Cerebral tissue oximetry by near-infrared spectroscopy (NIRS) is a growing monitoring modality during surgery and intensive care. Accumulating evidence suggest that cerebral NIRS could have prognostic value [1
], however clinical utility remains to be proven. Concerns have been raised about the validity and precision of the technology [3
]. Here we introduce a practical method to compare the most important characteristics of tissue oximetry and apply it to 3 commercial NIRS instruments and a prototype.
The preterm infant is born in a state of hemodynamic instability hence reliable absolute values are needed. The values of regional tissue hemoglobin saturation (StO2
) from different cerebral oximeters are correlated [5
], but the absolute values differ systematically. Dullenkopf et al. found that there was a mean difference of 11.3% ± 5.4 and 13.8 ± 7.9, when the pediatric sensor of INVOS 5100 was compared to the adult sensor and the NIRO 300, respectively [6
]. Furthermore, poor reproducibility is an important concern when applying NIRS in a clinical setting [4
]. Using NIRO 300, the within-infant standard deviation (Sw
) was 5.2% with repeated cerebral measurements in preterm newborns [7
].Using a different instrument, Critikon 2020, the Sw
was only 1.7% on the neonatal head [8
], but this instrument also underestimated changes in concentration of hemoglobin [9
]. Thus in order to assess a instrument for clinical use the absolute StO2
values, reproducibility, and dynamic range need to be tested.
This study presents the first step in a series of studies of NIRS oximeters. While clinical research in neonatology is difficult and test of dynamic range impossible other methods of testing are needed. Our overall goal is to facilitate the process of collecting good evidence of the benefits and harms of cerebral oximetry. Knowledge of the instruments is important. We chose three different continuous wave instruments, that have previously been used in neonatal studies: INVOS 5100 (Somanetics, Troy, Michigan, USA), NIRO 300 and NIRO 200 NX (Hamamatsu Phototonics, Hamamatsu City, Japan) [10
] and the prototype OxyPrem (Biomedical Optic Research Laboratory, Zurich, Switzerland)—a newly developed instrument for neonates.
We propose a simple and practical setup to test and compare the absolute values, reproducibility, and dynamic range of StO2 by different instruments. This has to our knowledge not been done before. As these instruments use different source-detector separations from 2 to 4 cm, we also studied the effect different source-detector separations with the NIRO 200 NX. All measurements were done on the forearm of healthy adults.