The Noninvasive Measurement of Absolute Cerebral Deoxyhemoglobin Concentration and Mean Optical Path Length in the Neonatal Brain by Second Derivative Near Infrared Spectroscopy

Abstract

We have used second differential near infrared spectroscopy of water to determine the mean optical path length of the neonatal brain. By obtaining the ratio of the second differential features of deoxyhemoglobin to those of water, the absolute cerebral concentration of deoxyhemoglobin can be monitored continuously and noninvasively. Nineteen neonates were studied; the gestational age at birth varied from 23 to 38 wk, and the postconceptual age, when the spectra were recorded, ranged from 35 to 48 wk. The calculated mean deoxyhemoglobin concentration was 14.6 +/- 4.0 microM; the differential path length factor (mean optical path length/optode separation) calculated from the water peak at 730 nm was 4.66 +/- 1.01, and that calculated at the 830-nm peak was 3.91 +/- 0.75. These values are consistent with path length measurements using laser time-of-flight spectroscopy on postmortem neonates and phase-resolved spectroscopy on live neonates. Induced arterial oxygen saturation decreases from 98 to 93% showed no significant change in the mean optical path length, despite significant cerebral desaturation. Changes in the deoxyhemoglobin concentration after this procedure were identical, whether measured by second differential analysis at 760 nm or by multilinear regression over the wavelength range 740-900 nm. When combined with existing methods of measuring total cerebral hemoglobin concentration, second differential near infrared spectroscopy can be used to derive the mean cerebral oxygen saturation. A preliminary experiment outlined the feasibility of this approach and yielded a saturation value of 63%, consistent with near infrared sampling of a predominantly venous pool in the brain.

Measurement of Cerebral Oxidative Metabolism with Near-Infrared Spectroscopy: A Validation Study

“…Measuring reduced CMRO 2 may be one method for predicting the early onset of hypoxic-ischemic brain damage (Hagberg, 2004). Because of recent advances in hemodynamic measurements (Springett et al, 2001;Brown et al, 2002) and in the quantification of NIR chromophores in vivo (Matcher et al, 1994;Cooper et al, 1996), NIRS has the potential to offer a safe and rapid approach for quantitatively measuring CMRO 2 in newborns. In the present study, we found excellent agreement within a range of approximately 1.5 to 4.0 mL O 2 /mins per 100 g between our NIRS-based measurements of CMRO 2 and concurrent measurements of CMRO 2 obtained from arterial and sagittal sinus blood samples.…”

“…In the present study, the second derivative technique was applied to continuous wave data to account for scatter (Matcher et al, 1994). Real-time measurements of the differential pathlength were acquired using the known water concentration in brain (85%) (Cooper et al, 1996). A consequence of the second derivative approach is that the AVDO 2 must be calculated solely from the tissue [Hb] as the second derivative of the HbO 2 absorption spectrum is relatively featureless.…”

“…This is a reasonable assumption with regards to piglets and human neonates as their skulls are relatively thin, but a poor assumption with regards to adults (Cooper et al, 1996). It has been shown that over 50% of the illuminated tissue volume in adults can be comprised of extra-cerebral tissue (Steinbrink et al, 2001).…”

“…Using the second derivative technique described by Matcher et al (1994) to account for scatter and assuming a water concentration of 85% (Cooper et al, 1996), the DPF and absolute concentrations of endogenous absorbers-as opposed to absolute changes of concentrations-can be obtained in real time.…”

Comparison of Cerebral Oximeter and Pulse Oximeter Values in the first 72 hours in Premature, Asphyctic and Healthy Newborns

“…Cerebral oximeter is a non-invasive optic technique based on NIRS which allows continuous and synchronous monitoring of the oxygen saturation of cerebral tissue (7,9,10). Cerebral oximeter is a promising modality in neonatal intensive care units (11).…”