ARDS/ALI is most often seen as part of a systemic inflammatory response syndrome (SIRS), particularly systemic sepsis. The lung findings parallel the damage in other tissues, namely, widespread destruction of the capillary endothelium, extravasation of protein rich fluid and interstitial edema. The alveolar basement membrane becomes damaged and fluid leaks into the airspaces, reducing lung compliance and causing ventilation-perfusion mismatch.