Extracranial contamination in the INVOS 5100C versus the FORE-SIGHT ELITE cerebral oximeter: a prospective...

Previous studies have found that most cerebral oximeters are subject to inaccuracies secondary to extracranial contamination of the cerebral oximetric signals. We hypothesized that the more advanced second-generation FORE-SIGHT ELITE cerebral oximeter would be significantly less affected by extracranial tissue hypoxemia than the more widely used first-generation INVOS™ 5100C monitor.

Twenty healthy volunteers aged 18-45 yr had the INVOS and FORE-SIGHT probes placed on their forehead in a random sequence while in the supine position. A pneumatic head cuff was then placed around each volunteer's head just below both the oximeter and a concomitantly placed scalp forehead pulse oximeter probe. The subjects' scalp cerebral oxygen saturation (SctO2) values were measured and compared using the two different devices in sequence, both before and after scalp tissue ischemia was induced by the pneumatic cuff.

Extracranial ischemia resulted in a significant reduction in SctO2 values from baseline in both devices. The INVOS 5100C recorded a median [interquartile range] decrease in SctO2 from baseline at five minutes of 15.1% [12.6 - 17.6], while that recorded by the FORESIGHT ELITE device was 8.6% [4.0 -12.3] at five minutes (median difference, 7.9%; 99% confidence interval, 1.9 to 16.5; P = 0.002).

Updated technological algorithms employed in the FORE-SIGHT ELITE cerebral oximeter may be responsible for less extracranial contamination than was observed in the previous-generation INVOS 5100C device. The impact that this extracranial contamination may have on the clinical use of these devices remains to be determined.