Evaluating hypoxemia in the critically ill

Prompt correction of hypoxemia is a basic goal in the treatment of critically ill patients. Improvements in global oxygen delivery may be achieved by several means, such as providing an adequate fraction of inspired oxygen and using packed red blood cell transfusions for volume resuscitation. Low levels of positive end-expiratory pressure often help improve arterial oxygen tension. Measurement of mixed venous oxygen saturation (Sv̄O₂) can be useful in patient assessment. Sv̄O₂ may be decreased in patients with hypoxemia, hypovolemia, or anemia and may be elevated in patients with sepsis. Serum lactate levels may not quantitate the degree of tissue hypoxia, but serial measurements can help monitor the patient's response to therapy. For patients with septic or hypovolemic shock, early fluid resuscitation with isotonic crystalloid solution is essential. Catecholamine vasopressors can be useful when fluid administration fails to restore adequate blood pressure.