Early and late acute respiratory distress syndrome: Two distinct clinical entities

Background: Despite numerous advances in surgical critical care and ventila tory management, mortality rates for acute respiratory distress syndrome (A RDS) have remained relatively constant. Pressure limited and non-pressure-l imited ventilatory techniques have been advocated with disparate results. W e hypothesized that there are two forms of ARDS, which may account for the conflicting clinical reports. Methods: Patients with posttraumatic ARDS were identified and reviewed, ARD S was defined as Pao(2)/Fio(2) ratio less than 200 with diffuse bilateral i nfiltrates on chest radiograph and no congestive heart failure. Patients we re analyzed relative to injury mechanism, transfusions, fluid balance, pres ence of pneumonia (defined as greater than or equal to 10(5) colony-forming units/mL in bronchoalveolar lavage effluent), and outcome. All were manage d with a non-pressure-limited strategy. Results: During a 5.5-year period, 178 patients with posttraumatic ARDS wer e identified. Mean Injury Severity Score and age were 29 and 40 years, resp ectively, Patients were stratified by time of ARDS diagnosis. Eighty-two pa tients (46%) had-early ARDS (within 48 hours after admission), and 96 patie nts (54%) had late ARDS (>48 hours between admission and diagnosis). There were no differences in Injury Severity Score, but the late group was signif icantly older. The early ARDS group was characterized by profound hemorrhag ic shock and had significant differences from the late group in incidence o f penetrating injury (30 vs, 10%; p < 0,001), admission base deficit (-7,7 vs. -4.2 mEq/L; p < 0,001), 48-hour transfusions (19.7 vs, 9.4; p < 0.0001) , initial 5-day fluid balance (19.9 vs. 10.1 L; p < 0,0001), and initial Pa o(2)/Fio(2) (121 vs. 141; p < 0,007). Pneumonia before ARDS was significant ly associated with late ARDS (38 vs. 9%; p < 0,001), ARDS-related mortality was primarily caused by hemorrhagic shock in the early group and progressi ve multiple organ failure in the late group. Conclusion: There are two distinct forms of posttraumatic ARDS, Early ARDS is characterized by hemorrhagic shock with capillary leak. Late ARDS freque ntly follows pneumonia and is associated with multiple system injury. Furth er studies should differentiate between these two distinct syndromes.