Central/mixed venous oxygen saturation and lactate levels might be of limited use as physiologic transfusion triggers in cardiac surgery

Current guidelines differ in their recommendations regarding the use of physiologic transfusion triggers to guide transfusion practice. Data on the interaction between haemoglobin (Hb) and physiologic transfusion triggers, or their response to packed red blood cell (pRBC) transfusions are limited. This study aimed to evaluate the interactions between Hb, mixed/central venous oxygen saturation (SvO2) and lactate levels as well as their changes (ΔSvO2, Δlactate) in response to pRBC transfusion in cardiac surgery patients. Retrospective exploratory data analysis. A 22-bed intensive care unit (ICU) at a single tertiary academic centre and university hospital in Austria. Adult (age ≥ 18 years) patients who underwent cardiac surgery. Pearson correlation coefficients (r) and coefficients of determination (r2) between Hb, mixed/central venous oxygen saturation (SvO2), and lactate levels. Pearson correlation coefficients (r) and coefficients of determination (r2) between ΔSvO2, Δlactate and pretransfusion Hb. A total of 5025 cardiac surgery patients, in whom 20 542 blood gas analyses were performed, were included in the final analysis. Correlations between Hb levels and SvO2 (r2 = 0.026, P < 0.001) and between Hb and lactate levels (r2 = 0.001, P < 0.001) were statistically significant but weak overall. No correlations were found between ΔSvO2 (r2 = 0.002, P = 0.13) or Δlactate (r2 = 0.003, P = 0.087) and pretransfusion Hb levels. Hb, SvO2 and lactate levels were only weakly correlated with each other, and changes in SvO2 and lactate levels in response to pRBC transfusion did not correlate with pretransfusion Hb. Our findings question the usefulness of SvO2 and lactate levels as physiologic transfusion triggers to guide transfusion practice in cardiac surgery patients. Johannes Kepler University Ethics Committee Study Reference Number 1063/2023.