septic shock

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Septic Shock



Septic shock is a potentially lethal drop in blood pressure due to the presence of bacteria in the blood.


Septic shock is a possible consequence of bacteremia, or bacteria in the bloodstream. Bacterial toxins, and the immune system response to them, cause a dramatic drop in blood pressure, preventing the delivery of blood to the 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 types of bacteria can produce and release complex molecules, called endotoxins, that may provoke a dramatic response by the body's immune system. Released in the bloodstream, endotoxins are particularly dangerous, because they become widely dispersed and affect the blood vessels themselves. Arteries and the smaller arterioles open wider, increasing the total volume of the circulatory system. At the same time, the walls of the blood vessels become leaky, allowing fluid to seep out into the tissues, lowering the amount of fluid left in circulation. This combination of increased system volume and decreased fluid causes a dramatic decrease in blood pressure and reduces the blood flow to the organs. Other changes brought on by immune response may cause coagulation of the blood in the extremities, which can further decrease circulation through the organs.
Septic shock is seen most often in patients with suppressed immune systems, and is usually due to bacteria acquired during treatment at the hospital. 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 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 most often occurs in menstruating women using highly absorbent tampons. Left in place longer than other types, these tampons provide the breeding ground for Staphylococcus bacteria, which may then enter the bloodstream through small tears in the vaginal lining. The incidence of toxic shock syndrome has declined markedly since this type of tampon was withdrawn from the market.


Septic shock is usually preceded by bacteremia, which is marked by 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, they become cool, pale, and bluish. Fever may give way to lower than 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," in which fluid collects in the lungs, and breathing becomes very shallow and labored. This condition may lead to ventilatory collapse, in which the patient can no longer breathe adequately without assistance.


Diagnosis of septic shock is made by measuring blood pressure, heart rate, and respiration rate, as well as by a consideration of possible sources of infection. Blood pressure may be monitored with a catheter device inserted into the pulmonary artery supplying the lungs (Swan-Ganz catheter). Blood cultures are done to determine the type of bacteria responsible. The levels of oxygen, carbon dioxide, and acidity in the blood 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 present, although two or more types of antibiotics may be used initially until the organism is identified. Intravenous fluids, either blood or protein solutions, replace the fluid lost by leakage. Coagulation and hemorrhage may be treated with transfusions of plasma or platelets. Dopamine may be given to increase blood pressure further if necessary.
Respiratory distress is treated with mechanical ventilation and supplemental oxygen, either using a nosepiece or a tube into the trachea through the throat.
Identification and treatment of the primary infection site is important to prevent ongoing proliferation of bacteria.


Septic shock is most likely to develop in the hospital, since it follows infections which are likely to be the objects of treatment. Because of this, careful 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 may factors, including the degree of immunosuppression of the patient, underlying disease, promptness 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.


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 lowers the risk of introducing bacteria into the bloodstream.



The Merck Page. April 13, 1998.

Key terms

Bacteremia — Invasion of the bloodstream by bacteria.


1. a sudden disturbance of mental equilibrium.
2. a condition of acute peripheral circulatory failure due to derangement of circulatory control or loss of circulating fluid. It is marked by hypotension and coldness of the skin, and often by tachycardia and anxiety. Untreated shock can be fatal. Called also circulatory collapse.

Mechanisms of Circulatory Shock. The essentials of shock are easier to understand if the circulatory system is thought of as a four-part mechanical device made up of a pump (the heart), a complex system of flexible tubes (the blood vessels), a circulating fluid (the blood), and a fine regulating system or “computer” (the nervous system) designed to control fluid flow and pressure. The diameter of the blood vessels is controlled by impulses from the nervous system which cause the muscular walls to contract. The nervous system also affects the rapidity and strength of the heartbeat, and thereby the blood pressure as well.

