Ventriculo-arterial uncoupling is associated with VO 2 dependency in cardiac surgical patients

Background The clinical relevance of V-A (un)coupling in critically ill patients is under investigation. In this study we measured the association between V-A coupling and oxygen consumption (VO 2 ) response in patients with acute circulatory instability following cardiac surgery. Methods and results Sixty-one cardio-thoracic ICU patients who received fluid challenge or norepinephrine infusion were included. Arterial pressure, cardiac output (CO), heart rate (HR), arterial (E A ), and ventricular elastances (E V ), total indexed peripheral resistance (TPRi) were assessed before and after hemodynamic interventions. VO 2 responders were defined as VO 2 increase > 15 %. V-A coupling was evaluated by the ratio E A /E V. Left ventricle stroke work (SW) to pressure volume area (PVA) ratio was calculated. In the overall population, 24 patients (39%) were VO 2 responders and 48 patients were uncoupled (i.e., E A /E V ratio > 1.3): 1.9 (1.6-2.4). Most of the uncoupled patients were classified as VO 2 responders (28 of 31 patients, p=0.031). Changes in VO 2 were correlated with those of TPRi, E A , E A /E V and CO. E A /E V ratio predicted VO 2 increase with an AUC of 0.76 [95 % CI: 0.62-0.87]; p=0.001. In multivariate and principal component analyses, E A /E V and SW/PVA ratios were independently associated (P < 0.05) with VO 2 response following interventions. Conclusions VO 2 responders were characterized by baseline V-A uncoupling due to high E A and low E V . Baseline E A /E V and SW/PVA ratios were associated with VO 2 changes independently of the hemodynamic intervention used. These results further underline the pathophysiological significance of V-A uncoupling in patients with hemodynamic instability.