Unresponsive Low Mixed Venous Oxygen Saturation During Early Intensive Care Unit Stay is Associated With Increased Risk of Organ Dysfunction After Cardiac Surgery: A Single-Center Retrospective Study

Objectives: The aim of the study was to determine if unresponsive mixed venous oxygen saturation (SvO₂) values during early postoperative hours are associated with postoperative organ dysfunction.

Design: A single-center retrospective observational study.

Setting: A university hospital.

Participants: A total of 6,282 adult patients requiring cardiac surgery who underwent surgery in a University Hospital from 2007 to 2020.

Interventions: A pulmonary artery catheter was used to gather SvO₂ samples after surgery at admission to the intensive care unit (ICU) and 4 hours later. For the analysis, patients were divided into 4 groups according to their SvO₂ values. The rate of organ dysfunctions categorized according to the SOFA score was then studied among these subgroups.

Measurements and main results: The crude mortality rate for the cohort at 1 year was 4.3%. Multiple organ dysfunction syndrome (MODS) was present in 33.0% of patients in the early postoperative phase. During the 4-hour initial treatment period, 43% of the 931 patients with low SvO₂ on admission responded to goal-directed therapy to increase SvO₂ >60%; whereas, in 57% of the 931 patients, the low SvO₂ was sustained. According to the adjusted logistic regression analyses, the odds ratio for MODS (4.23 [95% CI 3.41-5.25]), renal- replacement therapy (4.97 [95% CI 3.28-7.52]), time on a ventilator (2.34 [95% CI 2.17-2.52]), and vasoactive-inotropic score >30 (3.62 [95% CI 2.96-4.43]) were the highest in the group with sustained low SvO₂.

Conclusions: Patients with SvO₂ <60% at ICU admission and 4 hours later had the greatest risk of postoperative MODS. Responsiveness to a goal-directed therapy protocol targeting maintaining or increasing SvO₂ ≥60% at and after ICU admission may be beneficial.