A comparison of the monitors INVOS3100 and NIRO500 in detecting changes incerebral oxygenation

Background: Measurements of cerebral haemoglobin oxygenation of 2 near-infr ared spectroscopy devices (INVOS 3100 and NIRO 500) were compared during an d after hypocapnia. Methods: Fifteen awake, healthy volunteers, who hyperventilated to obtain e nd-tidal CO2 (EtCO2) values of approximately 20 mmHg, were studied. During hyperventilation and 8 min thereafter, EtCO2, INVOS 3100 (RSO2=regional cer ebral oxygenation) and NIRO 500 recordings (HbO(2)=oxyhaemoglobin, Hb= deox yhaemoglobin, Hb-diff=HbO(2)-Hb CtO(2)=oxidised cytochrome oxidase aa3) wer e analysed. Results: Hyperventilation induced a significant decline in EtCO2 from 30.5 to 14.7 mmHg (P<0.001) and RSO2 from 67.1% to 62.7% (P=0.025). At hypocapni a, only Hb (+1.61+/-0.48 mu mol/L; P<0.001) and Hb-diff (-3.01+/-2.0 mu mol /L; P<0.001) indicated a decline in cerebral haemoglobin oxygenation. Withi n 8 min after hyperventilation, both EtCO2 and RSO2 normalised to values in significantly different from baseline. In contrast, Hb and Hb-diff remained significantly different (Hb: +2.52+/-1.28 mu mol/l; P<0.001, Hb-diff: -4.3 1+/-4.0 mu mol/L; P<0.001). A correlation with EtCO2 was found for RSO2 (R= 0.35; P<0.001) and CtO(2) (R=0.42; P<0.001). AU volunteers were continuousl y awake and none presented clinical symptoms of cerebral hypoxia. Conclusion: Changes in cerebral haemoglobin oxygenation state were reflecte d more accurately by INVOS 3100 than NIRO 500. The cause may be the differe nt technology of the monitors, since INVOS 3100 eliminates the contribution of extracranial oxygenation.