Evidence-based approaches to assessing the clinical literature are used increasingly in issues relating to critical care medicine. As we discussed previously, this approach attempts to provide a logical and convenient framework from which the quality and relevance of clinical studies may be assessed in an unbiased manner. An evidence-based approach also allows the reader to differentiate between solid evidence and evidence that is based on a presumed mechanism, standard practice, or conventional wisdom. Evidence-based medicine that deemphasizes intuition, unsystemic clinical experience, and pathophysiologic rationale is sufficient grounds for clinical decision making and stresses the examination of evidence from clinical research. Importantly, it is the objective nature by which the evidence-based medicine paradigm approaches the questions of "What are we doing" and "How can we do better," that causes health care providers and funding agencies to increasingly adopt this paradigm as a primary principle. The role of evidence-based medicine, therefore, is not to discount expert opinion but, wherever possible, to require that recommendations be based on the results of rigorous and controlled scientific study. We introduced this article by highlighting the growing imbalance between resources and patient needs in the critical care environment. At the level of diagnostic technology and therapeutic care plans, critical care professionals increasingly are asked to identify strategies to improve efficiencies-approaches with rigorous costs that at the same time promote better patient care. Formalized technology assessment is one of the mechanisms to accomplish this. Using critical appraisal within the context of evidence-based medicine is one of the mechanisms by which data can be synthesized to describe technology assessment. In this example, we used controversies surrounding use of pulmonary artery catheterization in critically ill patients to highlight some of the principles of evidence-based medicine at the bedside. We introduced how a particular case example can be used to ask the question, "What is the evidence that a particular diagnostic technology or therapeutic modality improves outcome?" In the case of PACs, no one would argue that a diagnostic technology a priori leads to improved outcome; rather, we have to presume that given good data, the care provider will apply the most appropriate management strategy. In this case example, however, we demonstrate how the critical appraisal process should identify a search strategy to find the most appropriate evidence to support the questioning process. From this, the evidence can be critically appraised and tabulated. In the case of the PAC, Table 13 demonstrates that there are few data to identify a grade A recommendation that the PAC should be used as part of the care process in critically ill patients. Finding that there is little evidence to support the use of pulmonary artery catheterization in the clinical literature does not mean that this diagnostic technology is neither efficacious nor effective. It might well be that information provided by PACs is important in the care process. However, what this exercise has taught us is that there is little objective evidence to support this conclusion. The challenge to critical care practitioners is not only to apply the evidence-based processes more frequently to our environment but also to use the information to separate out clearly what is fact versus opinion. Where there is little evidence to support a particular clinical practice, as we have demonstrated with the PAC review earlier, the challenge to the clinician should be the design and conduct of clinical trials clarifying debate between opinion and evidence.