Blood Transfusion Increases Functional Capillary Density in the Skin of Anemic Preterm Infants

Abstract

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 ; 24 h after Tx: 206 (185-219) cm/cm 2 ; p Ͻ 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. Transfusion practices for neonates are controversial, variable, and based on limited scientific information. This inconsistent approach stems from incomplete knowledge of the effects of anemia in infants and a lack of controlled studies. This results in no clearly established indications for transfusions (Txs) in neonates. The decision to transfuse is frequently based on clinical signs, such as episodes of apnea and bradycardia or failure to gain weight. Data on the effects of blood Tx on these clinical parameters, however, are conflicting (1,2). Peripheral fractional oxygen extraction may be a better indicator for the need of Tx. This concept, however, did not seem applicable in the clinical setting, because in a pilot study of anemic infants, indication for Tx was not influenced by the fractional oxygen extraction value (3).The effect of hemodilution on capillary perfusion has been investigated extensively in the hamster skinfold model using intravital microscopy (4 -7). Orthogonal polarization spectral imaging (OPS) has been developed as a noninvasive technique to investigate the human microvasculature and can be used even in small infants (8). The technology has been described in detail elsewhere (9). In brief, through the use of special optics, a virtual light source is created within the tissue and the light is absorbed by Hb, yielding an image of the illuminated Hb-carrying structures in negative contrast. We have previously shown that microvessel diameter, red blood cell velocity (RBC vel), and functional vessel density can be measured noninvasively by OPS in the skin of term and preterm infants (8). The aim of the...

Orthogonal polarization spectroscopy to detect mesenteric hypoperfusion

“…OPS data for functional vessel density, diameter of microvessels, and red blood cell velocity correlated well with data obtained by fluorescence microscopy [7,13]. Despite the use of OPS imaging in a variety of conditions and organs [8,11,12,16,24], and the attractiveness of direct visualization of microcirculation, the quantification of changes and their physiologic and clinical relevance remains controversial [1, 4, 8, 11, 12, 15-18, 23, 24]. The proposed criteria include visible capillaries, clearly visible flow of individual erythrocytes versus large thrombosed vessels coursing in a criss-cross fashion [11,12], vessel diameter, red blood cell velocity [10,19,20], and functional capillary density [8,15,16,24].…”

Functional Vessel Density in the First Month of Life in Preterm Neonates

“…Diameters of the vessels measured in our study ranged from 7 to 24 m. In neonates, vessels larger than 25 to 30 m are deeper in the dermis and only small loops can be observed before the vessel disappears into the deeper layer (33,34). In neonates due to the small size of the vessel, arterioles, capillaries, and post capillary venules cannot be clearly distinguished (8,9).…”

“…The recent development of new technologies has helped to investigate these changes in adult patients with sepsis (5)(6)(7). Previous studies have shown that parameters of microcirculation such as microvessel diameter, red blood cell velocity, and functional small vessel density (FSVD) can be measured in the skin of term and preterm infants by Orthogonal Polarization Spectral (OPS) imaging in the first week of life (8) and that FSVD increases after elective blood transfusion in anemic neonates (9). The microcirculation of the skin plays an important role in maintaining a constant body temperature and in regulating the fluid balance (10,11).…”

Microcirculatory mechanisms in postnatal hypotension affecting premature infants

“…SDF images of 10 s were obtained on three different spots of the right inner upper arm (preductal arm). As we have shown previously, the upper region of the arm provides a good image quality and is easy to access (36)(37)(38).…”