Renal oxygenation in clinical acute kidney injury

Renal oxygenation is defined as the relationship between renal oxygen delivery (DO 2 ) and renal oxygen consumption (VO 2 ) and it can easily be shown that the inverse of this relationship is equivalent to renal extraction of O 2 (O 2 Ex). An increase in renal O 2 Ex means that renal DO 2 has decreased in relation to renal VO 2 , i. e., renal oxygenation is impaired, and vice versa . When compared to other major organs, renal VO 2 is relatively high, second only to the heart. In sedated, mechanically ventilated patients, renal VO 2 is two-thirds (10 ml/min) that of myocardial oxygen consumption (15 ml/min) (Table 1 ) [ 1 , 2 ]. Renal blood flow, which accounts for approximately 20% of cardiac output, is three times higher than myocardial blood flow in this group of patients. Renal O 2 Ex in the non-failing kidney is therefore low, 10%, compared with, e.g., the heart, in which O 2 E X is 55% (Table 1 ).