[Changes in tissue oxygen extraction in patients with acute respiratory insufficiency].

We analyzed the tissue oxygen extraction in 25 patients with acute respiratory failure. Fourteen met the clinical criteria for the adult respiratory distress syndrome (ARDS). The 11 remaining patients had acute respiratory failure with causes different from ARDS. In all cases the changes in the oxygen extraction ratio (O2ER) and in the oxygen consumption (VO2) were evaluated after changing oxygen availability (O2A) with positive end-expiratory pressure (PEEP) and dobutamine infusion. The patients with ARDS showed a change in VO2 parallel to O2A changes, with a significant correlation (r = 0.85); however, no changes were found in O2ER (r = 18). In the patients without ARDS, the changes in O2A did not modify the VO2 (r = 0.02) but there was a significant inverse relationship between DO2 and O2ER (r = -0.70). These findings suggest an abnormal regulation of tissue oxygen extraction and an abnormal dependence of VO2 on O2A in cases with ARDS. Dobutamine therapy, in addition to inotropic effects, could improve a situation of hidden hypoxia, as it is a vasodilator that might act on microvasculature.