Background:

Adequate organ perfusion during cardiopulmonary bypass (CPB) requires accurate estimation and adjustment of flow rates which conventional methods may not always achieve. Perioperative monitoring of cerebral oxygen saturation (ScO₂) may detect changes in oxygen transport. This study aims to compare estimated and measured perfusion flow rates and assess the capacity of ScO₂ to detect subtle changes in oxygen transport during CPB.

Methods:

This observational study included 50 patients scheduled for elective coronary artery bypass grafting (CABG) surgery, all of whom provided written informed consent. Perfusion flow rates were estimated using the DuBois formula and measured using echocardiography and a flow probe in the arterial line of the CPB system. ScO₂ was continuously monitored, alongside intermittent measurements of oxygen delivery and extraction ratios.

Results:

Significant discrepancies were found between estimated flow rates (5.2 [4.8–5.5] L/min) and those measured at the start of the surgery (4.6 [4.0–5.0] L/min). These discrepancies were flow rate-dependent, being more pronounced at lower perfusion rates and diminishing as rates increased. Furthermore, ScO₂ showed a consistent correlation with both oxygen delivery (r = 0.48) and oxygen extraction ratio (r = 0.45).

Conclusions:

This study highlights discrepancies between estimated and actual perfusion flow rates during CPB and underscores the value of ScO₂ monitoring as a continuous, noninvasive tool for maintaining adequate organ perfusion, suggesting a need for improved, patient-tailored perfusion strategies.