The influence of the timing of cord clamping on postnatal cerebral oxygenation in preterm neonates: a randomized, controlled trial.

OBJECTIVE: Our goal was to investigate the effect of placentofetal transfusion on cerebral oxygenation in preterm infants by near-infrared spectroscopy. SUBJECTS: A total of 39 preterm infants with a median gestational age of 30.4 weeks were randomly assigned to an experiment group (n = 15) and a control group (n = 24). INTERVENTIONS: The delivery of the infants in the experiment group was immediately followed by maternal administration of syntocinon, the infant was placed 15 cm below the placenta, and cord clamping was delayed by 60 to 90 seconds. The infants in the control group were delivered conventionally. At the ages of 4 and 24 hours, cerebral hemoglobin concentrations, cerebral blood volume, and regional tissue oxygenation were measured by near-infrared spectroscopy. RESULTS: Cerebral blood volume was not different between the 2 groups at the age of 4 hours (6.1 vs 5.8 mL/100 g of tissue) nor at the age of 24 hours (6.2 vs 6.2 mL/100 g of tissue). Mean regional tissue oxygenation of the experiment group was higher at the ages of 4 hours (69.9% vs 65.5%) and of 24 hours (71.3% vs 68.1%). CONCLUSION: Delayed clamping of the umbilical cord improves cerebral oxygenation in preterm infants in the first 24 hours.

Variability of cerebral hemoglobin concentration in very preterm infants during the first 6 hours of life.

Cerebral hemoglobin concentration (cHbc), a major determinant of oxygen transport capacity in the brain, shows a considerable variability due to physiological and methodological factors. In order to determine the (relative) contribution of these factors, the cHbc variability within the first 6 hours of life was studied in 28 very preterm infants using near infrared spectrophotometry (NIRS). Mean cHbc values were 46.4 +/- 14.1 micromol/l (2.75 +/- 0.84 ml/100 g). Is the variability in cHbc related to the methodology of cHbc measurements or to physiological variables? A statistical model of stepwise regression (backward selection) with 13 independent variables and with cHbc as a dependent variable showed that, from the total variability of +/- 14.1 micromol/l, only 3.7 micromol/l (26%) were of methodological origin, while the major portion, 9.3 micromol/l (66%) were related to four physiological variables: birth weight, gestational age, blood glucose and transcutaneous carbon dioxide tension. The remaining 1.1 micromol/l (7.8%) were unexplained. We conclude that NIRS, which allows continuous monitoring of cerebral oxygenation and metabolism even in the first hours of postnatal life, is a valid technique to measure cHbc in very preterm infants. The major portion of the large variability of early cHbc registrations can be attributed to physiological factors.

The influence of a clear layer on near infrared spectrophotometry: comparison of measurements in a liquid neonatal head phantom to infants in vivo.

Near infrared spectrophotometric (NIRS) algorithms to determine the tissue oxygen saturation (TOI) assume a semi-infinite, homogenous tissue geometry. At the head, the clear cerebrospinal fluid (CSF) layer may violate this assumption. The aim was to estimate the error in the TOI values caused by the CSF layer in vitro and to confirm the results in vivo. The liquid phantom mimicking the neonatal head, consisted of a spherical shell of silicone filled with a liquid solution (1% Intralipid, 60 mumol/l haemoglobin, yeast) and a clear layer imitating CSF. The solution was oxygenated and deoxygenated, while measuring its TOI and pO2. Without clear layer the mean TOI was 90.9 +/- 0.5% at pO2 > 18 kPa and decreased to 26.0 +/- 1.3% at pO2 = 0 kPa. With a clear layer the TOI increased from 27.8 +/- 0.8% at pO2 > 18 kPa to 68.0 +/- 0.8% at pO2 = 0 kPa. The clear layer caused a large error in the TOI. In ten mechanically ventilated infants (postnatal age 0.03 to 8 months) the TOI (at the head) and arterial oxygen saturation (SaO2) were measured while the inspired oxygen fraction was altered. The TOI was always positively correlated with the SaO2 (mean slope linear regression = 0.89, r2 = 0.62). Thus an adverse effect of the CSF layer on TOI measurements can be excluded for infants. The CSF layer is not modelled correctly in the phantom.

Comparison of three methods to measure absolute cerebral hemoglobin concentration in neonates by near-infrared spectrophotometry.

Three methods by which to determine absolute total cerebral hemoglobin concentration (tHb in micromol/L) by near-infrared spectrophotometry (NIRS) have evolved: (1) tHbo, requiring oxygenation changes and arterial oxygen saturation measurements as a reference using a relative NIRS algorithm, (2) tHbg, using a geometrical multidistance principle and (3) tHbgo, a combination of both. The aim of this study was to compare the three methods quantitatively. Sixteen clinically stable preterm infants with a mean gestational age of 29.6 (range of 25.1-36.4) weeks, birthweight of 1386 (680-2820) g and a postnatal age of 2.5 (0.5-6) days, who needed supplemental oxygen, were enrolled. The mean+/-standard deviation tHbg was 150.2+/-41.8 micromol/L (range of 61.6-228.9 micromol/L), the tHbo was 62.1+/-27.2 micromol/L (26.0-110.8 micromol/L) and the tHbgo was 89.3+/-45.6 micromol/L (26.5-195.9 micromol/L). The correlation coefficient among the three methods were tHbg and tHbgo r=0.736; tHbo and tHbgo r=0.938; tHbg and tHbo r=0.598. A multiple regression with variable selection by Mellow's C(p) showed, that tHbg was correlated to the birthweight, the postnatal age, the heart rate and the pCO2 (r(2)=0.588), tHbo and tHbgo were associated with the hemoglobin concentration in the blood, the mean arterial blood pressure and the pCO2 (r(2)=0.493 and 0.406, respectively). The three methods (tHbg, tHbo, and tHbgo) give systematically different tHb readings and large intersubject variability.