Orthogonal polarization spectral imaging (OPS): a novel method to measure the microcirculation in term and preterm infants transcutaneously.

Little is known about the microvascular perfusion of the skin postnatally. Skin microvascular parameters can be assessed noninvasively with orthogonal polarization spectral imaging (OPS), a technique where, through the use of special optics, a virtual light source is created at a depth of 1 mm within the tissue. The light is absorbed by the Hb, yielding an image of the illuminated Hb-carrying structures in negative contrast. In nine term (weight 2100-4470 g) and 28 preterm infants (weight 550-2070 g; gestational age 24-33 wk) red blood cell velocity and vessel diameter and density were determined off-line with the Cap-Image program in vessels video-recorded by OPS near the axilla on d 1 and 5 of life. Blood pressure, heart rate, hematocrit, and body and incubator temperature were noted. Vessel diameter ranged from 6 to 24 microm, vessel density from 219 to 340 cm/cm(2) with no change between d 1 or 5 and no difference between term and preterm infants. Red blood cell velocity increased in preterm infants from d 1 [median 528 microm/s, 95% confidence interval (CI) 486-564 microm/s] to d 5 (median 570 microm/s; 95% CI 548-662 microm/s; p = 0.001) and correlated with the decrease in median hematocrit from 44% (CI 40%-60%) to 39% (CI 37%-43%) with r(2) = -0.37 with a 95% CI -0.59 to -0.11, p = 0.006. Hematocrit correlates with red blood cell velocity in the microvessels of the skin. The new technology can be used to assess quantitative changes in the microvessels and thus allows noninvasive assessment of tissue perfusion in term and preterm infants.