Differential cardiovascular responses during weaning failure: effects on tissue oxygenation and lactate

Objective To test the following two hypotheses during weaning failure: (a) mixed venous oxygen saturation (SvO₂) does not decrease in patients whose oxygen consumption does not increase, and (b) blood lactate may increase in patients who demonstrate substantial decreases in SvO₂.Design and setting A prospective observational and physiological study in a 30-bed university intensive care unit.Patients and participants 18 patients who failed weaning and 12 patients who succeeded weaning (controls).Measurements and results Hemodynamics, global tissue oxygenation, cardiovascular response (cardiac index/oxygen extraction diagram), and blood lactate were measured in ventilator-supported patients undergoing a spontaneous breathing trial. In patients who failed without having increased their oxygen consumption (n=9) the increase in oxygen delivery was accompanied by a decrease in oxygen extraction (by 15±4%). In patients who failed (n=9) having increased their oxygen consumption (by >10%) this increase was met mainly by an increase in oxygen extraction (by 30±7%). SvO₂ increased by 2±1% in the former patients, whereas it decreased by 20±5% in the latter. Arterial lactate increased (range 2.3–3.1 mM/l) in only three patients who failed to have increased oxygen consumption and exhibited heart failure and the highest decreases in SvO₂ (by 12–39%).Conclusions Patients whose SvO₂ does not decrease during weaning failure do not have increased oxygen consumption probably due to respiratory center depression in some of them. Patients whose SvO₂ decreases have increased oxygen consumption.Electronic Supplementary Material Electronic supplementary material to this paper can be obtained by using the Springer Link server located at .This article refers to the editorial available at