Optimal hematocrit in an artificial microvascular network

Abstract

BACKGROUND Higher hematocrit increases oxygen carrying capacity of blood, but also increases blood viscosity, thus decreasing blood flow through the microvasculature and reducing the oxygen delivery to tissues. Therefore, an optimal value of hematocrit that maximizes tissue oxygenation must exist. STUDY DESIGN AND METHODS We used viscometry and an artificial microvascular network (AMVN) device to determine optimal hematocrit in vitro. Suspensions of fresh red blood cells (RBCs) in plasma, normal saline or a protein-containing buffer, and suspensions of stored RBCs (at week 6 of standard hypothermic storage) in plasma with hematocrits ranging 10 – 80% were evaluated. RESULTS For viscometry, optimal hematocrits were 10, 25.2, 31.9, 37.1 and 37.5% for fresh RBCs in plasma at shear rates of ≤3.2, 11.0, 27.7, 69.5, and 128.5 s−1. For the AMVN, optimal hematocrits were 51.1, 55.6, 59.2, 60.9, 62.3 and 64.6% for fresh RBCs in plasma and 46.4, 48.1, 54.8, 61.4, 65.7 and 66.5% for stored RBCs in plasma at pressures of 2.5, 5, 10, 20, 40 and 60 cmH2O. CONCLUSION Although exact values of optimal hematocrit may depend on specific microvascular architecture, our results suggest that optimal hematocrit for oxygen delivery in the microvasculature depends on perfusion pressure. Anemia in chronic disorders may, therefore, represent a beneficial physiological response to reduced perfusion pressure resulting from decreased heart function and/or vascular stenosis. Our results may help explain why therapeutically increasing hematocrit in such conditions with RBC transfusion frequently leads to worse clinical outcomes.

Development of a flow standard to enable highly reproducible measurements of deformability of stored red blood cells in a microfluidic device

“…Our results suggest that changes unfold in two phases bridged by a 2‐week plateau (between Days 7 and 21) when changes in RBC deformability are not statistically significant. Previous reports of deformability impairment occurring before Day 7 or after Day 21 are partly in line with our observations . Bennett‐Guerrero et al concluded that RBC deformability measured using ektacytometry was gradually altered over the 42‐day storage period.…”

“…Preliminary assays (Fig. S1, available as supporting information in the online version of this paper) has shown that the flow rate of RCC sample was inversely influenced by its Hct level, which is in line with observations in similar microfluidic systems . The RBCs settling behavior of slow initial sedimentation phase followed by fast sedimentation phase was depicted by an initial steady flow rate followed by a flow rate decreases.…”

Influence of feeding hematocrit and perfusion pressure on hematocrit reduction (Fåhræus effect) in an artificial microvascular network

“…41 We have previously calculated theoretical oxygen transport effectiveness to assess optimal Hct values viscometrically and with the AMVN device. 42 In the present study, estimated oxygen transport effectiveness was highest at a Hct feeding of approximately 60% in all capillary microchannels studied ( Figure 6). The oxygen transport effectiveness decreased by approximately 50% in all microchannels when the differential ΔP was reduced from 60 to 5 cm H 2 O (Figure 7).…”

Rational red blood cells administration - have we achieved a satisfactory level?

“…RBC transfusion in patients with anemia in whom compensatory mechanisms for adequate tissue oxygenation are reduced increases the capacity for oxygen transport [18]. A well-compensated anemia resulting from iron deficiency is the most common form of anemia and is not an indication for RBC administration itself, but as such requires the administration of iron via oral or intravenous route, with or without erythropoietin and with an assessment of the risk of adverse reactions [19].…”