<qa>  What is the gold standard of hemoglobin measurement?Non-invasive measurement of hemoglobin in infants and neonates scheduled for elective congenital heart surgery, weighing between 3kg and 20 kg. SpHb measurement will be compared to the gold standard of hemoglobin measurement - CO-oximetrie - and to the point-of-care GEM 3500 premiere. Data collection whenever an arterial blood gas analysis is indicated by the experienced attending anesthetist - before and after cardiopulmonary bypass. 