Monitoring tissue perfusion, oxygenation, and metabolism in critically ill patients.

Alterations in oxygen transport and use are integral to the development of multiple organ failure; therefore, the ultimate goal of resuscitation is to restore effective tissue oxygenation and cellular metabolism. Hemodynamic monitoring is the cornerstone of management to promptly identify and appropriately manage (impending) organ dysfunction. Prospective randomized trials have confirmed outcome benefit when preemptive or early treatment is directed toward maintaining or restoring adequate tissue perfusion. However, treatment end points remain controversial, in large part because of current difficulties in determining what constitutes "optimal." Information gained from global whole-body monitoring may not detect regional organ perfusion abnormalities until they are well advanced. Conversely, the ideal "canary" organ that is readily accessible for monitoring, yet offers an early and sensitive indicator of tissue "unwellness," remains to be firmly identified. This review describes techniques available for real-time monitoring of tissue perfusion and metabolism and highlights novel developments that may complement or even supersede current tools.