The impact of intraoperative fluid therapy on the risk of hyperlactatemia in patients undergoing cardiac surgery with cardiopulmonary bypass: a prospective single-center study

The objective was to evaluate the association between the volume of intraoperative fluid therapy and the risk of postoperative hyperlactatemia in patients undergoing cardiac surgery with cardiopulmonary bypass.

Materials and methods. This single-center prospective cohort study included 733 adult patients who underwent cardiac surgery with cardiopulmonary bypass between 2024 and 2025. The total intraoperative fluid volume (crystalloids and colloids), normalized to body weight (mL/kg), was used as the exposure variable; the priming volume of the cardiopulmonary bypass circuit was excluded from the analysis. Patients were stratified according to quartiles of fluid volume distribution: the first quartile (Q1) represented the low-volume («restrictive») group, the second and third quartiles (Q2–Q3) represented the moderate-volume group, and the fourth quartile (Q4) represented the high-volume («liberal») group. The quartile boundaries were calculated based on the distribution of infusion volume in the entire study cohort. Hyperlactatemia was defined as a lactate level ≥3 mmol/L within the first 6 hours after admission to the intensive care unit. The type of hyperlactatemia (ischemic or metabolic) was determined using a predefined algorithm incorporating lactate level, ScvO₂, Pv-aCO₂, and lactate clearance at 6 hours. Indicators of tissue hypoperfusion included ScvO₂ < 65%, Pv–aCO₂ > 6 mmHg, and lactate clearance < 10%. Multinomial logistic regression was used to evaluate the independent association between fluid volume and hyperlactatemia type (no hyperlactatemia, ischemic type, metabolic type).

Results. The overall incidence of postoperative hyperlactatemia (lactate ≥3.0 mmol/L within 6 hours after ICU admission) in the general cohort occurred in 30.2% of patients (n = 733). The median intraoperative fluid volume differed significantly between groups (p < 0.001). The incidence of ischemic hyperlactatemia demonstrated a U-shaped relationship with fluid volume: the lowest rate was observed in the moderate-volume group (9.5% per the entire group of patients), whereas in the low-volume («restrictive») group, the frequency increased (13.1%), and the probability of this type of hyperlactatemia also increased according to regression analysis (OR 1.52; 95% CI 1.01–2.29; p = 0.04), peaking in the high-volume («liberal») group (18.0%; OR 1.95; 95% CI 1.28–2.98; p = 0.002). When fluid volume was analyzed as a continuous variable, the lowest predicted risk of ischemic hyperlactatemia corresponded to an infusion range of approximately 35–45 mL/kg. The incidence of metabolic hyperlactatemia differed between groups (p = 0,001), but without a consistent pattern and without a nonlinear association.

Conclusion. In patients undergoing cardiac surgery with cardiopulmonary bypass, a U-shaped association was observed between the volume of intraoperative fluid therapy and the risk of ischemic hyperlactatemia following cardiac surgery with cardiopulmonary bypass. The lowest risk of hypoperfusion-related hyperlactatemia was observed with a moderate fluid volume of approximately 35–45 mL/kg. These findings suggest that a moderate intraoperative fluid strategy may be associated with a more favorable postoperative tissue perfusion profile in cardiac surgical patients.

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