Shock, which is associated with a dangerously low blood pressure, can be produced by factors that attack the strength of the heart as a pump, decrease the volume of the blood in the system, or permit the blood vessels to increase in diameter.
Types of Circulatory Shock. There are five main types: Hypovolemic (low-volume) shock occurs whenever there is insufficient blood to fill the circulatory system. Neurogenic shock is due to disorders of the nervous system. Anaphylactic (allergic) shock and septic shock are both due to reactions that impair the muscular functioning of the blood vessels. And cardiogenic shock is caused by impaired function of the heart.
Hypovolemic (Low-Volume) Shock. This is a common type that happens when blood or plasma is lost in such quantities that the remaining blood cannot fill the circulatory system despite constriction of the blood vessels. The blood loss may be external, as when a vessel is severed by an injury, or the blood may be “lost” into spaces inside the body where it is no longer accessible to the circulatory system, as in severe gastrointestinal bleeding from ulcers, fractures of large bones with hemorrhage into surrounding tissues, or major burns that attract large quantities of blood fluids to the burn site outside blood vessels and capillaries. The treatment of hypovolemic shock requires replacement of the lost volume.
Neurogenic Shock. This type, often accompanied by fainting, may be brought on by severe pain, fright, unpleasant sights, or other strong stimuli that overwhelm the usual regulatory capacity of the nervous system. The diameter of the blood vessels increases, the heart slows, and the blood pressure falls to the point where the supply of oxygen carried by the blood to the brain is insufficient, which can bring on fainting. Placing the head lower than the body is usually sufficient to relieve this form of shock.
Anaphylactic (Allergic) Shock. This type (see also anaphylaxis) is a rare phenomenon that occurs when a person receives an injection of a foreign protein but is highly sensitive to it. The blood vessels and other tissues are affected directly by the allergic reaction. Within a few minutes, the blood pressure falls and severe dyspnea develops. The sudden deaths that in rare cases follow bee stings or injection of certain medicines are due to anaphylactic reactions.
Septic Shock. This type, resulting from bacterial infection, is being recognized with increasing frequency. Certain organisms contain a toxin that seems to act on the blood vessels when it is released into the bloodstream. The blood eventually pools within parts of the circulatory system that expand easily, causing the blood pressure to drop sharply. Gram-negative shock is a form of septic shock due to infection with gram-negative bacteria.
Cardiogenic Shock. This type may be caused by conditions that interfere with the function of the heart as a pump, such as severe myocardial infarction, severe heart failure, and certain disorders of rate and rhythm.
Pathogenesis of shock. (ARDS = adult respiratory distress syndrome, GI = gastrointestinal, IL = interleukin, TNF = tumor necrosis factor.) From Damjanov, 2000.
anaphylactic shock see anaphylactic shock.
cardiogenic shock shock resulting from primary failure of the heart in its pumping function, as in myocardial infarction, severe cardiomyopathy, or mechanical obstruction or compression of the heart; clinical characteristics are similar to those of hypovolemic shock.
colloidoclastic shock colloidoclasia.
cultural shock feelings of helplessness and discomfort experienced by an outsider attempting to comprehend or effectively adapt to a different cultural group or unfamiliar cultural context.
electric shock see electric shock.
hypovolemic shock shock resulting from insufficient blood volume for the maintenance of adequate cardiac output, blood pressure, and tissue perfusion. Without modification the term refers to absolute hypovolemic shock caused by acute hemorrhage or excessive fluid loss. Relative hypovolemic shock refers to a situation in which the blood volume is normal but insufficient because of widespread vasodilation as in neurogenic shock or septic shock. Clinical characteristics include hypotension; hyperventilation; cold, clammy, cyanotic skin; a weak and rapid pulse; oliguria; and mental confusion, combativeness, or anxiety.
insulin shock a hypoglycemic reaction to overdosage of insulin, a skipped meal, or strenuous exercise in an insulin-dependent diabetic, with tremor, dizziness, cool moist skin, hunger, and tachycardia; if untreated it may progress to coma and convulsions.
respirator shock circulatory shock due to interference with the flow of blood through the great vessels and chambers of the heart, causing pooling of blood in the veins and the abdominal organs and a resultant vascular collapse. The condition sometimes occurs as a result of increased intrathoracic pressure in patients who are being maintained on a mechanical ventilator.
septic shock shock associated with overwhelming infection, usually by gram-negative bacteria, although it may be produced by other bacteria, viruses, fungi, and protozoa. It is thought to result from the action of endotoxins or other products of the infectious agent on the vascular system causing large volumes of blood to be sequestered in the capillaries and veins; activation of the complement and kinin systems and the release of histamine, cytokines, prostaglandins, and other mediators may be involved. Clinical characteristics include initial chills and fever, warm flushed skin, increased cardiac output, and a lesser degree of hypotension than with hypovolemic shock; if therapy is ineffective, it may progress to the clinical picture associated with hypovolemic shock.
shell shock old term for posttraumatic stress disorder.
spinal shock the loss of spinal reflexes after injury of the spinal cord that appears in the muscles innervated by the cord segments situated below the site of the lesion.

