Serial changes in surfactant-associated proteins in lung and serum before and after onset of ARDS

The goal of this study was to determine the changes that occur in surfactan t-associated proteins in bronchoalveolar ravage fluid (BAL) and serum of pa tients at risk for ARDS and during the course of ARDS. We found that the co ncentrations of SP-A and SP-B were low in the BAL of patients at risk for A RDS before the onset of clinically defined lung injury, whereas the concent ration of SP-D was normal. In patients with established ARDS, BAL SP-A and SP-B concentrations were low during the entire 14-d observation period, but the median SP-D concentrations remained in the normal range. Immunoreactiv e SP-A and SP-D were not increased in the serum of patients at risk for ARD S, but both increased after the onset of ARDS to a maximum on Day 3 and rem ained elevated for as long as 14 d. The BAL SP-A concentrations were signif icantly lower in at-risk patients who developed ARDS, and no patient with a BAL SP-A concentration greater than 1.2 mu g/ml developed ARDS. On Days 1 and 3 of ARDS, the BAL SP-D concentration was significantly lower in patien ts who died, and the BAL SP-D concentration was significantly related to th e Pl(O2)/Fl(O2), ratio. Thus, surfactant protein abnormalities occur before and after the onset of ARDS, and the responses of SP-A, SP-B, and SP-D dif fer in important ways. The BAL SP-A and SP-D measurements can be used to cl assify patients as high or low risk for progression to ARDS and/or death af ter the onset of ARDS. Strategies to increase these surfactant proteins in the lungs of patients with ARDS could be useful to modify the onset or the course of ARDS.