Critical Care Medicine 978-1-4963-0291-5 chapter 27

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CHAPTER 27 • Sepsis and Septic Shock

Leukocytes

Inflammation

Endothelial cells

 Increased cytokine production  Adhesion molecule exposure

 Adhesion molecule ligand exposure  Chemokine receptors

Mediators

DIC initiation

 Chemotaxis  Release of TNF- a and IL-10  Phagocytic activity

 Tissue factor exposure  Activation of coagulation system  Thrombin generation

Platelets

Immune cells

Coagulation Immunosuppression

FIGURE 27-4.  Interactive inflammation, coagulation, and immunosuppressive sectors of the septic response.

a normal homeostatic response or conversely, be minimal or absent in the elderly, in patients with chronic renal failure, or in those receiving steroids or other anti-inflammatory drugs. Indeed, hypo- thermia occurs in approximately 10% of cases of overt sepsis and is a particularly poor prognostic sign, with mortality rates in hypothermic patients approaching 80%. This high mortality rate is not due to the reduced temperature itself but rather the close linkage of hypothermia with chronic underly- ing disease, shock, gram-negative bacteremia, and/ or a more ferocious host inflammatory response. Tachycardia, too, is an unreliable marker; it may be a sign of homeostatic behavior, rather than a sign associated with sepsis-defining organ dysfunction. Yet, unless patients have intrinsic cardiac conduc- tion system disease or are receiving medications to prevent tachycardia (e.g., β -blockers, calcium chan- nel blockers), tachycardia almost invariably accom- panies sepsis. Oliguria (urine output <0.5 mL/kg/h

for >2 hours), though a key clinical observation, may indicate an adaptive homeostatic response to hypovolemia, rather than organ injury by sepsis. Respiratory rate, on the other hand, is a key vital sign, because newly developed tachypnea is an early harbinger of advancing sepsis. Although it is pos- sible to have near-normal lung function with sep- sis, the diagnosis should be questioned in patients without tachypnea or abnormalities of gas exchange; more than 90% of patients develop hypoxemia suf- ficient to require supplemental oxygen (usually a PaO 2 /FiO 2 ratio below 300), and nearly 75% of life-threatening sepsis victims require noninvasive or invasive forms of mechanical ventilation. New abnormalities in circulating leukocyte (WBC) count (>10,000 cells/mm 3 or <4,000 cells/mm 3 ) occur fre- quently enough to be considered an important but highly nonspecific diagnostic criterion for sepsis. Among ICU patients, such leukocyte abnormalities are nearly universal.

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