Skin pigmentation interferes with the clinical measurement of regional cerebral oxygen saturation

Devices utilizing near-infrared (NIR) spectroscopy have been used to assess regional intracerebral oxygen saturation (rSO2) during anaesthesia for a decade. The presence of wide differences among individuals reduces their applicability to steady-state measurements. Current devices may not adequately account for variations in skin pigmentation.

From our ongoing departmental registry, 3282 consecutive patients underwent cardiac surgery between 2010 and 2012 and their pre-induction measurements of rSO2 were available. Of these, 2096 identified themselves as Caucasian (Cauc) and 1186 as African-American (AA). Pre-induction rSO2, clinical and operative features were compared.

Clinical and operative details of these patients differed widely between the two populations. High-risk features were more common in AA patients, but no difference in mortality was observed (4.8% in AAs vs 4.7% in Caucs, P=0.87). Preprocedure rSO2 was systematically higher in Cauc (65.5% vs 53.3%, P<0.001). After multivariate linear regression adjustment, AA ethnicity proved to be associated independently with low rSO2 [odds ratio (OR) -8.28, 95% confidence interval (CI) -9.12 to -7.44, P<0.001]. Multivariate logistic regression analysis showed that preprocedural rSO2 was independently associated with operative mortality both in the Cauc group (OR 0.97, 95% CI 0.96-0.99, P=0.001) and in the AA group (OR 0.97, 95% CI 0.95-0.99, P=0.01).

AAs have a lower rSO2 than Caucs as measured by the INVOS 5100C cerebral oximeter. Reasonably, this could be attributed to attenuation of the NIR light by skin pigment. Despite this limitation, in both ethnic groups, lower preoperative rSO2 was predictive of greater operative mortality.