Association of low mixed venous oxygen saturations during early ICU stay with increased 30-day and 1-year mortality after cardiac surgery: a single-center retrospective study

Abstract

Abstract Background Low postoperative mixed venous oxygen saturation (SvO2) values have been linked to poor outcomes after cardiac surgery. The present study was designed to assess whether SvO2 values of < 60% at intensive care unit (ICU) admission and 4 h after admission are associated with increased mortality after cardiac surgery. Methods During the years 2007–2020, 7046 patients (74.4% male; median age, 68 years [interquartile range, 60–74]) underwent cardiac surgery at an academic medical center in Finland. All patients were monitored with a pulmonary artery catheter. SvO2 values were obtained at ICU admission and 4 h later. Patients were divided into four groups for analyses: SvO2 ≥ 60% at ICU admission and 4 h later; SvO2 ≥ 60% at admission but < 60% at 4 h; SvO2 < 60% at admission but ≥ 60% at 4 h; and SvO2 < 60% at both ICU admission and 4 h later. Kaplan–Meier survival curves, Cox regression models, and receiver operating characteristic curve analysis were used to assess differences among groups in 30-day and 1-year mortality. Results In the overall cohort, 52.9% underwent coronary artery bypass grafting (CABG), 29.1% valvular surgery, 12.1% combined CABG and valvular procedures, 3.5% surgery of the ascending aorta or aortic dissection, and 2.4% other cardiac surgery. The 1-year crude mortality was 4.3%. The best outcomes were associated with SvO2 ≥ 60% at both ICU admission and 4 h later. Hazard ratios for 1-year mortality were highest among patients with SvO2 < 60% at both ICU admission and 4 h later, regardless of surgical subgroup. Conclusion SvO2 values < 60% at ICU admission and 4 h after admission are associated with increased 30-day and 1-year mortality after cardiac surgery. Goal-directed therapy protocols targeting SvO2 ≥ 60% may be beneficial. Prospective studies are needed to confirm these observational findings.