sep·tic shock

1. shock associated with infection that has released large enough quantities of toxins or vasoactive substances including cytokines, to be associated with hypotension;
2. shock associated with septicemia caused by gram-negative bacteria.

septic shock

A condition of physiologic shock caused by an overwhelming infection, especially sepsis or septicemia.

septic shock

a form of shock that occurs in septicemia when endotoxins or exotoxins are released from certain bacteria in the bloodstream, occasionally caused by the presence of fungi or viruses in the blood. These toxins cause vasodilation, resulting in a dramatic fall in blood pressure. Fever, tachycardia, increased respiration rate, and confusion or coma also may occur. Septic shock is usually preceded by signs of severe infection, often of the genitourinary or GI system. The causative bacterium is most frequently gram-negative. Antibiotics, vasopressors, and IV fluids and volume expanders are usually given. In some cases, treatment with monoclonal antibodies may be considered. Kinds of septic shock include toxic shock syndrome and bacteremic shock. Compare hypovolemic shock. See also shock.

septic shock

Bacteremic shock Infectious disease A condition identical to the sepsis syndrome with an added component of hypotension–systolic BP < 90 mm Hg or loss in the baseline systolic BP of > 40 mm Hg; SS has been formally defined by clinical parameters as 'Sepsis-induced hypotension despite fluid resuscitation plus hypoperfusion abnormalities…', which include lactic acidosis, oliguria, or an acute alteration in mental status; SS is end-stage of a continuum of a biologic inflammatory response to infection Etiology Gram-negative bacilli–eg, E coli, Klebsiella spp, gram-positive cocci–eg, Staphylococcus spp; viruses, fungi rarely cause SS Epidemiology SS kills 100k to 175k people/yr–US, 13th major cause of death in US Risk factors Underlying disease–DM; hematologic CA; GI, GU, hepatobiliary disease, recent infection, prolonged antibiotics, recent surgery Clinical Either reflect response to infection–ie, tachycardia, tachypnea, changes in temperature, leukocytosis, or the organ system(s) involved–eg, cardiovascular, hematologic, hepatic, renal, pulmonary; SS is severe if there is hypoperfusion, lactic acidosis, hypotension, or altered mental status Mediators Bacterial endotoxin evokes a vehement response by the complement system, kinin system, and plasma phospholipases and release of various cytokines–eg, TNF-a, IL-1, IL-6, β-endophins, PAF, PGs, leukotrienes. See Sepsis, Sepsis syndrome, Severe sepsis, SIRS.

sep·tic shock

(sep'tik shok)
1. Condition associated with sepsis and usually associated with abdominal and pelvic infection complicating trauma or operations.
2. Condition associated with septicemia caused by gram-negative bacteria.

