Mechanical Ventilation and Lung–Kidney Interactions

t was not so long ago that the term "pulmonary-renal syndrome" was synonymous with the combination of im- mune alveolar hemorrhage and rapidly progressive glo- merulonephritis caused by rare conditions such as Goodpas- ture's disease and Wegener's granulomatosis. Recent elucidation of the pathobiology of critical illness has led to a more basic mechanistic understanding of the complex interplay between injured organs in patients with multiple organ dys- function syndrome; this has been aptly called the "slippery slope of critical illness" (1). Distant organ effects of apparently isolated injuries to the lungs, gut, and kidneys have all been discovered in recent years. In this article, we review the harm- ful bidirectional interaction between acute lung injury (ALI) and acute kidney injury (AKI), which appears to be a common clinical syndrome with routine clinical implications, rather than a rare autoimmune catastrophe. We will review the current understanding of lung-kidney interactions from both perspec- tives, including the renal effects of ALI and mechanical venti- lation, the pulmonary sequelae of AKI, and the emerging evi- dence of deleterious bidirectional organ cross-talk between lung and kidney.