Merck Manual

Please confirm that you are a health care professional

honeypot link

Sepsis and Septic Shock


Joseph D Forrester

, MD, MSc, Stanford University

Reviewed/Revised Mar 2023
Topic Resources

Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure of multiple organs, including the lungs, kidneys, and liver, can occur. Common causes in immunocompetent patients include many different species of gram-positive and gram-negative bacteria. Immunocompromised patients may have uncommon bacterial or fungal species as a cause. Signs include fever, hypotension, oliguria, and confusion. Diagnosis is primarily clinical combined with culture results showing infection; early recognition and treatment is critical. Treatment is aggressive fluid resuscitation, antibiotics, surgical excision of infected or necrotic tissue and drainage of pus, and supportive care.

Sepsis represents a spectrum of disease with mortality risk ranging from moderate (eg, 10%) to substantial (eg, > 40%) depending on various pathogen and host factors along with the timeliness of recognition and provision of appropriate treatment.

Septic shock is a subset of sepsis with significantly increased mortality due to severe abnormalities of circulation and/or cellular metabolism. Septic shock involves persistent hypotension (defined as the need for vasopressors to maintain mean arterial pressure 65 mm Hg, and a serum lactate level > 18 mg/dL [2 mmol/L] despite adequate volume resuscitation [ 1 General reference Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more ]).

The concept of the systemic inflammatory response syndrome (SIRS), defined by certain abnormalities of vital signs and laboratory results, has long been used to identify early sepsis. However, SIRS criteria have been found to lack sensitivity and specificity for increased mortality risk, which is the main consideration for using such a conceptual model. The lack of specificity may be because the SIRS response is often adaptive rather than pathologic.

General reference

Etiology of Sepsis and Septic Shock

Most cases of septic shock are caused by hospital-acquired gram-negative bacilli or gram-positive cocci and often occur in immunocompromised patients and patients with chronic and debilitating diseases. Rarely, it is caused by Candida or other fungi. A postoperative infection should be suspected as the cause of septic shock in patients who have recently had surgery. A unique, uncommon form of shock caused by staphylococcal and streptococcal toxins is called toxic shock syndrome Toxic Shock Syndrome (TSS) Toxic shock syndrome is caused by staphylococcal or streptococcal exotoxins. Manifestations include high fever, hypotension, diffuse erythematous rash, and multiple organ dysfunction, which... read more Toxic Shock Syndrome (TSS) .

Common causative sites of infection include the lungs and the urinary, biliary, and gastrointestinal tracts.

Pathophysiology of Sepsis and Septic Shock

The pathogenesis of septic shock is not completely understood. An inflammatory stimulus (eg, a bacterial toxin) triggers production of pro-inflammatory mediators, including tumor necrosis factor (TNF) and interleukin (IL)-1. These cytokines cause neutrophil–endothelial cell adhesion, activate the clotting mechanism, and generate microthrombi. They also release numerous other mediators, including leukotrienes, lipoxygenase, histamine, bradykinin, serotonin, and IL-2. They are opposed by anti-inflammatory mediators, such as IL-4 and IL-10, resulting in a negative feedback mechanism.

Initially, arteries and arterioles dilate, decreasing peripheral arterial resistance; cardiac output typically increases. This stage has been referred to as warm shock. Later, cardiac output may decrease, blood pressure falls (with or without an increase in peripheral resistance), and typical features of hypoperfusion appear.

Even in the stage of increased cardiac output, vasoactive mediators cause blood flow to bypass capillary exchange vessels (a distributive defect). Poor capillary flow resulting from this shunting, along with capillary obstruction by microthrombi, decreases delivery of oxygen and impairs removal of carbon dioxide and waste products. Decreased perfusion causes dysfunction and sometimes failure of one or more organs, including the kidneys, lungs, liver, brain, and heart.

Coagulopathy may develop because of intravascular coagulation with consumption of major clotting factors, excessive fibrinolysis in reaction thereto, and more often a combination of both.

