A validation method for near-infrared spectroscopy based tissue oximeters for cerebral and somatic tissue oxygen saturation measurements

Abstract

We describe the validation methodology for the NIRS based FORE-SIGHT ELITE® (CAS Medical Systems, Inc., Branford, CT, USA) tissue oximeter for cerebral and somatic tissue oxygen saturation (StO2) measurements for adult subjects submitted to the United States Food and Drug Administration (FDA) to obtain clearance for clinical use. This validation methodology evolved from a history of NIRS validations in the literature and FDA recommended use of Deming regression and bootstrapping statistical validation methods. For cerebral validation, forehead cerebral StO2 measurements were compared to a weighted 70:30 reference (REF CXB) of co-oximeter internal jugular venous and arterial blood saturation of healthy adult subjects during a controlled hypoxia sequence, with a sensor placed on the forehead. For somatic validation, somatic StO2 measurements were compared to a weighted 70:30 reference (REF CXS) of co-oximetry central venous and arterial saturation values following a similar protocol, with sensors place on the flank, quadriceps muscle, and calf muscle. With informed consent, 25 subjects successfully completed the cerebral validation study. The bias and precision (1 SD) of cerebral StO2 compared to REF CXB was −0.14 ± 3.07%. With informed consent, 24 subjects successfully completed the somatic validation study. The bias and precision of somatic StO2 compared to REF CXS was 0.04 ± 4.22% from the average of flank, quadriceps, and calf StO2 measurements to best represent the global whole body REF CXS. The NIRS validation methods presented potentially provide a reliable means to test NIRS monitors and qualify them for clinical use.

Comparison of tissue oximeters on a liquid phantom with adjustable optical properties: an extension

“…In our previous comparison studies in phantoms [38,[40][41][42] we observed substantial systematic differences between in vivo calibrated NIRS oximeters. Such differences were also shown in vivo [2][3][4][5][6][7][8] and are probably due to the error prone in vivo calibration rather than the simple nature of the phantom [20]. The oximeters included in [38] and here can be assumed to apply the multi-distance approach for calculation of StO 2 , since they provide more than one source-detector separation.…”

“…Some of the instruments used in [38] and this experiment were calibrated in vivo, which only probes a limited range of StO 2 safely [20,[43][44][45][46][47]. In neonates, however, StO 2 often lies and is considered outside this calibrated range.…”

“…A change in the group AVR assumption by 10 % (i.e. 20:80 % or 40:60 %) causes a change in bias of already ±3 % [20]. But a recent meta-analysis on published cerebral StO 2 acquired with the INVOS oximeter reported that even higher AVR of up to 75:25 % fit their data best [21].…”

“…The AVR is further influenced by e.g. the end tidal CO 2 , which must be kept constant [20] and the subject's positioning [2] which may cause systematic differences between studies. A change in the group AVR assumption by 10 % (i.e.…”

Somatic tissue oxygenation monitoring

“…Although this might be true of most commercial NIRS devices, the FORE-SIGHT ELITE, (CASMED, Inc., Branford, Connecticut, USA) monitor used in our study 3 features an algorithm specifically developed for muscle and validated for large muscle tissue applications using a universal sensor design. 4 There is emerging evidence that Smt O 2 might provide an early and reliable non-invasive indicator of insufficient global tissue perfusion as reflected by muscle, colon, and brain metabolomics. 5 This provides a potential alternative to more invasive monitors of tissue oxygen tension.…”