Influence of patient variables and sensor location on regional cerebral oxygen saturation measured by INVOS 4100 near-infrared spectrophotorneters

Cerebral oximeter based on near-infrared spectroscopy has been used as a continuous, noninvasive monitoring of regional cerebral oxygen saturation (rSo(2)). Although the absolute rSO(2) values have a wide range of variability, the factors affecting a variability of rSO(2) values have not been extensively investigated. The authors investigated the influence of patient variables and sensor location on rSO(2) measured by the cerebral oximeter INVOS 4100 in 111 patients anesthetized with sevoflurane, fentanyl, and nitrous oxide in oxygen. The sensors for rSO(2) measurements were applied on the right forehead (R), 1c lateral to R (R1), on the left forehead (L), 1 cm lateral to L (L1), and on the center of the forehead (C). The relationship between the rSO(2) values and patient variables were also analyzed. Values of rSO(2) at R1 and L1 were significantly lower than those at R and L, respectively. Values of rSO(2) at C were significantly higher compared with those at other sites. There were no significant correlations between the rSo(2) values and values of weight, height, and head size. Values of rSO(2) were similar between males and females. A significant negative correlation between the rSO(2) values and age and a positive correlation between the rSO(2) values and hemoglobin concentration were observed. These data indicate that patient age, hemoglobin concentration at the measurement, and sensor location can affect rSO(2) values.