In response: Not all acute normovolemic hemodilutions are created equal
Abstract
We read with great interest the work by Li et al. The authors hypothesized that red blood cell (RBC) transfusions in orthognathic surgery could be reduced by acute normovolemic hemodilution (ANH); 187 patients were randomly assigned to conventional management or ANH. There is a renewed interest in ANH as part of perioperative multimodal blood conservation strategy. Their study is a welcome addition to the ANH literature; however, further discussion and comment are warranted for the study design and indication of ANH. First, the authors calculated the sample size based on their historical RBC transfusion rate (13.8%); ANH was presumed pre-hoc to drop the rate from 14% to 2%. However, the overall rate of transfusion was 2.04% (4 of 196) in the intention-to-treat analysis; 3.0% in the control and 1.05% in ANH group. To detect a transfusion rate change from 3.0% to 1.05% using ɑ of .05 and β of .2, we estimate the required total sample size to be 1820. Interestingly, the authors reported a higher rate of RBC transfusion (26.7%) among 30 patients who refused to participate in the study. There seems to be a gap in allogeneic transfusion rates between the enrolled patients and non-study patients. A possible explanation is the Hawthorne effect; providers' knowledge about the blood conservation trial might have led to more restrictive transfusion practice in the studied population. The authors also referred to a 13% transfusion rate in the study published in 1996; however, due to…
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