Electron paramagnetic resonance oximetry as a novel approach to monitor the effectiveness and quality of red blood cell transfusions

Abstract

Background. The goal of red blood cell transfusion is to improve tissue oxygenation. Assessment of red blood cell quality and individualised therapeutic needs can be optimised using direct oxygen (O₂) measurements to guide treatment. Electron paramagnetic resonance oximetry is capable of accurate, repeatable and minimally invasive measurements of tissue pO₂. Here we present preclinical proof-of-concept of the utility of electron paramagnetic resonance oximetry in an experimental setting of acute blood loss, transfusion, and post-transfusion monitoring.      
Materials and methods. Donor rat blood was collected, leucocyte-reduced, and stored at 4 °C in AS-3 for 1, 7 and 14 days. Red blood cell morphology, O₂ equilibrium, p50 and Hill numbers from O₂ binding and dissociation curves were evaluated in vitro. Recipient rats were bled and maintained at a mean arterial pressure of 30-40 mmHg and hind limb muscle (biceps femoris) pO₂ at 25-50% of baseline. Muscle pO₂ was monitored continuously over the course of experiments to assess the effectiveness of red blood cell preparations at different stages of blood loss and restoration. 
Results. Red blood cell morphology, O₂ equilibrium and p50 values of intra-erythrocyte haemoglobin were significantly altered by refrigerated storage for both 7 and 14 days. Transfusion of red blood cells stored for 7 or 14 days demonstrated an equivalently impaired ability to restore hind limb muscle pO₂, consistent with in vitro observations and transfusion with albumin. Red blood cells refrigerated for 1 day demonstrated normal morphology, in vitro oxygenation and in vivo restoration of tissue pO₂. 
Discussion. Electron paramagnetic resonance oximetry represents a useful approach to assessing the quality of red blood cells and subsequent transfusion effectiveness.