Microcirculatory effects of red blood cells with different hemoglobin oxygen affinity in hemorrhagic shock

Abstract

Autoregulation can be considered to be a balance between blood flow and O2 extraction. Local regulatory mechanisms prevent excessive local O2 supply to tissue upstream arteriolar vasoconstriction. Effects of resuscitation with red blood cells (RBCs) with low and high P50 (partial pressure of O2 at 50% Hb saturation) were studied with the hamster window chamber in a model of 1 h shock. Introduction of inositol hexaphosphate (IHP) and 5‐hydroxymethyl‐2‐furfural (5HMF) into the RBCs by electroporation decreased and increased the P50 to 10 and 50 mmHg respectively (normal p50 = 32 mmHg). The animals were resuscitated with 25% of blood volume infusion using either the low and high P50 RBCs. Systemic parameters, microvascular hemodynamics, and functional capillary density (FCD, the number of capillaries perfused per unit area), were measured up to 90 min after resuscitation. RBCs with high P50 (reduced Hb‐O2 affinity) reduced arteriolar diameter and flow, and increased the oxygen extraction. RBCs with low P50 (increased Hb‐O2 affinity) had higher levels of systemic O2 delivery and tissue pO2. In summary, resuscitation with RBCs with increased Hb‐O2 affinity maintained adequate microhemodynamic conditions and tissue PO2 while RBCs with reduced Hb‐O2 affinity produced arteriolar vasoconstriction followed by higher O2 extraction and lower tissue PO2.Supported in part by Bolsista CNPq, HL076182 and HL076182.