Symptoms and Signs of Sepsis and Septic Shock

Symptoms and signs of sepsis can be subtle and often easily mistaken for manifestations of other disorders (eg, primary cardiac dysfunction, pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more Pulmonary Embolism (PE) , delirium Delirium Delirium is an acute, transient, usually reversible, fluctuating disturbance in attention, cognition, and consciousness level. Causes include almost any disorder or drug. Diagnosis is clinical... read more ), especially in postoperative patients. With sepsis, patients typically have fever, tachycardia, diaphoresis, and tachypnea; blood pressure remains normal. Other signs of the causative infection may be present. As sepsis worsens or septic shock develops, an early sign, particularly in older people or the very young, may be confusion or decreased alertness. Blood pressure decreases, yet the skin is paradoxically warm. Later, extremities become cool and pale, with peripheral cyanosis and mottling. Organ dysfunction causes additional symptoms and signs specific to the organ involved (eg, oliguria, dyspnea).

Diagnosis of Sepsis and Septic Shock

  • Clinical manifestations

  • Blood pressure (BP), heart rate, and oxygen monitoring

  • Complete blood count (CBC) with differential, electrolyte panel and creatinine, lactate

  • Invasive central venous pressure (CVP), PaO2, and central venous oxygen saturation (ScvO2) readings

  • Cultures of blood, urine, and other potential sites of infection, including wounds in surgical patients

Sepsis is suspected when a patient with a known infection develops systemic signs of inflammation or organ dysfunction. Similarly, a patient with otherwise unexplained signs of systemic inflammation should be evaluated for infection by history, physical examination, and tests, including urinalysis and urine culture (particularly in patients who have indwelling catheters), blood cultures, and cultures of other suspect body fluids. In patients with a suspected surgical or occult cause of sepsis, ultrasonography (eg, ), CT, or MRI may be required, depending on the suspected source. Blood levels of C-reactive protein and procalcitonin are often elevated in severe sepsis and may facilitate diagnosis, but they are not specific. Ultimately, the diagnosis is clinical.

Other causes of shock (eg, hypovolemia, myocardial infarction Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and/or diaphoresis... read more Acute Myocardial Infarction (MI) [MI]) should be ruled out via history, physical examination, ECG, and serum cardiac markers as clinically indicated. Even in the absence of MI, hypoperfusion caused by sepsis may result in ECG findings of cardiac ischemia including nonspecific ST-T wave abnormalities, T-wave inversions, and supraventricular and ventricular arrhythmias.

It is important to detect organ dysfunction as early as possible. A number of scoring systems have been devised, but the sequential organ failure assessment score (SOFA score) and the quick SOFA score (qSOFA) have been validated with respect to mortality risk and are relatively simple to use. The qSOFA score is based on the blood pressure, respiratory rate, and the and does not require waiting for lab results. For patients with a suspected infection who are not in the intensive care unit (ICU), the qSOFA score is a better predictor of inpatient mortality than the systemic inflammatory response syndrome (SIRS) and SOFA score. For patients with a suspected infection who are in the ICU, the SOFA score is a better predictor of in-patient mortality than the systemic inflammatory response syndrome (SIRS) and qSOFA score (1 Diagnosis reference Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more ).

Patients with 2 of the following criteria meet criteria for SIRS and should have further clinical investigation:

  • Temperature > 38° C (100.4° F) or < 36° C (96.8° F)

  • Heart rate > 90 beats per minute

  • Respiratory rate > 20 breaths per minute or PaCO2 < 32 mm Hg

  • White blood cell count > 12,000/mcL (12 × 109/L), < 4,000/mcL (4 × 109/L) or > 10% immature (band) forms

Patients with 2 of the following qSOFA criteria should have further clinical and laboratory investigation:

  • Respiratory rate 22 breaths per minute

  • Altered mentation

  • Systolic blood pressure 100 mm Hg

The SOFA score is somewhat more robust in the ICU setting, but requires laboratory testing (see table ).


