Blood transfusion increases functional capillary density in the skin of anemic preterm infants.

Direct visualization of the microcirculation at the level of the skin capillaries may provide information on the quality of tissue perfusion. Orthogonal polarization spectral imaging (OPS) enables noninvasively direct observation of those blood vessels. OPS was applied to the upper arm of 13 preterm anemic infants [median (95% confidence interval) gestational age: 26 wk (25-26 wk); birth weight: 730 g (652-789 g)] before and 2 and 24 h after transfusion (Tx). OPS images of skin perfusion were continuously recorded on video. Off-line quantitative data of microvascular perfusion were obtained by measuring functional capillary density, vessel diameter, red blood cell velocity, and flow. We found a significant increase in functional capillary density 2 h after transfusion with an additional significant rise after 24 h [before: 142 (134-155); 2 h after Tx: 185 (166-196); 24 h after Tx: 206 (185-219) cm/cm2; p < 0.001), thus indicating improved microvascular perfusion. Vessel diameter, red blood cell velocity, and flow did not change significantly. There were no significant changes in clinical variables, such as blood pressure, heart rate, or body temperature. Whereas conventional monitoring methods did not show any changes after transfusion, quantitative analyses of OPS images indicated improved perfusion; hence, it seems a useful monitor for assessing the response to therapies aimed to improve tissue perfusion.