Reoperative adult cardiac surgery represents one of the highest-risk categories in contemporary cardiothoracic practice. Despite advancements in surgical technique, anesthesia, and perfusion management, patients undergoing redo cardiac procedures continue to face substantial perioperative morbidity and mortality. In this important retrospective cohort study published in the Journal of Cardiothoracic and Vascular Anesthesia, Rubino and colleagues evaluated whether indexed oxygen delivery (DO₂i) during cardiopulmonary bypass (CPB) independently predicts in-hospital mortality and postoperative complications in reoperative cardiac surgery patients .
Study Design and Population
The investigators analyzed 343 adult patients who underwent reoperative cardiac surgery between 2011 and 2021 at a tertiary academic center. Exclusion criteria eliminated confounding high-risk conditions such as aortic dissection, deep hypothermic circulatory arrest, ventricular assist device implantation, transplantation, and emergency surgery. The cohort represented a complex population: 58% were anemic at baseline, nearly one-third had chronic kidney disease, and the median EuroSCORE II predicted mortality risk was 6.1%.
The primary objective was to evaluate whether intraoperative DO₂i during CPB was associated with in-hospital mortality. Secondary outcomes included acute kidney injury (AKI), cardiac morbidity (including high-dose inotropes, intra-aortic balloon pump, or extracorporeal membrane oxygenation), prolonged mechanical ventilation, and neurologic complications.
Oxygen Delivery During Cardiopulmonary Bypass
During CPB, systemic oxygen delivery becomes entirely dependent on extracorporeal circulation. DO₂i reflects pump flow and arterial oxygen content, making it a critical determinant of tissue perfusion. Institutional protocols targeted a DO₂i of at least 260 mL/min/m².
The median DO₂i observed was 300.8 ± 52.3 mL/min/m². Using receiver operating characteristic curve analysis (shown in Figure 1 on page 3), the authors identified a threshold of 289.4 mL/min/m² as the optimal discriminator for in-hospital mortality (AUC 0.756; sensitivity 78%; specificity 64%). This threshold became the defining cutoff for risk stratification.
Key Findings: Mortality and Morbidity
In-hospital mortality was 14.6%. Multivariable logistic regression demonstrated that each 1 mL/min/m² decrease in DO₂i increased mortality risk by 1.6% (OR 1.016). More strikingly, a median DO₂i below 289.4 mL/min/m² was associated with a fourfold increase in mortality (OR 4.119).
Patients with lower DO₂i had significantly worse outcomes:
- In-hospital mortality: 26.8% vs 6.0% (unadjusted)
- AKI incidence: 53.6% overall, significantly higher in low DO₂i group
- Cardiac morbidity: 42.3% overall, markedly increased in low DO₂i patients
- Prolonged mechanical ventilation: significantly more frequent
- Greater transfusion requirements and longer CPB duration
After inverse probability of treatment weighting (IPTW) to balance baseline risk profiles, low DO₂i remained independently associated with adverse outcomes. The weighted mortality rates were 21.6% versus 6.6% (p < 0.001). The doubly robust analysis estimated an absolute 15.1% increase in postoperative mortality for patients exposed to low oxygen delivery.
The propensity-adjusted multivariable model (Figure 2 on page 6) confirmed DO₂i as an independent predictor, even after adjusting for established risk factors including left ventricular ejection fraction, diabetes, anemia, urgency, EuroSCORE II, CPB duration, and transfusion burden.
Pathophysiologic Implications
These findings reinforce the concept that inadequate oxygen delivery during CPB induces systemic hypoxic stress rather than isolated renal injury. While previous landmark studies focused primarily on AKI thresholds around 262–272 mL/min/m², this study identified a slightly higher mortality-associated threshold near 289–298 mL/min/m² in a high-risk redo population.
Reoperative cardiac surgery patients are particularly vulnerable due to prolonged operative times, increased inflammatory response, technical complexity, and higher transfusion requirements. Nearly 30% of patients in this cohort experienced CPB times exceeding 180 minutes, compounding exposure to potential hypoperfusion.
Importantly, the study also acknowledges the potential harms of hyperoxia, referencing emerging evidence that excessive oxygen exposure may worsen oxidative stress and inflammatory injury. Thus, the goal is not simply maximal oxygenation, but optimized and individualized oxygen delivery.
Clinical Implications
This research supports a paradigm shift toward goal-directed perfusion strategies in cardiac surgery. Continuous DO₂i monitoring and protocolized adjustments in pump flow, hemoglobin concentration, and perfusion parameters could become central to improving outcomes in high-risk patients.
Rather than focusing solely on mean arterial pressure or hemoglobin nadir, integrating DO₂i into routine CPB management may allow perfusionists and surgeons to proactively prevent tissue hypoxia. In redo cardiac surgery—where mortality remains substantial—this approach could offer a modifiable intraoperative target.
Study Limitations
The authors appropriately note several limitations. DO₂i was not continuously recorded; instead, median values during cross-clamp time were used. The retrospective single-center design introduces potential bias. Additionally, postoperative outcomes are multifactorial, and DO₂i alone cannot explain all observed differences.
Nonetheless, robust statistical methods—including IPTW and doubly robust modeling—strengthen the validity of the conclusions.
Conclusion
This study provides compelling evidence that low indexed oxygen delivery during cardiopulmonary bypass is a powerful independent predictor of in-hospital mortality and major morbidity in reoperative adult cardiac surgery patients. A median DO₂i below approximately 289 mL/min/m² was associated with significantly increased mortality, acute kidney injury, cardiac complications, and prolonged ventilation.
These findings underscore the importance of individualized oxygen delivery optimization during CPB and suggest that DO₂i-guided perfusion strategies may represent an important advancement in improving survival and organ protection in high-risk cardiac surgery.
