Concerns Regarding “Acute Normovolemic Hemodilution Significantly Reduces RBC Transfusion and Lactic Acidosis Following Cardiac Surgery—A Propensity-Matched Study”

Dear Editor, We read with interest the current study by Sebt et al.[1] on acute normovolemic hemodilution (ANH) following cardiac surgery, which suggests that ANH dramatically lowers postoperative lactic acidosis and red blood cell (RBC) transfusions. The subject is pertinent and significant regarding patient blood management; yet, certain methodological and interpretation issues warrant additional examination. First, the study relies on a retrospective, single-center design, and although propensity score matching was performed, residual confounding cannot be excluded. Significantly, intraoperative hemodynamic parameters—such as central venous pressure, cardiac output, or mixed venous oxygen saturation (SvO₂)—are not documented. The intrinsic reduction of oxygen-carrying capacity due to hemodilution greatly constrains mechanistic interpretation in the absence of perfusion data during cardiopulmonary bypass (CPB). Was the noted decrease in lactic acidosis genuinely attributable to ANH, or might alternative factors (e.g., reduced CPB durations, enhanced perfusion techniques) have played a role? Second, the authors employed lactate levels exceeding 2 mmol/L as a binary indicator of lactic acidosis. However, this threshold is not specific in the context of perioperative cardiac surgery, where transient lactate elevations are frequent and not necessarily pathogenic. A more meaningful evaluation of metabolic derangement may be provided by time-weighted lactate exposure or lactate clearance. Third, the baseline hematocrit values and the degree of hemodilution achieved are not explicitly delineated. It is widely recognized that the efficacy of ANH is significantly influenced by the patient’s volume status and preoperative hemoglobin levels. The generalizability of the findings is restricted in the absence of subgroup analysis stratified by baseline hematocrit or type of surgery (e.g., isolated CABG vs. complex valve procedures). Furthermore, the exclusion of patients with renal dysfunction or those undergoing emergency surgery may have introduced selection bias. It is arguable that these populations are the most susceptible to hemodilution-related effects or may benefit the most. In order to more accurately characterize the boundaries of safe ANH implementation, future research should endeavor to incorporate these high-risk groups. In conclusion, while Sebt et al.’s[1] study contributes to the growing interest in ANH, the evidence presented does not definitively indicate a causal link between ANH and improved metabolic outcomes. Before recommending widespread implementation of ANH as normal practice in cardiac surgery, prospective, randomized trials with complete intraoperative monitoring and stratified analysis must be conducted. Sincerely, Melike Korkmaz Toker Bugra Harmandar Financial support and sponsorship The authors received no financial support for the research, authorship, and/or publication of this article. Conflict of interest There are no conflicts of interest.