CBC, arterial blood gases (ABGs), chest x-ray, serum electrolytes, BUN (blood urea nitrogen), creatinine, PCO2, and liver function are monitored. Serum lactate levels, central venous oxygen saturation (ScvO2), or both can be done to help guide treatment. White blood cell (WBC) count may be decreased (< 4,000/mcL [< 4 × 109/L]) or increased (> 15,000/mcL [> 15 × 109/L]), and polymorphonuclear leukocytes may be as low as 20%. During the course of sepsis, the WBC count may increase or decrease, depending on the severity of sepsis or shock, the patient's immunologic status, and the etiology of the infection. Concurrent corticosteroid use may elevate WBC count and thus mask WBC changes due to trends in the illness.

Hyperventilation with respiratory alkalosis Respiratory Alkalosis Respiratory alkalosis is a primary decrease in carbon dioxide partial pressure (Pco2) with or without compensatory decrease in bicarbonate (HCO3); pH may be high or near normal.... read more (low PaCO2 and increased arterial pH) occurs early, in part as compensation for lactic acidemia. Serum bicarbonate is usually low, and serum and blood lactate levels increase. As shock progresses, metabolic acidosis worsens, and blood pH decreases. Early hypoxemic respiratory failure Acute Hypoxemic Respiratory Failure (AHRF, ARDS) Acute hypoxemic respiratory failure is defined as severe hypoxemia (PaO2 (See also Overview of Mechanical Ventilation.) Airspace filling in acute hypoxemic respiratory failure (AHRF) may result... read more Acute Hypoxemic Respiratory Failure (AHRF, ARDS) leads to a decreased PaO2:FIO2 ratio and sometimes overt hypoxemia with PaO2 < 70 mm Hg. Diffuse infiltrates may appear on the chest x-ray due to acute respiratory distress syndrome ARDS Acute hypoxemic respiratory failure is defined as severe hypoxemia (PaO2 (See also Overview of Mechanical Ventilation.) Airspace filling in acute hypoxemic respiratory failure (AHRF) may result... read more ARDS (ARDS). BUN and creatinine usually increase progressively as a result of renal insufficiency. Bilirubin and transaminases may rise, although overt hepatic failure is uncommon in patients with normal baseline liver function.

Hemodynamic measurements with a central venous or pulmonary artery catheter Procedure Some monitoring of critical care patients depends on direct observation and physical examination and is intermittent, with the frequency depending on the patient’s illness. Other monitoring... read more Procedure can be used when the specific type of shock is unclear or when large fluid volumes (eg, > 4 to 5 L balanced crystalloid within 6 to 8 hours) are needed.

Bedside echocardiography in the ICU is a practical and noninvasive alternative method of hemodynamic monitoring. In septic shock, cardiac output is increased and peripheral vascular resistance is decreased, whereas in other forms of shock Etiology and Classification Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more , cardiac output is typically decreased and peripheral resistance is increased.

Neither CVP nor pulmonary artery occlusive pressure (PAOP) is likely to be abnormal in septic shock, unlike in hypovolemic, obstructive, or cardiogenic shock.

Many patients with severe sepsis develop relative adrenal insufficiency Secondary Adrenal Insufficiency Secondary adrenal insufficiency is adrenal hypofunction due to a lack of adrenocorticotropic hormone (ACTH). Symptoms are the same as for Addison disease and include fatigue, weakness, weight... read more (ie, normal or slightly elevated baseline cortisol levels that do not increase significantly in response to further stress or exogenous adrenocorticotropic hormone [ACTH]). Adrenal function may be tested by measuring serum cortisol at 8 AM; a level < 5 mcg/dL (< 138 nmol/L) is inadequate. Alternatively, cortisol can be measured before and after injection of 250 mcg of synthetic ACTH; a rise of < 9 mcg/dL (< 248 nmol/L) is considered insufficient.

