Tissue oxygen saturation during anaesthesia, cardiopulmonary bypass and intensive care stay for cardiac surgery

Introduction

Near-infrared spectroscopy is a novel method for rapid and noninvasive assessment of tissue oxygen saturation (StO₂). An association between StO₂ and oxygen delivery has been demonstrated during shock, trauma and resuscitation. We conducted a pilot observational study in which the aims were to measure changes in StO₂ during the perioperative period for scheduled cardiac surgery and to explore correlations between StO₂ and routine haemodynamic measures.

Methods

The study was approved by the UCLH Joint Research Ethics Committee. Written informed consent was gained from 74 patients undergoing scheduled coronary artery bypass grafting (CABG) and valvular surgery requiring cardiopulmonary bypass (CPB). The thenar eminence StO₂ was measured continuously during the perioperative period for a maximum of 24 hours using the InSpectra Tissue Spectrometer (Model 325; Hutchinson Technology Inc., USA). Haemodynamic variables were collected from patient records. The mean StO₂ was calculated for various time points within the study.

Results

The tissue spectrometer performed well throughout the study. From a baseline of 81.7% the StO₂ rose significantly during induction of anaesthesia to 88.5% (P < 0.001). Prior to and during CPB the StO₂ fell to a minimum of 77.6%, and rose significantly to 83.1% after CPB (P < 0.001). The mean StO₂ decreased during the ICU stay to a minimum of 70.0% at 2 hours post operation. There was marginal association between StO₂ measures and haemodynamic changes although all analyses resulted in areas under ROC curves <0.70.

Conclusion

The present study demonstrates interesting changes in tissue StO₂ during the perioperative period surrounding scheduled cardiac surgery. The trends suggest a fall in StO₂ throughout CPB and during early recovery in the ICU. Changes in StO₂ may reflect underlying tissue perfusion; therefore the utilisation of StO₂ as both an index for tissue hypoperfusion and as a therapeutic goal needs further exploration.