EXPLORING the ROLE of CENTRAL VENOUS OXYGEN SATURATION in the EVALUATION and MANAGEMENT of SEVERE HYPOXEMIA in MECHANICALLY VENTILATED PATIENTS

Background: Although central venous oxygen saturation (ScvO2) has been used as an endpoint for the treatment of circulatory shock, its role in guiding the evaluation and treatment of patients with severe hypoxemia remains to be assessed. The aim of this study was to assess the incidence of low ScvO2 in a cohort of hypoxemic patients and the association of this finding with differences in clinical management and patient outcomes. Methods: Retrospective review of data from adult intensive care unit patients with hypoxemia who required invasive mechanical ventilation for over 24 h and had at least one ScvO2 measured within 6 h of a PaO2/FiO2 ratio <200. Results: Of 442 mechanically ventilated patients with severe hypoxemia, 249 (56%) had an ScvO2 <70%. When compared with patients with ScvO2 ≥70%, those with low ScvO2 had worse systemic oxygenation and hemodynamic parameters and were more likely to receive red blood cell transfusions (31.7% vs. 18.1%, P = 0.001), epinephrine (27.3% vs. 16.6%, P = 0.007), and inodilators. Outcomes such as median intensive care unit length of stay (7.5 vs. 8.3 days, P = 0.337) and hospital mortality (39.8% vs. 35.7%, P = 0.389) were not different between groups. When stratified by the central venous-to-arterial CO2 difference (ΔPCO2), patients with a low ScvO2 and normal ΔPCO2 had lower median PaO2 and hemoglobin levels and received more red blood cell transfusions, whereas those with an increased ΔPCO2 had a lower pulse pressure and cardiac index and were more likely to receive epinephrine and milrinone. Conclusion: Low ScvO2 is frequently observed in mechanically ventilated patients with severe hypoxemia, and these patients receive different interventions. Clinicians often use therapies targeting systemic oxygen delivery to correct low ScvO2. Prospective research is needed to identify patients with severe hypoxemia that might benefit from interventions targeting systemic oxygen delivery.