A COMPARATIVE-STUDY OF 2 NEAR-INFRARED SPECTROPHOTOMETERS FOR THE ASSESSMENT OF CEREBRAL HEMODYNAMICS

Conventional near infrared spectroscopy (NIRS), introduced by Jobsis i n 1977, can be considered as a reliable trend monitor for cerebral oxy genation. Quantisation, however, is complex and cumbersome. Recently a relatively simple system for cerebral oximetry (INVOS 3100, Somanetic s Corporation, USA) was developed, measuring the regional oxygen satur ation (rSO(2)) in the capillary bed of the cerebrum, presented as a nu merical figure for easy interpretation. In this study a comparison was made between a conventional NIRS instrument and the new INVOS instrum ent, in order to obtain information about sensitivity and usefulness o f the INVOS system. Changes in cerebral haemodynamics were induced by a moderate decrease of the arterial oxygen saturation (SaO2) and by va rying the arterial carbon dioxide level (PaCO2). This will result in a higher (hypercapnia) or lower (hypocapnia) cerebral blood flow and su bsequent change of both NIRS signals and INVOS signal. Healthy volunte ers were used for this study. It was found that the steady state value for rSO(2) was 70 +/- 6% (mean +/- SD). During the lowering of arteri al saturation a poor correlation was found between rSO(2) and SaO2 (r= 0.47). Increased cerebral blood Row induced by hypercapnia was detecte d by both conventional NIRS and the INVOS. Decreased cerebral blood fl ow induced by hypocapnia could only be detected by conventional NIRS. It was concluded that due to the variation in displayed rSO(2) and the high amount of averaging in the algorithm the INVOS instrument does n ot yet provide more information than conventional NIRS.