574 Near-Infrared-Spectroscopy to Determine Cerebral Oxygenation in Neonates: Do Absorption and Scattering Coefficients Correlate with Skin, Bone, and Cerebrospinalfluid Thickness?

Abstract

Background: Taking into account both the attenuation of light and the phase-shift, frequency domain near-infrared-spectroscopy (FD-) NIRS enables to measure the absolute scattering (µs') and absorption (µa) coefficients of tissue. Aim: To evaluate the effect of skin, bone, and cerebrospinalfluid thickness on µa and µs'. Methods: The Oxiplex TS (ISS Inc., Champaign, IL, USA) FD-NIRS and proprietary data analysis software were used in clinically stable neonates: gestational age 34 (30 4/7-39 6/7) [weeks], postnatal age 11 (1-45) [days], weight 2,810 (2,650-3,860) [g]. The optode was placed over the right temporoparietal- region and four measurements of at least 2 minutes each were performed per subject at 1Hz sampling rate. To determine the thickness of the tissues, cranial ultrasound was performed (Toshiba Aplio, applying a 7-14MHz longitudinal transducer). All data are median (min.-max.). Results: For all patients µs' and µa at 692nm were 7.92(4.55-8.92)cm-1 and 0.086(0.076-0.1345) cm-1, and at 834nm were 6.20(3.67-7.51)cm-1 and 0.102(0.090-0.135)cm-1. Skin thickness was 1,5(1.1-1,7)mm, bone thickness was 2,9(2,6-2,3) mm and cerebrospinalfluid thickness was 3,1(2,4- 3,7)mm. In univariate linear regression analysis µa correlated negatively with skin thickness (692nm: r2=0.91; 834nm: r2=0.74), and to a lesser extend with cerebrospinalfluid thickness. µs' correlated positively with bone thickness (692nm: r2=0.49; 834nm: r2=0.79). Conclusion: Skin, bone, and cerebrospinalfluid thickness were correlated with µs' and µa. It is unclear whether this correlation is causal or confounding and if it affects the accuracy of NIRS measurements.