Loss or Dilution-A New Diagnostic Method to Assess the Impact of Dilution on Standard Laboratory Parameters

Nicole Innerhofer; Sasa Rajsic; Marco Ronzani; Robert Breitkopf; Can Gollmann Tepeköylü; Corinna Velik-Salchner; Lisa Schlosser; Dietmar Fries; Werner Streif; Michael Schirmer; Judith Martini

doi:10.3390/diagnostics13152596

Loss or Dilution-A New Diagnostic Method to Assess the Impact of Dilution on Standard Laboratory Parameters

Diagnostics (Basel). 2023 Aug 4;13(15):2596. doi: 10.3390/diagnostics13152596.

Affiliations

¹ Department of Anesthesiology and Intensive Care Medicine, Medical University Innsbruck, 6020 Innsbruck, Austria.
² Department for Cardiac Surgery, Medical University of Innsbruck, 6020 Innsbruck, Austria.
³ Department of Mathematics, University of Innsbruck, 6020 Innsbruck, Austria.
⁴ Department of Paediatrics, Medical University of Innsbruck, 6020 Innsbruck, Austria.
⁵ Department of Internal Medicine, Medical University of Innsbruck, 6020 Innsbruck, Austria.

Abstract

Intraoperative fluid therapy is regularly used in patients undergoing cardiac surgery procedures with cardiopulmonary bypass (CPB). Although fluid administration has several advantages, it unavoidably leads to hemodilution. The hemodilution may further influence the interpretation of concentration-based laboratory parameters like hemoglobin (Hgb), platelet count (PLT) or prothrombin time (PT). These all parameters are commonly used to guide blood product substitution. To assess the impact of dilution on these values, we performed a prospective observational study in 174 patients undergoing elective cardiac surgery. We calculated the total blood volume according to Nadler's formula, and fluid therapy was correlated with a newly developed dilution coefficient formula at the end of CPB. Intravenously applied fluids were measured from the beginning of the anesthesia (baseline, T₀) and 15 min after the end of protamine infusion (end of CPB, T₁). The amount of the administered volume (crystalloids or colloids) was calculated according to the percentage of the intravascular fluid effect, and intraoperative diuresis was further subtracted. The median blood volume increased by 148% in all patients at T₁ compared to the calculated total blood volume at T₀. This led to a dilution-dependent decrease of 38% in all three parameters (Hgb 24%, corrCoeff = 0.53; PLT 41%, corrCoeff = 0.68; PT 44%, corrCoeff = 0.54). The dilution-correlated decrease was significant for all parameters (p < 0.001), and the effect was independent from the duration of CPB. We conclude that the presented calculation-based approach could provide important information regarding actual laboratory parameters and may help in the guidance of the blood product substitution and potential transfusion thresholds. Further research on the impact of dilution and related decision-making for blood product substitution, including its impact on morbidity and mortality, is warranted.

Keywords: biomarkers; blood product substitution; cardiac surgery; dilution; fluid therapy; hemoglobin; platelets; volume therapy.

Grants and funding

This research received no external funding.