Adequate tissue oxygenation is one of the main therapeutic goals for the critically ill patient. Until recently, the perfusion status of the critically ill and injured has been assessed by global indices such as blood pressure, heart rate, and urine output. However, these global parameters are inadequate in that they fail to demonstrate the actual perfusion status of a patient. Research has shown the splanchnic region to be a pivotal organ bed in response to shock. Because this region shows early signs of hypoperfusion and hypoxia, its monitoring provides for more effective and complete resuscitation. To that end, gastric tonometry offers a noninvasive means by which early symptoms of low flow can be determined, allowing for optimization of tissue perfusion and patient outcome. The most proximal segment of the gastrointestinal tract offers promising information regarding tissue perfusion with the use of sublingual capnography.