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CHAPTER 19: SEVERE SEPSIS AND SEPTIC SHOCK

Robert S. Munford

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DEFINITIONS

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(Table 19-1) Animals mount both local and systemic responses to microbes that traverse their epithelial barriers and enter underlying tissues. Fever or hypothermia, leukocytosis or leukopenia, tachypnea, and tachycardia are cardinal signs of the systemic response. To date, attempts to devise precise definitions for the harmful systemic reaction to infection (“sepsis”) have not resulted in a clinically useful level of specificity, in part because the systemic responses to infection, trauma, and other major stresses can be so similar. In general, when an infectious etiology is proven or strongly suspected and the response results in hypofunction of uninfected organs, the term sepsis (or severe sepsis) should be used. Septic shock refers to sepsis accompanied by hypotension that cannot be corrected by the infusion of fluids.

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TABLE 19-1DEFINITIONS USED TO DESCRIBE THE CONDITION OF SEPTIC PATIENTS
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TABLE 19-1 DEFINITIONS USED TO DESCRIBE THE CONDITION OF SEPTIC PATIENTS
Bacteremia Presence of bacteria in blood, as evidenced by positive blood cultures
Signs of possibly harmful systemic response Two or more of the following conditions: (1) fever (oral temperature >38°C [>100.4°F]) or hypothermia (<36°C [<96.8°F]); (2) tachypnea (>24 breaths/min); (3) tachycardia (heart rate >90 beats/min); (4) leukocytosis (>12,000/μL), leukopenia (<4000/μL), or >10% bands
Sepsis (or severe sepsis) The harmful host response to infection; systemic response to proven or suspected infection plus some degree of organ hypofunction, i.e.:
1. Cardiovascular: Arterial systolic blood pressure ≤90 mmHg or mean arterial pressure ≤70 mmHg that responds to administration of IV fluid
2. Renal: Urine output <0.5 mL/kg per hour for 1 h despite adequate fluid resuscitation
3. Respiratory: Pao2/Fio2 ≤250 or, if the lung is the only dysfunctional organ, ≤200
4. Hematologic: Platelet count <80,000/μL or 50% decrease in platelet count from highest value recorded over previous 3 days
5. Unexplained metabolic acidosis: A pH ≤7.30 or a base deficit ≥5.0 mEq/L and a plasma lactate level >1.5 times upper limit of normal for reporting lab
Septic shock Sepsis with hypotension (arterial blood pressure <90 mmHg systolic, or 40 mmHg less than patient’s normal blood pressure) for at least 1 h despite adequate fluid resuscitationa
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Need for vasopressors to maintain systolic blood pressure ≥90 mmHg or mean arterial pressure ≥70 mmHg
Refractory septic shock Septic shock that lasts for >1 h and does not respond to fluid or pressor administration

aFluid resuscitation is considered adequate when the pulmonary artery wedge pressure is ≥12 mmHg or the central venous pressure is ≥8 mmHg.

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ETIOLOGY

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Image not available. The systemic response to any class of microorganism can be harmful. Microbial invasion of the bloodstream is not essential because local inflammation can also elicit distant organ dysfunction and hypotension. In fact, blood cultures yield bacteria or fungi in only ~20–40% of cases of severe sepsis and 40–70% of cases of septic shock. In a prevalence study of 14,414 patients in intensive care units (ICUs) from 75 countries in 2007, 51% of patients were considered infected. Respiratory infection was most common (64%). Microbiologic results were positive in 70% of individuals considered infected; of the isolates, 62% were gram-negative bacteria (Pseudomonas species and Escherichia coli were most ...

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