Adjusted Relationships between Mean Arterial Pressure, Cardiac Index, and Tissue Oxygenation during Off-pump Coronary...

Tissue oxygenation measured by near-infrared spectroscopy can guide hemodynamic management, yet the joint association of mean arterial pressure (MAP) and cardiac index with tissue oxygenation, and the conditional association of each at fixed levels of the other, remain incompletely defined.

The authors analyzed intraoperative 1-Hz signals from patients undergoing off-pump coronary artery bypass surgery. Synchronized MAP, cardiac index, cerebral tissue oxygenation saturation (SctO 2 ), and forearm tissue oxygenation saturation (SftO 2 ) were modeled using generalized additive models. Two-dimensional smoothing over MAP-cardiac index estimated surfaces and two-dimensional slices characterized conditional relationships. Covariates were prespecified. Bootstrap quantified uncertainty and 95% CI. The authors emphasized estimation and visualization.

Analytic cohorts included 1,864 patients for left SctO 2 , 1,863 for right SctO 2 , and 1,860 for SftO 2 , each with more than 20 million eligible observations. Adjusted surfaces characterized mean tissue oxygenation across combinations of MAP and cardiac index. Two-dimensional slices showed that SctO 2 depended on both MAP and cardiac index. The MAP-SctO 2 relationship showed a substantial reduction in slope over a MAP range of 70 to 100 mmHg, mimicking cerebral pressure autoregulation. SctO 2 increased as cardiac index rose, reached its highest level at approximately 4.2 l · min -1 · m -2 , and then plateaued or slightly decreased at higher cardiac index. SftO 2 was sensitive to cardiac index, not MAP; it increased most steeply at cardiac index 2.8 l · min -1 · m -2 or less, showed a reduced slope over the cardiac index range of 2.8 to 4.2 l · min -1 · m -2 , and continued to increase at higher cardiac index. These patterns were more prominent in younger patients, females, and those with a baseline blood pressure less than 140/90 mmHg.

During off-pump coronary artery bypass surgery, cerebral oxygenation was sensitive to both pressure and flow, whereas forearm oxygenation primarily tracked flow. Reductions in slope across specific pressure and flow ranges may reflect physiologic regulation but should not be interpreted as evidence for treatment targets or practice-changing interventions.