) is a potentially fatal disorder resulting from infection with Staphylococcus aureus, a toxin-producing strain of a bacteria. When it was first reported about 25 years ago, toxic shock syndrome was associated with menstruation and linked to super-absorbent tampon use. Today, it is recognized that use of super-absorbent tampons does increase the risk of TSS, as does use of a contraceptive sponge or diaphragm. Postpartum patients (women who have just given birth) and patients with wound infections, or recovering from nasal surgery also are at risk for TSS. The illness appears suddenly, with fever , rash, low blood pressure, and episodes of fainting. Survival has improved since the 1980s, approximately 2–5% of patients die from this dis-order. Patients recovering from TSS face increased risk of recurrence. To prevent TSS, menstruating women are advised to avoid use of super-absorbent tampons.
Septic shock is usually preceded by bacteremia, which causes fever, malaise, chills, and nausea. The first sign of shock is often confusion and decreased consciousness. In this beginning stage, the extremities are usually warm. Later, as the blood pressure drops, they may become cool, pale, and cyanotic (bluish). Fever may subside to normal temperatures later on in sepsis.
Other symptoms include:
- rapid heartbeat
- shallow, rapid breathing
- decreased urination
- reddish patches in the skin
Septic shock may progress to cause "adult respiratory distress syndrome," (also called non-cardiogenic pulmonary edema ) in which the pulmonary capillaries become leaky and the lungs fill with fluid. This can lead to respiratory failure. When this occurs the patient can no longer breathe without mechanical ventilation and supplemental oxygen.
Diagnosis of septic shock is made when a patient with a severe infection has hypotension (low blood pressure) for which other causes such as major bleeding, dehydration , or massive myocardial infarction have been excluded. Pulmonary artery pressure may be monitored with a Swan-Ganz catheter, a catheter inserted into the pulmonary artery. Blood, urine, sputum, and cultures from other possible sites of infection determine the type of bacteria responsible for the infection. Arterial blood gases are also monitored to assess changes in respiratory function.
Septic shock is treated initially with a combination of antibiotics and fluid replacement. The antibiotic is chosen based on the bacteria known or suspected to be present. Usually, two or more types of antibiotics are started until the organism is identified. Intravenous fluids replete the intravascular fluid lost by leakage. Impaired coagulation and hemorrhage may be treated with transfusions of plasma, platelets, or red blood cells. Dopamine may be given to increase blood pressure further if necessary.
Respiratory distress is treated with mechanical ventilation and supplemental oxygen, either using a nose-piece or a tube into the trachea through the throat. The mainstay of therapy is to treat the underlying infection that caused the septic shock.
Septic shock is most likely to develop in the hospital, since it frequently results from hospital-acquired infection. Close monitoring and early, aggressive therapy can minimize the likelihood of progression. Nonetheless, death occurs in at least 25% of all cases.
The likelihood of recovery from septic shock depends on many factors, including the degree of immunosuppression of the patient, underlying disease, timeliness of treatment, and type of bacteria responsible. Mortality is highest in the very young and the elderly, those with persistent or recurrent infection, and those with compromised immune systems.
Health care team roles
Generally, care for the septic patient is delivered by hospital-based health care professionals in the hospital ICU (intensive care unit). Physicians, intensive care nurses, and other nursing personnel closely monitor patients' vital signs and administer antibiotics and fluids. Laboratory technologists perform necessary blood tests, and respiratory therapists may provide oxygen to patients in respiratory distress.
The risk of developing septic shock can be minimized through treatment of underlying bacterial infections and prompt attention to signs of bacteremia. In the hospital, scrupulous aseptic technique on the part of medical professionals reduces the risk of introducing bacteria into the bloodstream.
Fauci, Anthony S., ed. Harrison's Principles of Internal Medicine, 14th ed. New York: McGraw-Hill, 1998.
The Washington Manual of Medical Therapeutics, 30th edition. Philadelphia: Lippincott Williams & Wilkins, 2001, pp. 213.
Merck Manual On-line. <http://www.merck.com/pubs/manual/>