370 ANAEMIA/HYPOVOLAEMIA: AN UNSUPECTED CAUSE OF IMPAIRED OXYGEN (02)' TRANSPORT AFTER CARDIAC SURGERY

Abstract

Adequate blood volume (BV) is important for organ perfusion; haemodynamic monitoring and clinical assessment may be misleading. In a study of children, < 48hrs after cardiac surgery, we compared measured BV and red cell volume (RCV) with [Hb] and Hct with a scoring system (SS) for hypovolaemia, in children who were clinically stable. RCV was measured using biotin-labelled autologous red cells.Twelve measurements were made in 10 children at from 2-11 days after surgery; mediam (range): age 28 days (2-3,549);weight 3.3kg(1-25.6). All required respiratory support (Sa O2 65-98%). RCV ranged from 14-33 ml/kg, BV 42-94 ml/kg. Significant depletion of BV and RCV was found in all, compared with normal, physiological predicted requirements. Neither Hct nor SS predicted RCV (r2=36%, 25%, 1%) or BV (r2=2%,0.1%,2%).Suboptimal BV is common and may cause impaired O2 transport after cardiac surgery. Standard assessment techniques are unreliable but biotin labellei red cells can be used to quantitate RCV and BV. Normalization of BV and RCV after bypass surgery may lead to reduction in pest operative morbidity.