Cerebral oximetry

Two near-infrared spectroscopy (NIRS) devices were compared with regard to their responses to changes in cerebral hemoglobin oxygenation induced by hy poxia and hypercapnia in five healthy volunteers. Sensors belonging to each NIRS device were placed on opposite sides of the volunteer's forehead. The INVOS-3100A device, approved by the United States Food and Drug Administration, records the percentage of oxyhemoglobin (HbO (2)) saturation and the investigational NIRO500 device records absolute cha nges in HbO(2), deoxyhemoglobin, and total hemoglobin in micromolar concent rations referenced to an arbitrary baseline. The Volunteers breathed separa te mixtures of 7% CO2 in O-2 and 10% O-2 for 5 minutes in random order. Art erial blood pressure, end-tidal CO2 (ETCO2) arterial O-2 saturation, and el ectrocardiographic data were continuously monitored. Hypercapnia increased (p < 0.01) ETCO2 from 42 +/- 2 to 56 +/- 3 mm Hg (mea n +/- standard deviation), resulting in a 7.3 +/- 0.2% in crease (p < 0.005 ) in cerebral HbO(2) saturation detected by the INVOS3100A device and an 11 .6 +/- 3 muM increase (p < 0.0008) in HbO(2) detected by the NIRO500. Hypox ia decreased (p < 0.01) arterial HbO(2) saturation from 98 +/- 1 to 87 +/- 3%, causing a 5.1 +/- 1.2% decrease (p < 0.01) in the percentage of HbO(2) saturation detected by the INVOS3100A device and a 9.7 +/- 6.3 <mu>M decrea se in HbO(2) detected by the NIRO500. The responses of the NIRO500 and the INVOS3100A instruments to changes in c erebral oxygenation resulting from hypercapnia and hypoxia were generally s imilar; however, responses tended to be greater when recorded by the NIRO50 0 device, perhaps because, unlike the INVOS3100A device, the NIRO500 does n ot correct for skin and bone contamination.