Epidemiology and etiology

Sepsis is the leading cause of morbidity and mortality for critically ill patients, and the tenth leading cause of death overall.1, Sepsis causes 660,000 to 750,000 cases annually, a fourfold increase from 1979.1,4,5 Care of septic patients costs $17 billion in the United States annually ($22,000-$50,000 per patient).4,6

Table 82-1 Definitions Related to Sepsis

Bacteremia (fungemia): Presence of viable bacteria or fungi in the bloodstream Infection: Inflammatory response to invasion of normally sterile host tissue by microorganisms SIRS: A systemic inflammatory response to a variety of clinical insults which can be infectious, but can have a noninfectious etiology. The response is manifested by two or more of the following conditions: temperature greater than 38°C (100.4°F) or less than 36°C (96.8°); pulse greater than 90 bpm;

respiratory rate greater than 20 breaths/min or PaCO2 less than 32 torr; WBC count greater than 12 x 103/mm3 (12 x 109/L), less than 4 x 103/mm3 (4 x 109/L), or greater than 10% immature (band) forms

Sepsis: The SIRS and documented infection (culture or Gram stain of blood, sputum, urine, or normally sterile body fluid positive for pathogenic microorganisms Severe sepsis: Sepsis associated with organ dysfunction, hypoperfusion, or hypotension (systolic blood pressure less than 90 mm Hg). Hypoperfusion and perfusion abnormalities may include, but are not limited to, lactic acidosis, oliguria, or acute alteration in mental status Septic shock: Sepsis with hypotension, despite fluid resuscitation, along with the presence of perfusion abnormalities. Patients who are on inotropic or vasopressor agents may not be hypotensive at the time perfusion abnormalities are measured MODS: Presence of altered organ function requiring intervention to maintain homeostasis

MODS, multiple-organ dysfunction syndrome; PaCO2, partial pressure of carbon dioxide; SIRS, systemic inflammatory response syndrome.

Risk factors for sepsis include: age, cancer, immunodeficiency, chronic organ failure, genetic factors (male, and nonwhite ethnic origin in North America), bacteremic patients, and polymorphisms in genes that regulate immunity.4,7-10 Pulmonary, GI,

genitourinary, and bloodstream infections account for the majority of sepsis cases. ' '

'0' Gram-positive and gram-negative bacteria, fungal species, and viruses cause sepsis (Table 82-2). Gram-positive infections account for 30% to 50% of sepsis and

septic shock cases. The percentages of gram-negative, polymicrobial, and viral sepsis cases are 25%, 25%, and 4%, respectively.4,7, ,11 Multidrug resistant (MDR)

bacteria are responsible for approximately 25% of sepsis cases, are difficult to treat,

and increase mortality. ' The rate of fungal infections increased 200% from 1979 to 2000.4 Candida albicans is the most common fungal species; however, nonalbic-ans species (C. glabrata, C. krusei, and C. tropicalis) have increased from 24% to 46% 4,ll,l2 Other fungi identified as causes of sepsis include Cryptococcus, Cocci-dioides, Fusarium, and Aspergillus.

Table 82-2 Pathogens in Sepsis

Organism

Frequency (%)

Gram-positive bacteria

30-50

Methicillin-susceptible Staphylococcus aureus

14-24

Met hldllin-resistant Staphylococcus act feus

5-11

Other staphylococcus speries

1-3

Streptococcus pneumoniae

9-12

Other Streptococcus species

6-11

Enterocdcojs species

3-13

Anaerobes

1-2

Other gram-positive bacteria

1-5

Gram-negative bacteria

25-30

Escherichia coli

9-27

Pseudomonas aeruginosa

8-15

Klebsiella pneumoniae

2-7

Enterobacter species

6-16

Haemophilus influenzae

2-10

Anaerobes

3-7

Other gram-negative bacteria

3-12

Fungi

Candida albicans

1-3

Other Candida species

1-2

Parasites

1-3

Viruses

PATHOPHYSIOLOGY

The development of sepsis is complex and multifactorial. The normal host response to infection is designed to localize and control bacterial invasion and initiate repair of injured tissue through phagocytic cells and inflammatory mediators.1 Sepsis results when the inflammatory response becomes exaggerated and extends to normal tissue distant from the initial tissue site.

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