Đang tải... (xem toàn văn)
(BQ) Part 2 book Harrison''s pulmonary and critical care medicine presents the following contents: Common critical illnesses and syndromes, disorders complicating critical illnesses and their management, laboratory values of clinical importance.
Section IV Common Critical Illnesses and Syndromes CHAPTER 28 SEVERE SEPSIS AND SEPTIC SHOCK robert s munford DefinitionS epiDeMiology (See Table 28-1) 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 the cardinal signs of the systemic response, that is often called the systemic inflammatory response syndrome (SIRS) SIRS may have an infectious or a noninfectious etiology If infection is suspected or proven, a patient with SIRS is said to have sepsis When sepsis is associated with dysfunction of organs distant from the site of infection, the patient has severe sepsis Severe sepsis may be accompanied by hypotension or evidence of hypoperfusion When hypotension cannot be corrected by infusing fluids, the diagnosis is septic shock These definitions were developed by consensus conference committees in 1992 and 2001 and have been widely used; there is evidence that the different stages may form a continuum Severe sepsis is a contributing factor in >200,000 deaths per year in the United States The incidence of severe sepsis and septic shock has increased over the past 30 years, and the annual number of cases is now >700,000 (∼3 per 1000 population) Approximately two-thirds of the cases occur in patients with significant underlying illness Sepsis-related incidence and mortality rates increase with age and preexisting comorbidity The rising incidence of severe sepsis in the United States is attributable to the aging of the population, the increasing longevity of patients with chronic diseases, and the relatively high frequency with which sepsis develops in patients with AIDS The widespread use of immunosuppressive drugs, indwelling catheters, and mechanical devices also plays a role Invasive bacterial infections are prominent causes of death around the world, particularly among young children In sub-Saharan Africa, for example, careful screening for positive blood cultures found that community-acquired bacteremia accounted for at least one-fourth of deaths of children >1 year of age Nontyphoidal Salmonella species, Streptococcus pneumoniae, Haemophilus influenzae, and Escherichia coli were the most commonly isolated bacteria Bacteremic children often had HIV infection or were severely malnourished etiology Sepsis can be a response to any class of microorganism Microbial invasion of the bloodstream is not essential, since 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 Individual gram-negative or gram-positive bacteria account for ∼70% of these isolates; the remainder are fungi or a mixture of microorganisms (Table 28-2) In patients whose blood cultures are negative, the etiologic agent is often established by culture or microscopic examination of infected material from a local site; specific identification of microbial DNA or RNA in blood or tissue samples is also used In some case series, a majority of patients with a clinical picture of severe sepsis or septic shock have had negative microbiologic data pathophySiology Most cases of severe sepsis are triggered by bacteria or fungi that not ordinarily cause systemic disease in immunocompetent hosts (Table 28-2) To survive within the human body, these microbes often exploit deficiencies in host defenses, indwelling catheters or other foreign matter, or obstructed fluid drainage conduits Microbial pathogens, in contrast, can circumvent innate defenses because they (1) lack molecules that can be recognized by host receptors (see later) or (2) elaborate toxins or other virulence factors In both 276 Table 28-1 277 Definitions Used to Describe the Condition of Septic Patients Bacteremia Septicemia Systemic inflammatory response syndrome (SIRS) Sepsis Severe sepsis (similar to “sepsis syndrome”) Septic shock Critical illness–related corticosteroid insufficiency (CIRCI) A grading system that stratifies patients according to four key aspects of illness; attempts to define subgroups of patients, reducing heterogeneity in clinical trials Inadequate corticosteroid activity for the patient’s severity of illness; should be suspected when hypotension is not relieved by fluid administration Source: Adapted from the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference Committee Table 28-2 Microorganisms Involved in Episodes of Severe Sepsis at Eight Academic Medical Centers Episodes with Bloodstream Infection, % (n = 436) Episodes with Documented Infection but No Bloodstream Infection, % (n = 430) Total Episodes, % (n = 866) Gram-negative bacteria 35 44 40 b 40 24 31 Microorganism a Gram-positive bacteria a Fungi 7 5 6 Polymicrobial 11 21 16 Classic pathogensc 12,000/μL), leucopenia (10% bands; may have a noninfectious etiology SIRS that has a proven or suspected microbial etiology Sepsis with one or more signs of organ dysfunction—for example: 1. Cardiovascular: Arterial systolic blood pressure ≤90 mmHg or mean arterial pressure ≤70 mmHg that responds to administration of intravenous fluid 2. Renal: Urine output