Less is More: Study reveals Benefits of Acute Normovolemic Hemodilution in Heart Surgical Outcomes

Recently published study focuses on the implications of acute normovolemic hemodilution (ANH) on red blood cell (RBC) transfusion rates and the occurrence of short-term complications in patients undergoing cardiac surgery. Recognizing that bleeding is a critical complication during heart surgeries, which often leads to the necessity of allogeneic blood transfusions, the investigation highlights the need for alternative strategies like ANH to potentially mitigate adverse transfusion-related outcomes.

Methodology

An extensive quasi-experimental design was employed, encompassing 2,271 patients at a referral hospital, with a rigorous propensity-score matching approach applied to balance the cohort effectively. This matching resulted in 778 patients divided into two groups: those receiving ANH (389 patients) and those not receiving it (389 patients). The matching was successful as there were no significant differences in demographic, clinical, and procedural variables between the two groups.

Results

The results revealed that ANH led to a statistically significant reduction in both the rate and volume of RBC transfusions. Specifically, the RBC transfusion rate dropped from 60.9% to 50.9% in the ANH group (risk ratio: 0.84; P = 0.006) and the number of transfused RBC units was decreased by an average of 0.24 units. However, the study did not identify any differences in the transfusion of fresh frozen plasma (FFP) and platelets between groups.

Complications

In terms of complications, the incidence of lactic acidosis—a condition defined as elevated serum lactate levels—was notably reduced by 53%, from 11.3% in the non-ANH group to 6.8% in the ANH group (risk ratio: 0.47; P < 0.001). This observation suggests that ANH could enhance tissue perfusion and reduce blood viscosity, possibly leading to improved coronary blood flow and efficiency in oxygen delivery.

Postoperative Outcomes

Conversely, the study found no significant differences in various short-term postoperative outcomes, including mortality, incidences of re-intubation, re-exploration due to bleeding, delayed sternal closure, length of ICU stays, or duration of mechanical ventilation. Despite the apparent benefits regarding RBC transfusions and lactic acidosis, the lack of other adverse effects underscores the potential safety of ANH as a blood conservation method in cardiac surgeries.

Limitations

The authors pointed out several limitations to their findings. Even with rigorous propensity score matching, there may still be residual confounding factors that were not accounted for, including variations in individual patient characteristics and other technical aspects of the surgeries performed. Additionally, the study did not assess certain postoperative outcomes, such as infections or acute kidney injury. In conclusion, the findings of this large, rigorously matched study substantiate that mild-volume ANH could significantly decrease both the rate and volume of RBC transfusions along with the incidence of lactic acidosis in cardiac surgery patients, while not adversely affecting other short-term outcomes. These implications suggest that ANH can be an effective blood conservation technique. Nonetheless, further randomized clinical trials are recommended to validate these results and explore the broader implications of ANH in diverse patient populations.

Key Points

- The study investigates the impact of acute normovolemic hemodilution (ANH) on red blood cell (RBC) transfusion rates and short-term complications in patients undergoing cardiac surgery, aiming to address the complications arising from bleeding and the need for allogeneic blood transfusions.

- A quasi-experimental design involving 2,271 patients at a referral hospital was utilized, with propensity-score matching resulting in 778 patients evenly divided into two groups: those receiving ANH and those not receiving it, effectively balancing demographic, clinical, and procedural variables.

- ANH significantly reduced the RBC transfusion rate (from 60.9% to 50.9%; risk ratio: 0.84; P = 0.006) and the average number of transfused RBC units by 0.24 units, although no significant differences were observed in the use of fresh frozen plasma (FFP) and platelets between the two groups.

- The incidence of lactic acidosis decreased by 53% in the ANH group (from 11.3% to 6.8%; risk ratio: 0.47; P < 0.001), indicating possible improvements in tissue perfusion and oxygen delivery efficiency due to ANH.

- No significant differences in short-term postoperative outcomes were reported, such as mortality, re-intubation, re-exploration for bleeding, delayed sternal closure, ICU stay duration, or mechanical ventilation time, suggesting the potential safety of ANH in cardiac surgeries.

- Limitations acknowledged include potential residual confounding factors not accounted for despite matching, as well as the lack of assessment for specific postoperative complications like infections or acute kidney injury, highlighting the need for further randomized clinical trials to validate the findings and assess broader applications of ANH.

Reference –

Vala Sebt et al. (2025). Acute Normovolemic Hemodilution Significantly Reduces RBC Transfusion And Lactic Acidosis Following Cardiac Surgery-A Propensity-Matched Study.. *Annals Of Cardiac Anaesthesia*, 28 2, 136-142. https://doi.org/10.4103/aca.aca_192_24.