The authors conducted a database review of close to 1.6 million patients undergoing surgery at 346 hospitals in the USA to determine whether red blood cell transfusions on the day of operation or the next day were associated with an increase in stroke or myocardial infarction within 30 days after surgery. Included patients had non-cardiac, non-intracranial and non-vascular surgery. The authors’ assumption was that stored red blood cells undergoes biochemical and morphological changes that could impair post-transfusion oxygen delivery and contribute to ischaemic outcomes.
The authors conclude that “a perioperative transfusion of one unit of packed red blood cells is associated with increased odds of perioperative ischaemic stroke and/or myocardial infarction”. However, when one looks at their results, one sees that the association for transfusion of 1 unit is not, overall, significant; in addition, it was not significant for small bowel resections, hip and knee replacements and spine surgery. The authors also mention that “the fraction of risk attributable to transfusion itself, however, was substantially smaller than for non-modifiable comorbid conditions”.
One should remember that such studies are useful to generate hypotheses for future randomised controlled trials (RCT) but that their conclusions must be acknowledged with caution. The relationship between transfusions and outcomes is difficult to establish outside a RCT because of the so-called “indication bias”, i.e. no statistical method is capable of distinguishing whether the underlying disease or the transfusion caused the adverse outcomes.
Finally, the authors’ underlying assumptions regarding the problems associated with stored blood have been invalidated by the results of the ABLE study (Lacroix J et al. N Engl J Med 2015;372:1410-8).
– Jean-François Hardy