Abstract
In a blood-lipid liquid phantom the prototype near-infrared spectroscopy oximeter OxyPrem was calibrated against the INVOS® 5100c adult sensor in respect to values of regional tissue oxygen haemoglobin saturation (rStO2) for possible inclusion in the randomised clinical trial - SafeBoosC. In addition different commercial NIRS oximeters were compared on changing haemoglobin oxygen saturation and compared against co-oximetry. The best calibration was achieved with a simple offset and a linear scaling of the OxyPrem rStO2 values. The INVOS adult and pediatric sensor gave systematically different values, while the difference between the NIRO® 300 and the two INVOS sensors were magnitude dependent. The co-oximetry proved unreliable on such low haemoglobin and high Intralipid levels.
Highlights
Near infrared spectroscopy (NIRS) enables non-invasive measurement of the regional tissue oxygen haemoglobin saturation. rStO2 is correlated to both arterial (SaO2) and venous oxygen haemoglobin saturation (SvO2) [1] and is an estimate of the local oxygen balance, i.e. the oxygen delivery - oxygen consumption difference
The INVOS adult and pediatric SomaSensors were linearly correlated with the pediatric sensor reading systematically higher than the adult sensor (y = 0.96x + 17.91; Rsquare 0.99)
The INVOS adult SomaSensor was linearly correlated with the NIRO, but with a different slope (y = 0.53x + 30.45; R-square 0.98) (Fig. 5)
Summary
Near infrared spectroscopy (NIRS) enables non-invasive measurement of the regional tissue oxygen haemoglobin saturation (rStO2). rStO2 is correlated to both arterial (SaO2) and venous oxygen haemoglobin saturation (SvO2) [1] and is an estimate of the local oxygen balance, i.e. the oxygen delivery - oxygen consumption difference. RStO2 is correlated to both arterial (SaO2) and venous oxygen haemoglobin saturation (SvO2) [1] and is an estimate of the local oxygen balance, i.e. the oxygen delivery - oxygen consumption difference. In-vivo it is usually validated by comparison of rStO2 with a weighted mean of SaO2 and SvO2 [4,5,6,7,8,9,10]. This method has limitations as it includes the imprecision of NIRS re-siting, the errors of measurement on SaO2 and SvO2, as well as extra-cerebral contribution to jugular venous blood. In-vitro testing on solid state or liquid phantoms has the advantage of controllable optical properties and less variation [11,12]
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