[Pathophysiology and strategy of shock in terms of tissue oxygen metabolism]

In both septic shock and hypovolemic shock, global oxygen consumption is characterized by the supply dependency phenomenon, which suggests tissue hypoxia. The conventional measurements of blood lactate level, oxygen delivery/oxygen consumption, and mixed venous oxygen saturation may not provide reliable information on the adequacy of tissue oxygenation. The intestinal mucosal villus is particularly vulnerable to a reduction in oxygen delivery because of the countercurrent mechanism. Intestinal mucosal hypoxia may have important clinical ramifications as it has been implicated in the etiology of bacterial translocation and cytokine synthesis. Gastric tonometry has been proposed as a simple, relatively noninvasive technique to detect occult tissue hypoxia. Since gastric intramucosal PCO2 is directly related to arterial PCO2, the gradient between gastric and arterial PCO2 is recommended as a sensitive and specific index of intestinal hypoperfusion. Although the effects of therapeutic interventions are far from consistent, dobutamine, but not dopamine, appears to increase intestinal mucosal blood flow in critically ill patients the most consistently. Further studies are needed to demonstrate the effects of other agents, such as angiotensin-converting enzyme inhibitor and vasodilator prostaglandins. Plasma volume expansion with colloid solution may improve the splanchnic microvascular blood flow. Older stored-blood transfusion, however, may lead to tissue hypoxia.