Extracranial contamination in the INVOS 5100C versus the FORE-SIGHT ELITE cerebral oximeter: a prospective observational crossover study in volunteers

Purpose: 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. Methods: 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. Results: 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). Conclusion: 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.