Cerebral Oxygenation in Heart Surgery

Abstract

To the Editor: Recently, Murkin et al. (1) assessed brain oxygen saturation during coronary bypass surgery. With a simple protocol to optimize perfusion the authors conclude that monitoring cerebral oxygenation during a coronary bypass induces a significantly smaller incidence of major organ dysfunction postoperatively. The experience with using near-infra spectroscopy during coronary bypass is that immediately after the start of the heart lung machine some subjects exhibit a marked reduction in cerebral oxygenation, whereas in other subjects independently of cardiac index cerebral oxygenation is unchanged. However, the paper fails to address a few concerns important for interpretation of the data. First, the authors describe that if cardiac index was <2.0 L · m−2· min−1 the pump flow was increased to 2.5 L · m−2 · min−1. Therefore, was cardiac index similar in the two groups? Second, what was the pump flow value before it increased? Could it be that the significant difference in outcome between the two groups relate to that pump flow was too low in the control group? Certainly, the change in cerebral oxygenation in the two groups was almost nonsignificant and therefore the data opens for the question—do we need to record cerebral oxygenation? Rather than increased cerebral oxygenation was the effect of intervention related to increased inspired O2 fraction? With the vague conclusion that monitoring of cerebral oxygenation avoids organ dysfunction, it appears to be the same problem as with the Swan Gantz catheter. It may be a challenge to select the population in whom cerebral oxygenation needs to be optimized. Henning Bay Nielsen, MD, DMSci Jens Børglum, MD, MBA, PhD Department of Thoracic Anesthesia University of Copenhagen, Rigshospitalet Copenhagen, Denmark [email protected]