Abstract: We identified 11 trials (862 participants). All trials were in neonatal or paediatric populations. The trials covered only three areas of interest: restrictive versus liberal transfusion triggers (two trials), leukoreduction versus non-leukoreduction (two trials) and standard versus non-standard cardiopulmonary bypass (CPB) prime (seven trials). Owing to the clinical diversity in the participant groups (cyanotic (three trials), acyanotic (four trials) or mixed (four trials)) and the intervention groups, it was not appropriate to pool data in a meta-analysis. No study reported data for all the outcomes of interest to this review. Risk of bias was mixed across the included trials, with only attrition bias being low across all trials. Blinding of study personnel and participants was not always possible, depending on the intervention being used. Five trials (628 participants) reported the primary outcome: 30-day mortality. In three trials (a trial evaluating restrictive and liberal transfusion (125 participants), a trial of cell salvage during CPB (309 participants) and a trial of washed red blood cells during CPB (128 participants)), there was no clear difference in mortality at 30 days between the intervention arms. In two trials comparing standard and non-standard CPB prime, there were no deaths in either randomised group. Long-term mortality was similar between randomised groups in one trial each comparing restrictive and liberal transfusion or standard and non-standard CPB prime. Four trials explored a range of adverse effects following red cell transfusion. Kidney failure was the only adverse event that was significantly different: patients receiving cell salvaged red blood cells during CPB were less likely to have renal failure than patients not exposed to cell salvage (risk ratio (RR) 0.26, 95% confidence interval (CI) 0.09 to 0.79, 1 study, 309 participants). There was insufficient evidence to determine whether there was a difference between transfusion strategies for any other severe adverse events. The duration of mechanical ventilation was measured in seven trials (768 participants). Overall, there was no consistent difference in the duration of mechanical ventilation between the intervention and control arms. The duration of intensive care unit (ICU) stay was measured in six trials (459 participants). There was no clear difference in the duration of ICU stay between the intervention arms in the transfusion trigger and leukoreduction trials. In the standard versus non-standard CPB prime trials, one trial examining the impact of washing transfused bypass prime red blood cells showed no clear difference in duration of ICU stay between the intervention arms, while the trial assessing ultrafiltration of the priming blood showed a shorter duration of ICU stay in the ultrafiltration group. There are only a small number of small and heterogeneous trials so there is insufficient evidence to assess the impact of red cell transfusion on patients with congenital heart disease undergoing cardiac surgery accurately. It is possible that the presence or absence of cyanosis impacts on trial outcomes, which would necessitate different clinical management of two groups. Further adequately powered, specific, high-quality trials are warranted to assess this fully.

Plain-language summary: We searched scientific sources to identify eligible trials and found 11 studies with 862 participants. We found no trials including adults. The identified studies examined three treatments: two trials compared giving a red blood cell transfusion only when the levels of haemoglobin in the blood fell below a certain concentration (known as a restrictive versus a liberal transfusion trigger); two trials compared whether there was a benefit to removing white blood cells (leukocytes) from the transfused red blood cells and seven trials compared methods used to prepare the fluid for the CPB machine. The trials were different in terms of the age of the participants, the type of heart disease and the exact treatment studied so there was been no opportunity to pool data for analysis. All studies did not report on all outcomes (a measure of a participant's clinical and functional status that is used to assess the effectiveness of a treatment, e.g. death, side effects). Key results Our primary outcome was death within 30 days after surgery. Five trials looked at this outcome and found no clear difference in mortality between the treatment arms. Four trials explored other adverse effects following a red blood cell transfusion. A difference in the number of adverse events was only observed for kidney failure: in one trial (with 309 participants), patients receiving cell salvaged red blood cells during CPB were less likely to have renal failure than patients not exposed to cell salvage. Quality of the evidence This review identified only a few, small studies across three interventions. These studies measured many different aspects of red blood cell transfusion in patients having heart surgery so it is difficult to make accurate conclusions about the benefits or risks of red blood cell transfusion for these patients. More research is needed to allow accurate conclusions. Future studies should be bigger and focus on one aspect of transfusion in a specific type of heart disease.