MedicalResearch.com Interview with:
Barnaby C. Reeves, D.Phil.
Professor of Health Services Research, Clinical Trials & Evaluation Unit
School of Clinical Sciences, University of Bristol
Bristol Royal Infirmary Bristol
Medical Research: What is the background for this study?
Response: Variable decisions are made about when to transfuse patients after cardiac surgery. The circumstances of particular patients influence decisions about whether to give a transfusion.
Transfusion is a life-saving intervention when a patient is experiencing life-threatening bleeding but most patients have only one or two units of red cells transfused. These transfusions are given at varying levels of anaemia. Some doctors prefer to give a transfusion after cardiac surgery when a patient is only mildly anaemic, believing that the transfusion will promote recovery, while other doctors prefer to wait to transfuse until a patient is substantially anaemic, believing that a transfusion may do more good than harm and is wasteful if it is not needed. Therefore, we carried out a randomized controlled trial comparing restrictive (transfuse when haemoglobin <7.5 g/dL) and liberal transfusion thresholds (transfuse when haemoglobin <9.0 g/dL).*
Medical Research: What are the main findings?
Response: We obtained written informed consent before surgery but only randomized participants after surgery, in intensive care, if their Hb dropped below 9 g/dL. (Hence, we recruited over 3,500 patients but randomized only 2007.) This design avoids ‘diluting’ any difference between groups by including participants who would not usually be ‘considered’ for transfusion.
The primary outcome was the occurrence of one or more serious complications: heart attack, stroke, acute kidney injury, bowel infarction, infection; this included/involved 35.1% of the patients in the restrictive-threshold group and 33.0% of the patients in the liberal-threshold group. This slight difference – more in the restrictive group – was not statistically significant.
We then compared the percentages of patients who died; these were 4.2% in the restrictive group and 2.6% in the liberal group. The difference in this secondary outcome was of borderline statistical significance. Frequencies of other secondary outcomes (infections, ischaemic events, days in critical care and hospital, pulmonary complications) were not different in the two groups.
We also carried out some pre-specified sensitivity analyses for the primary outcome and all-cause mortality. The two most important ones aimed to avoid dilution of the difference between groups as a result of patients having transfusions or outcome events before randomization. Excluding patients who were transfused before randomization shifted the treatment effect to favour the liberal threshold more strongly, for both the primary outcome and mortality. Excluding patients who experienced an outcome event in the first 24 hours after randomization did not change the treatment effect for either outcome. Continue reading