Rapid Ultrasound for Shock and Hypotension (RUSH) Examination

Diagnosis reference

  • 1. Seymour CW, Liu VX, Iwashyna TJ, et al: Assessment of clinical criteria for sepsis: For the third international consensus definitions for sepsis and septic shock (sepsis-3). JAMA 215(8):762–774, 2016. doi: 10.1001/jama.2016.0288

Treatment of Sepsis and Septic Shock

  • Perfusion restored with IV fluids and sometimes vasopressors

  • Oxygen support

  • Broad-spectrum antibiotics

  • Source control

  • Sometimes other supportive measures (eg, corticosteroids, insulin)

Patients with septic shock should be treated in an ICU. The following should be monitored frequently (as often as hourly):

  • Volume status using central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), serial ultrasound and/or central venous oxygenation saturation (ScvO2)

  • Arterial blood gases (ABGs)

  • Blood glucose, lactate, and electrolyte levels

  • Renal function

Arterial oxygen saturation should be measured continuously via pulse oximetry. Urine output, a good indicator of renal perfusion, should be measured (in general, indwelling urinary catheters should be avoided unless they are essential). The onset of oliguria (eg, < about 0.5 mL/kg/hour) or anuria, or rising creatinine may signal impending renal failure.

Following evidence-based guidelines and formal protocols for timely diagnosis and treatment of sepsis has been shown to decrease mortality and length of stay in the hospital (1 Treatment references Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more ).

Perfusion restoration

IV fluids are the first method used to restore perfusion. Balanced isotonic crystalloid is preferred. Some clinicians add albumin to the initial fluid bolus in patients with severe sepsis or septic shock; albumin is more expensive than crystalloid but is generally a safe complement to crystalloid. Starch-based fluids (eg, hydroxyethyl starch) are associated with increased mortality and should not be used.

Initially, 1 L of crystalloid is given rapidly. Most patients require a minimum of 30 mL/kg in the first 4 to 6 hours. However, the goal of therapy is not to administer a specific volume of fluid but to achieve tissue reperfusion without causing pulmonary edema due to fluid overload.

Estimates of successful reperfusion include ScvO2 and lactate clearance (ie, percent change in serum lactate levels over 6 to 8 hours). Target ScvO2 is 70%. Lactate clearance target is 10 to 20%. Risk of pulmonary edema can be controlled by optimizing preload; fluids should be given until CVP reaches 8 mm Hg (10 cm water) or PAOP reaches 12 to 15 mm Hg; however, patients on mechanical ventilation may require higher CVP levels. The quantity of fluid required often far exceeds the normal blood volume and may reach 10 L over 4 to 12 hours. PAOP or echocardiography can identify limitations in left ventricular function and incipient pulmonary edema due to fluid overload. Point-of-care ultrasound can also be used to assess volume status, including inferior vena cava (IVC) distention or collapsibility, cardiac function, and presence of pulmonary edema.

If a patient with septic shock remains hypotensive after CVP or PAOP has been raised to target levels, norepinephrine (highly individualized dosing) or vasopressin (up to 0.03 units/minute) may be given to increase mean blood pressure (BP) to at least 65 mm Hg. Epinephrine may be added if a second medication is needed. However, vasoconstriction caused by higher doses of these medications may cause organ hypoperfusion and acidosis.

Oxygen support


Parenteral antibiotics should be given as soon as possible after specimens of blood, body fluids, and wound sites have been taken for Gram stain and culture. Prompt empiric therapy, started immediately after suspecting sepsis, is essential and may be lifesaving. Antibiotic selection requires an educated guess based on the suspected source (eg, pneumonia, urinary tract infection), clinical setting, knowledge or suspicion of causative organisms and of sensitivity patterns common to that specific inpatient unit or institution, and previous culture results.