Septic shock

A dangerous condition caused by damage to immune cells, the endothelium of blood vessels and the malfunction of most of the organs of the body by the uncontrolled production of potent CYTOKINES mainly by bacterial pathogens. These include tumour necrosis factor and interleukin-1 which are produced as a response to the toxins of bacteria in the course of SEPTICAEMIA. Small blood vessels become leaky and so much fluid is lost into the tissue spaces that the normal circulation cannot be maintained and the blood pressure drops. This is called shock and it is similar in effect to shock from other causes such as severe blood loss or severe burns. Urgent treatment with antibiotics, transfusion and organ support is necessary to save life.

sep·tic shock

(sep'tik shok)
1. Shock associated with infection that has released large enough quantities of toxins or vasoactive substances including cytokines, to be associated with hypotension.
2. Shock associated with septicemia caused by gram-negative bacteria.


pertaining to sepsis.

septic fever
is fever associated with infection either as local abscess or cellulitis or as a septicemia or bacteremia. The infective agent may be a bacteria, virus, fungus, protozoa or even algae.
septic mastitis
mastitis characterized by the presence of bacteria in the milk.
septic shock
see toxemic shock.


a condition of acute peripheral circulatory failure due to derangement of circulatory control or loss of circulating fluid. It is marked by hypotension, coldness of the skin and tachycardia.

allergic shock
see anaphylactic shock.
shock bodies
hyaline globules composed of fibrin degradation products which act as microthrombi and cause hemorrhage and necrosis.
burn shock
the loss and redistribution of fluid, electrolytes and plasma protein, increased blood viscosity and increased peripheral resistance that follow a severe burn contribute to shock.
cardiogenic shock
classically associated with acute myocardial infarction in humans; in animals may be caused by intrinsic congestive heart failure, cardiac depression caused by anesthetic overdosage or other drugs with negative inotropism, rarely, thromboembolism.
colloidoclastic shock
shock due to breakdown of the physical equilibrium of the body colloids. Thought to cause anaphylactic shock due to the absorption of the colloids into the bloodstream.
distributive shock
see vasogenic shock (below).
electric shock
see electrical injuries.
electroplectic shock
electric shock. See also electrical stunning.
endotoxic shock
caused by endotoxins, especially Escherichia coli. See also toxemic shock.
shock gut
animals in shock develop changes in the gut including congestion and hemorrhage into the lumen.
hypovolemic shock
shock due to reduced blood volume as a result of water deprivation, fluid loss due to diarrhea, vomiting, extensive burns, intestinal obstruction, whole blood loss.
insulin shock
a condition of circulatory insufficiency resulting from overdosage with insulin, which causes too sudden reduction of blood sugar. It is marked by tremor, weakness, convulsions and collapse.
irreversible shock
shock which has reached the stage where irreparable damage has been done to tissues, e.g. liver, kidneys and treatment will not salvage the patient although it might prolong life for a long time.
shock lung
animals in shock due to massive burns, septicemia, disseminated intravascular coagulation (DIC), acute viral or bacterial pneumonias or trauma develop an acute respiratory distress syndrome. The pulmonary lesion is a nonspecific acute or subacute interstitial pneumonia.
nervous shock
a temporary cessation of function in nervous tissue caused by an acute insult such as trauma without the part having been directly or detectably damaged. The loss of function is only temporary, usually for a few minutes but it may last for several hours. There may be residual signs due to direct damage when the shock passes. Stunning by a lightning stroke is an example.
shock organs
those organs, specific to each animal species, which respond to allergens circulating in the blood.
septic shock
see toxemic shock.
spinal shock
flaccid paralysis up and down the body from the site of the spinal cord lesion. Accompanied by a fall in skin temperature, vasodilatation and sweating. Signs disappear within an hour or two. There may be residual signs due to physical injury to tissue.
toxic shock
see toxemic shock.
vasogenic shock, vasculogenic shock
shock exists because of the severe reduction in effective circulating blood volume caused by sequestration of blood and other fluids in the vascular system and their withdrawal from the circulating blood. Is the classical shock of traumatic injury, burns, uterine prolapse, extensive surgery.