New research has shown that patients having heart surgery do not benefit if doctors wait until a patient has become substantially anaemic before giving a transfusion.
In the UK, about half of all patients having cardiac surgery are given a red blood cell transfusion after the operation, using up to ten per cent of the nation's blood supply. The proportion of patients having a transfusion is high because blood loss and severe anaemia are common after cardiac surgery and transfusion is the preferred treatment. Blood loss causes anaemia which doctors detect by measuring the red cell count or haemoglobin level - a low level triggers transfusion.
The trial, led by academics at the University of Bristol, and published in the New England Journal of Medicine, was carried out to resolve uncertainty about when to give blood transfusions after heart surgery. The trial, funded by the National Institute for Health Research Health Technology Assessment (NIHR HTA) Programme, compared two groups of patients, one which had transfusions at a low haemoglobin level and the other which had transfusions at a higher haemoglobin level.
Cardiac surgery patients who receive blood transfusions are believed to have more complications such as infections, heart attacks and strokes, and this has led to speculation that avoidance of transfusion will improve clinical outcomes.
Unnecessary blood transfusions may also increase healthcare costs both directly, because blood is an increasingly scarce and expensive resource, and indirectly due to the complications associated with transfusion. However, the association between transfusions and complications does not necessarily mean that transfusions are bad for patients because sicker patients are more likely to have a transfusion. Better evidence is needed to guide transfusion decisions.
To resolve this issue doctors and researchers from the universities of Bristol and Oxford conducted a randomised controlled trial to compare policies of transfusing cardiac surgery patients at a 'low' or 'high' haemoglobin level. The aim of the study was to determine whether transfusing at a low level was safer, or more cost-effective, as has been shown in other patient groups.
Patients over 16 years of age undergoing non-emergency cardiac surgery were recruited to the clinical trial at 17 UK hospitals. Participants with a haemoglobin (Hb) level of less than 9 g/dL after their operations were randomised to have a transfusion either when they became substantially anaemic (transfuse when Hb is 'low,' i.e. less than 7.5 g/dL) or straightaway, when they were mildly anaemic (transfuse when Hb is 'high,' i.e. less than 9 g/dL).
To compare the two transfusion strategies the research team counted the number of patients who had a serious infection, stroke, heart attack, dead gut or kidney failure during the first three months after the operation. The trial analysed information for 2,003 participants, about four times more than the next largest similar trial of low and high thresholds for transfusion in patients having heart surgery.
