CLINICAL-ASSESSMENT OF TISSUE OXYGENATION

As technology related to ventilatory and hemodynamic support has evolv ed, so too have our means of assessing the patient's response to these interventions. Moreover, while technological advances in monitoring h ave improved our understanding of the cardiopulmonary systems, they ha ve also complicated the care of the critically ill. At this time, a gr eat deal of controversy surrounds the interpretation of clinical data relevant to the adequacy of tissue oxygenation. For instance, in the d iseased state, there is ample evidence suggesting that inadequate tiss ue oxygenation commonly occurs in the absence of overt circulatory sho ck. Indices such as blood pressure (BP), cardiac output (CO), lactate and mixed venous oxygen saturation (SvO2), previously relied upon to r eflect adequate oxygen delivery (DO2), are now recognized to be inadeq uate indices of DO2, since they are often normal despite the presence of significant tissue hypoxia.(1-5) Although these concepts are now fa miliar to most intensivists, there remains a lack of consensus regardi ng which tests are the most sensitive indicators of tissue hypoxia in critically ill patients. This review will focus on the clinical applic ations and limitations of noninvasive and invasive techniques, which h ave been employed to assess tissue oxygenation in the critically ill ( Table 1).