How to manage the anaemic patient

The reduced haemoglobin (Hb) concentration which characterizes anaemia causes a reduction in arterial oxygen content. However, a rise in cardiac output, due largely to the fall in blood viscosity, and, in chronic anaemia, a shift of the oxygen dissociation curve to the right maintain oxygen delivery to the tissues until very low Hb concentrations are reached. Anaemia is well tolerated in animals and in healthy humans at rest but probably not in patients with cardiac disease. Although the ideal way to manage anaemia is to investigate its cause and to start specific treatment, such a course is often impossible in the anaemic surgical patient, whose anaemia is usually caused by the condition for which the operation is required. The anaesthetist has thus to choose between accepting the patientʹs low Hb level or raising it by transfusion. The evidence available to help in making this decision is discussed. It is impossible to prescribe a single level at which transfusion is always indicated, so it is not surprising that clinical practices differ. The main alternative to transfusion is to keep surgical blood loss to a minimum; methods of achieving this end are considered.