Acute respiratory distress syndrome...

Acute respiratory distress syndrome (ARDS) directs to the syndrome of lung injury characterized by means of dyspnea, severe hypoxemia, decreased lung compliance, and diffuse bilateral pulmonary infiltrates. Family physicians can play an essential part in the early recognition of ARDS and contribute to the multispecialty team required to manage this life-threatening condition. This article reviews the present understanding of the pathophysiology, management, and prognosis of ARDS.

Originally referr to as traumatic wet lung clash lung, or congestive atelectasis, ARDS was recognized in 1967 when the clinical, physiologic, radiographic, and pathologic abnormalities that were unique to a assign places to of 12 patients were described, distinguishing them from other cases in a series of 272 patients treated for respiratory failure. (1) A National Institutes of Health (NIH) panel initially estimated an incidence of 75 by 100,000 persons per year, nevertheless subsequent prospective studies give a range of 126 to 18 by 100,000 persons annually. (2,3) strife of words still exists about the correct incidence because of differing criteria used to define ARDS. The prevalence of ARDS is reported to be between 15 and 18 percent of all ventilated patients. (4) While a mortality rate greater than 50 percent is reported in the majority of clinical investigations performed between 1979 and 1994 more novel studies show a decline in mortality to be between 32 and 45 percent (256)

Definitions of ARDS

Before 1992 the acronym ARDS take the part ofed the adult respiratory distress syndrome The American-European Consensus Committee in succession ARDS standardized the definition (7) in 1994 and renamed it acute rather than adult respiratory distress syndrome because it happens at all ages. The limit acute lung injury (ALI) was also introduced at that time. The committee commended that ALI be defined as "a syndrome of inflammation and increased permeability that is associated with a constellation of clinical, radiologic, and physiologic abnormalities that cannot be explained according to but may coexist with, left atrial or pulmonary capillary hypertension." (7) Exclusion of left atrial hypertension as the primary cause of hypoxemia is critical to this definition, and measurement of pulmonary capillary wedge crushing may be necessary. The distinction between ALI and ARDS is the order of hypoxemia, (7) defined on the ratio of arterial oxygen tension to fractional inspired oxygen concentration (Pa[O.sub.2]/Fi[O.sub.2]), as shown in Table 1 (8) ALI is defined by way of a ratio less than 300 mm Hg and 200 mm Hg or les is required for ARDS.

Risk Factors

Multiple risk factors for the progress to maturity of ARDS have been identified (Table 2) (9) The sepsis syndrome appears to be the mostly common, but the overall risk increases with multiple factors. (10) line transfusion is an independent risk factor. (11) Advanced age and cigarette smoking are associated with an increased risk of developing ARDS, while alcohol consumption appears to have no influence. (12) A review of the 1993 National Mortality succeed Back Study Database determined that the annual ARDS mortality is slowly declining, moreover that men and blacks have a higher mortality rate compared with women and other racial collections (13)

Pathophysiology

In ARDS, the injured lung is believed to go on through three phases: exudative, proliferative, and fibrotic, however the course of each phase and the overall disease progression is variable. In the exudative phase, damage to the alveolar epithelium and vascular endothelium bring into views leakage of water, protein, and inflammatory and r progeny cells into the interstitium and alveolar lumen These changes are induced by dint of a complex interplay of proinflammatory and anti-inflammatory mediators.

image I alveolar cells are irreversibly damaged and the denud space is replaced through the deposition of proteins, fibrin, and cellular debris, producing hyaline membranes, while injury to the surfactant-producing impressed sign II cells contributes to alveolar collapse. In the proliferative phase, pattern II cells proliferate with a certain epithelial cell regeneration, fibroblastic reaction, and remodeling. In near patients, this progresses to an irreversible fibrotic phase involving collagen deposition in alveolar, vascular, and interstitial beds with exhibition of microcysts. (14)

Clinical Presentation

About 50 percent of patients who lay open ARDS do so within 24 hours of the inciting result At 72 hours, 85 percent of patients have clinically apparent ARDS. (3) Patients initially have tachypnea, dyspnea, and normal auscultatory findings in the chest. an elderly patients may present with an unexplained altered mental status. Patients then become tachycardic with mild cyanosis and later disentangle coarse rales. They progress to respiratory distress with diffuse rhonchi and signs of consolidation, many times requiring positive pressure ventilatory support. flat with significant hypoxemia, these clinical findings may not be obvious, in the way that an arterial blood gas is warranted early in patients at risk. Initial oxygenation ratios and ventilatory parameters do not reliably predict the ultimate consequence in individual patients.