Near-infrared spectroscopy assesses cerebral tissue oxygen saturation (Scto2) based on the absorption spectra of oxygenated and deoxygenated hemoglobin. It has been reported that IV-administered dyes including methylene blue, indigo carmine, and indocyanine green (ICG) may cause falsely low-pulse oximetry readings (Spo2). Although methylene blue and indigo carmine may also decrease Scto2, the effect of ICG has not been documented.Methods:
Simultaneous changes in the heart rate, arterial blood pressure, Scto2, and Spo2 were measured after IV administration of ICG (12.5 mg diluted in 5.0 mL 0.9% NaCl) in 15 patients undergoing carotid endarterectomy under sevoflurane-remifentanil anesthesia.Results:
After the dye administration, no change in heart rate or arterial blood pressure was observed in any patient. Scto2 increased by 13.3±4.0 percentage points, reaching the peak at 42.0±28.4 seconds after the administration, whereas Spo2 decreased by 1.9±1.2 percentage points, reaching the peak at 64.0±42.5 seconds (P<0.0001 both).Conclusions:
ICG falsely increases the spectroscopy-determined cerebral oxygen saturation for up to 12 minutes but dampens pulse oximetry readings.