Typically, broad-spectrum gram-positive and gram-negative bacterial coverage is used initially; immunocompromised patients should also receive an empiric antifungal medication. There are many possible starting regimens; when available, institutional trends for infecting organisms and their antibiotic susceptibility patterns (antibiograms) should be used to select empiric treatment. In general, common antibiotics for empiric gram-positive coverage include vancomycin and linezolid. Empiric gram-negative coverage has more options and includes broad-spectrum penicillins (eg, piperacillin/tazobactam), 3rd- or 4th-generation cephalosporins, imipenems, and aminoglycosides. Initial broad-spectrum coverage is narrowed based on culture and sensitivity data.

Pearls & Pitfalls

  • Knowledge of institution- and care unit–specific trends in infecting organisms and their antimicrobial sensitivity is an important guide to empiric antibiotic selection.

Source control

The source of infection should be controlled as early as possible. IV and urinary catheters and endotracheal tubes should be removed if possible or changed. Abscesses must be drained, and necrotic and devitalized tissues (eg, gangrenous gallbladder, necrotizing soft-tissue infection) must be surgically excised. If excision is not possible (eg, because of comorbidities or hemodynamic instability), surgical drainage may help. If the source is not controlled, the patient’s condition will continue to deteriorate despite antibiotic therapy.

Other supportive measures

Normalization of blood glucose improves outcome in critically ill patients, even those not known to be diabetic, because hyperglycemia impairs the immune response to infection. A continuous IV insulin infusion (starting dose 1 to 4 units/hour) is titrated to maintain glucose between 110 and 180 mg/dL (7.7 to 9.9 mmol/L). This approach necessitates frequent (eg, every 1 to 4 hours) glucose measurement.

Corticosteroid therapy (eg, hydrocortisone < 400 mg IV per day in divided doses) is indicated for patients with adrenal insufficiency documented by cortisol testing. However, in refractory septic shock (systolic blood pressure < 90 mm Hg for more than 1 hour following both adequate fluid resuscitation and vasopressor administration, attainment of source control, and antibiotics), no cortisol testing is required before starting corticosteroid therapy (2 Treatment references Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more ). Continued treatment is based on patient response.

Treatment references

  • 1. Bhattacharjee P, Edelson DP, Churpek MM: Identifying patients with sepsis on the hospital wards. Chest 151:898–907, 2017. doi: 10.1016/j.chest.2016.06.02T

    2. Annane D, Pastores SM, Rochwerg B, et al: Guidelines for the diagnosis and management of critical illness-related corticosteroid insufficiency (CIRCI) in critically ill patients (Part I): Society of Critical Care Medicine (SCCM) and European Society of Intensive Care Medicine (ESICM) 2017. Intensive Care Med 43(12):1751-1763, 2017. doi: 10.1007/s00134-017-4919-5

Prognosis for Sepsis and Septic Shock

Overall mortality in patients with septic shock is decreasing and now averages 30 to 40% (range 10 to 90%, depending on patient characteristics). Poor outcomes often follow failure to institute early aggressive therapy (eg, within 6 hours of suspected diagnosis). Once severe lactic acidosis Lactic Acidosis Lactic acidosis is a high anion gap metabolic acidosis due to elevated blood lactate. Lactic acidosis results from overproduction of lactate, decreased metabolism of lactate, or both. (See also... read more with decompensated metabolic acidosis Metabolic Acidosis Metabolic acidosis is primary reduction in bicarbonate (HCO3), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly... read more becomes established, especially in conjunction with multiorgan failure, septic shock is likely to be irreversible and fatal. Mortality can be estimated with different scores, including the mortality in emergency department sepsis (MEDS) score. The multiple organ dysfunction score (MODS) measures dysfunction of 6 organ systems and correlates strongly with risk of mortality.

Key Points

  • Sepsis and septic shock are increasingly severe clinical syndromes of life-threatening organ dysfunction caused by a dysregulated response to infection.

  • An important component is critical reduction in tissue perfusion, which can lead to acute failure of multiple organs, including the lungs, kidneys, and liver.

