Impact of transient decrease in mixed venous oxygen saturation on prognosis in off-pump coronary artery bypass surgery: a retrospective cohort study

BACKGROUND: The prognostic consequences of transient hemodynamic deterioration due to cardiac displacement, which is most severe during left circumflex artery (LCX) grafting in off-pump coronary artery bypass surgery (OPCAB) are unknown. This study aimed to investigate the association between mixed venous oxygen saturation (SvO(2)) < 60% during LCX grafting and the occurrence of composite of morbidity endpoints. METHODS: Data of patients who underwent elective OPCAB between January 2010 and December 2019 were reviewed. Logistic regression analysis was performed to detect risk factors for the composite of morbidity endpoints, defined as 30-day or in-hospital mortality, postoperative myocardial infarction, prolonged mechanical ventilation > 24 h, cerebrovascular accident, and acute kidney injury. RESULTS: Among 1,071 patients, the composite of morbidity endpoints occurred in 303 (28%) patients. SvO(2) < 60% during LCX grafting was significantly associated with the composite of morbidity (OR: 2.72, 95% CI [1.60, 4.61], P < 0.001) along with advanced age, chronic kidney disease, ratio of early mitral inflow velocity to mitral annular early diastolic velocity, and EuroSCORE II. Other major hemodynamic variables including the cardiac index were not associated with the outcome. Additional regression analysis revealed pre-operative anemia as a predictor of SvO(2) < 60% during LCX grafting (OR: 2.09, 95% CI [1.33, 3.29], P = 0.001). CONCLUSIONS: A decrease in SvO(2) < 60%, albeit confined to the period of cardiac displacement, was associated with a 2.7-fold increased risk of detrimental outcomes after OPCAB, implying the prognostic importance of this transient deterioration in oxygen supply-demand balance.