Thirty multiply injured blunt-trauma patients at high risk for development of ARDS (multisystem trauma including more than one organ or extremity, Injury Severity Score of 26 or more, hypotension and need for 1500 mL or more blood within the first hour after admission, and PaO2 ≤ 70 torr) were studied sequentially with blood and physiologic evaluations beginning immediately after injury and every eight hours for eight days, or until death, to study the evolution of the ARDS process. Mixed venous blood samples were obtained for eicosanoids PGE2, PGF(2α), thromboxane B2, PGI2 (6-KetoPGF(1α)) and leukotriene B4 (LTB4). Platelet (PLAT), and neutrophil (WBC) counts were also done and plasma elastase was measured. At 7:00 AM each day patient neutrophils were obtained for a study of zymosan-activated superoxide production using a chemiluminescence assay. These data were correlated with physiologic measurements of the Respiratory Index (RI), per cent pulmonary shunt (QS/QT), and respiratory compliance measures. Seven patients developed a fulminant post-traumatic ARDS syndrome within 96 hours after injury. Twelve patients without ARDS developed sepsis (TS) four or more days after injury, and 11 had uncomplicated postinjury courses (TR). Compared to both TR and TS, ARDS had a significant (p < 0.01) rise in neutrophil superoxide production beginning on day 2 through day 4 after injury. This was preceded by rises in PGE2 and LTB4, which were significantly correlated with subsequent falls in PLAT and WBC and rises in TXB2, PGF1, and superoxide production and followed by increases in RI, QS/QT, and a fall in compliance. The significant difference in the pattern and sequence of events in ARDS compared to TR and TS patients suggests that in ARDS the earliest event may be related to peripheral release of PGE2 and LTB4 due to platelet activation and lung sequestration with release of PGF(2α), and by aggregation and leukocyte adherence with release of elastase. However, fulminant ARDS mortality appears to be related to the subsequent amplification of the LTB4 leukocyte activation with superoxide production that does not achieve significance before the second day after injury and rises to a maximum by day 4 after injury. These data suggest that post-trauma ARDS follows a different evolutionary pattern than that reported in animal models and is also different from that seen in human TS or TR patients. They also suggest that a therapeutic window may exist between platelet and white cell endothelial adherence-aggregation (sequestration) with proteolytic degranulation (elastase release) and the subsequent WBC activation producing toxic superoxides and lung gas exchange abnormalities.
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