Do cerebral and somatic tissue oxygen saturation measurements correlate with each other during surgery?

Intraoperative maintenance of optimal tissue oxygenation is critical; however, it is uncertain whether measurements of different tissue beds correlate with each other. Cerebral tissue oxygen saturation (SctO₂) measured on the forehead and somatic tissue oxygen saturation (SstO₂) measured on limbs, using a tissue near-infrared spectroscopy, were simultaneously recorded every 2 s in patients having spine surgery or robotic hysterectomy. Simple linear regression was used to determine the static correlation between SctO₂ and SstO₂ using the median values of each min for each patient. The dynamic correlation between SctO₂ and SstO₂ was assessed by Pearson's correlation coefficient (CC) for each non-overlapping 2-min epoch. In patients having spine surgery (n = 99), SctO₂ and SstO₂ (mean ± SD) were 69.8 ± 4.9% and 75.5 ± 8.7%, whereas in patients having robotic hysterectomy (n = 106), the corresponding values were 74.9 ± 6.8% and 83.7 ± 6.2%. The static correlation between SctO₂ and SstO₂ was inconsistent (r ranging from - 0.86 to 0.93 in spine surgery and from - 0.74 to 0.85 in robotic hysterectomy). The proportional durations with CC ≤ - 0.3 (negative correlation), - 0.3 < CC < 0.3 (poor correlation) and CC ≥ 0.3 (positive correlation) were 18.3 ± 9.6%, 52.6 ± 12.1% and 29.0 ± 9.6%, respectively, in patients having spine surgery and 19.6 ± 9.0%, 58.6 ± 13.1% and 21.8 ± 8.0%, respectively, in patients having robotic hysterectomy. There are a large discrepancy and inconsistent correlation between intraoperative SctO₂ and SstO₂ measurements, suggesting their non-interchangeability.