Oxygen transport and utilization.

The evaluation and management of oxygen delivery (Do2) and consumption (Vo2) of patients with acute medical and surgical illnesses have been subject to controversy and reevaluation. It has been established that a relationship between oxygen delivery and oxygen consumption exists, and is very complex, particularly in diseases in which various factors individually or collectively affect it. The care of critically ill patients routinely involves the manipulation of the Vo2-Do2 relationship, and extensive research, both experimental and clinical, has been done to improve our understanding of this relationship in health and disease with the hope for improved outcomes. Regional measures of oxygenation are a relatively new area of interest with a limited amount known about the regional relationship between Do2 and Vo2. The adequacy of regional oxygenation appears to play an important role in organ dysfunction in critical illness. Standard measures of assessing systemic oxygenation are often insensitive in detecting tissue hypoxia, which can often vary among and within various organs. New noninvasive technologies to measure the adequacy of regional measures of oxygenation are being developed, with gastrointestinal tonometry getting much clinical attention. The exact role of these technologies in the management of critically ill patients, and whether they will improve survival, has not yet been determined. It is likely that the ability to care successfully for critically ill patients will come from a better understanding of not only global, but also regional, cellular, and subcellular metabolism.