  • Early recognition and treatment is the key to improved survival.

  • Resuscitate with intravenous fluids and sometimes vasopressors titrated to optimize central venous oxygen saturation (ScvO2) and preload, and to lower serum lactate levels.

  • Control the source of infection by removing catheters, tubes, and infected and/or necrotic tissue and by draining abscesses.

  • Give empiric broad-spectrum antibiotics directed at most likely organisms and switch quickly to more specific medications based on culture and sensitivity results.

Drugs Mentioned In This Article

Drug Name Select Trade
Aluvea , BP-50% Urea , BP-K50, Carmol, CEM-Urea, Cerovel, DermacinRx Urea, Epimide-50, Gord Urea, Gordons Urea, Hydro 35 , Hydro 40, Kerafoam, Kerafoam 42, Keralac, Keralac Nailstik, Keratol, Keratol Plus, Kerol, Kerol AD, Kerol ZX, Latrix, Mectalyte, Nutraplus, RE Urea 40, RE Urea 50 , Rea Lo, Remeven, RE-U40, RYNODERM , U40, U-Kera, Ultra Mide 25, Ultralytic-2, Umecta, Umecta Nail Film, URALISS, Uramaxin , Uramaxin GT, Urea, Ureacin-10, Ureacin-20, Urealac , Ureaphil, Uredeb, URE-K , Uremez-40, Ure-Na, Uresol, Utopic, Vanamide, Xurea, X-VIATE
Afrezza, Exubera
Albuked , Albumarc, Albuminar, Albuminex, AlbuRx , Albutein, Buminate, Flexbumin, Kedbumin, Macrotec, Plasbumin, Plasbumin-20
Pitressin, Vasostrict
Adrenaclick, Adrenalin, Auvi-Q, Epifrin, EpiPen, Epipen Jr , Primatene Mist, SYMJEPI, Twinject
FIRVANQ, Vancocin, Vancocin Powder, VANCOSOL
Zyvox, Zyvox Powder, Zyvox Solution
Zosyn, Zosyn Powder
A-Hydrocort, Ala-Cort, Ala-Scalp, Alkindi, Anucort-HC, Anumed-HC, Anusol HC, Aquaphor Children's Itch Relief, Aquaphor Itch Relief, Balneol for Her, Caldecort , Cetacort, Colocort , Cortaid, Cortaid Advanced, Cortaid Intensive Therapy, Cortaid Sensitive Skin, CortAlo, Cortef, Cortenema, Corticaine, Corticool, Cortifoam, Cortizone-10, Cortizone-10 Cooling Relief, Cortizone-10 External Itch Relief, Cortizone-10 Intensive Healing, Cortizone-10 Plus, Cortizone-10 Quick Shot, Cortizone-5 , Dermarest Dricort, Dermarest Eczema, Dermarest Itch Relief, Encort, First - Hydrocortisone, Gly-Cort , GRx HiCort, Hemmorex-HC, Hemorrhoidal-HC, Hemril , Hycort, Hydro Skin, Hydrocortisone in Absorbase, Hydrocortone, Hydroskin , Hydroxym, Hytone, Instacort, Lacticare HC, Locoid, Locoid Lipocream, MiCort-HC , Monistat Complete Care Instant Itch Relief Cream, Neosporin Eczema, NuCort , Nutracort, NuZon, Pandel, Penecort, Preparation H Hydrocortisone, Proctocort, Proctocream-HC, Procto-Kit, Procto-Med HC , Procto-Pak, Proctosert HC , Proctosol-HC, Proctozone-HC, Rectacort HC, Rectasol-HC, Rederm, Sarnol-HC, Scalacort, Scalpicin Anti-Itch, Solu-Cortef, Texacort, Tucks HC, Vagisil Anti-Itch, Walgreens Intensive Healing, Westcort
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
quiz link

Test your knowledge

Take a Quiz!