Oxygen delivery in critical illness.

Oxygen consumption is physiologically dependent on DO2 below the critical DO2. Thus, patients in overt shock have physiologic dependence of VO2 on DO2. The first priority of prevention and reversal of tissue hypoxia is to balance oxygen demand and oxygen supply. Pathologic dependence of VO2 on DO2 has not yet been demonstrated convincingly in critically ill patients. Furthermore, in our opinion, contradicting results of RCTs of supernormal DO2 versus normal DO2 do not support routine maintenance of supernormal levels of DO2. Finally, we suggest that intensivists continue to assess DO2 and VO2 carefully. Global assessment of VO2 and DO2 appears inadequate to detect occult tissue hypoxia in most critically ill patients. However, research focused on regional assessment such as gastric tonometer measurement of gastric mucosal PCO2 and pH provides opportunity for safe, convenient detection of occult tissue hypoxia in critically ill patients.