# Cerebral Oxygen Saturation Associates with Changes in Oxygen Transport Parameters during Cardiopulmonary Bypass

## TL;DR

This study shows that cerebral oxygen saturation can detect changes in oxygen transport during heart surgery, highlighting issues with estimated versus actual blood flow rates.

## Contribution

The study demonstrates that cerebral oxygen saturation correlates with oxygen delivery and extraction during cardiopulmonary bypass, suggesting its potential for real-time perfusion monitoring.

## Key findings

- Estimated flow rates were higher than measured rates at the start of surgery.
- Discrepancies between estimated and measured flow rates were more significant at lower perfusion rates.
- Cerebral oxygen saturation correlated with oxygen delivery and extraction ratios.

## Abstract

(1) 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. (2) 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. (3) 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). (4) 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.