Hemodynamic monitoring of critically ill patients, especially those who have ALI or ARDS, is a widely practiced compilation of techniques that largely have not been demonstrated to improve patient outcomes. Indeed, some techniques, such as use of the PAC, may actually be harmful. It seems unlikely that monitoring devices themselves are unreasonably risky to use. Rather it seems more likely that operator errors in gathering and interpreting hemodynamic data and in selecting the appropriate treatment strategies are the culprits. There is promise that ongoing clinical trials and better provider education will soon result in evidence-based recommendations for monitoring the circulation in this patient population.