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One of the problems of near-infrared-spectroscopy (NIRS) measurements is low reproducibility. The aim of the present study was to introduce quality criteria to increase reproducibility of peripheral NIRS measurements. In a prospective cohort study in 40 neonates, repeated NIRS measurements were performed on the calf. During five "reapplication" periods (of NIRS optodes), five "measurements" (venous occlusions) were performed. Tissue oxygenation index (TOI), mixed venous oxygenation (SvO2), fractional oxygen extraction (FOE), hemoglobin flow (Hbflow), oxygen delivery (DO2), and oxygen consumption (VO2) were assessed. Measurements with linear changes during venous occlusions were included for further analysis (first quality criterion: R(2)>0.95). The second quality criterion was the equation 0 < or = TOI-SvO2 < or = (SaO2-SvO2)x0.2. Variance components and mean standard deviations were analyzed after introduction of the quality criteria. Variance components of reapplication and measurement decreased after introduction of the second quality criterion (TOI: 46.6-35.0%, SvO2: 76.8-38.2%, FOE: 73.1-37.5%, Hbflow: 70.3-51.9%, DO2: 71.5-52.7%, and VO2: 70.9-63.8%). Mean standard deviations of TOI (6.6+/-3.0 to 4.7+/-3.2%), SvO2 (11.1+/-4.8 to 5.7+/-3.9%), FOE (11.3+/-4.8 to 5.9+/-4.0%), Hbflow (4.3+/-2.0 to 2.9+/-1.6 micromol100 mLmin), and DO2 (17.8+/-7.6 to 11.4+/-6.2 micromol100 mLmin) decreased significantly, too. Only 12% of measurements fulfilled both quality criteria. With the introduction of two quality criteria, test-retest variability of peripheral NIRS measurements decreased significantly and reproducibility increased significantly.

The aim of this study was to analyse changes in peripheral oxygenation in healthy term neonates within the first week of life with near-infrared spectroscopy and venous occlusion. Oxygen delivery did not change with increasing age. Oxygen consumption and fractional oxygen extraction increased, whereas tissue oxygenation index decreased with increasing age. N ear-infrared spectroscopy (NIRS), in combination with venous occlusion, enables measurements of peripheral oxygenation and perfusion. [1][2][3] In the present study, we carried out repeated measurements of peripheral oxygenation in healthy term neonates within the first week of life. The aim was to analyse changes in oxygen delivery (DO 2 ), oxygen consumption (VO 2 ), fractional oxygen extraction (FOE), tissue oxygenation index (TOI), mixed venous oxygenation (SvO 2 ), haemoglobin flow (Hbflow) and vascular resistance, to obtain normal values. METHODSNIRS measurements (NIRO 300, Hamamatsu Photonics, Shizuoka, Japan) and venous occlusions were carried out in each of 50 neonates twice within the first week of life. The local ethics committee approved the study.NIRS measures changes in oxygenated haemoglobin, deoxygenated haemoglobin, total haemoglobin and TOI. Measurements were carried out on neonates in the supine position during sleep after feeding. The two NIRS optodes were placed over the left forearm with a distance of 3.5 cm. Each measurement consisted of at least three venous occlusions lasting 20 s, without movement (artefacts), obtained with a pneumatic cuff placed around the upper arm.Heart rate and oxygen saturation (haemoglobin; SaO 2 ) were measured by pulse oximetry on the wrist. Central and peripheral temperatures were measured continuously. Mean arterial pressure (MAP) was measured before and after venous occlusions.Hbflow/min was calculated from the increase in total haemoglobin during the 20-s venous occlusion. Further parameters were calculated as follows: DO 2 = Hbflow646SaO 2 ; VO 2 = Hbflow646(SaO 2 2SvO 2 )where SvO 2 = oxygenated haemoglobin/total haemoglobin; FOE = DO 2 /VO 2 and vascular resistance = MAP6haemoglobin concentration/Hbflow. A blood sample was taken from each of 39 neonates within 24 h of the first measurement. VO 2 and DO 2 are measured in ml/kg/min. 4 Hbflow, DO 2 , VO 2 , FOE, TOI and SvO 2 for each neonate were determined as mean values of the three venous occlusions in each measurement. A paired t test was used for the comparison of the two measurements in each neonate. Vascular resistance was correlated with age and haemoglobin concentration to NIRS parameters by linear regression analysis. Data are mean (standard deviation (SD)). RESULTSThe 50 neonates (24 boys and 26 girls) had a mean age of 39.5 (SD 1

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