The lactate risk score (LRS): Anticipating hyperlactatemia during cardiopulmonary bypass

Abstract

Hyperlactatemia during cardiopulmonary bypass (CPB) is a marker of inadequate oxygen delivery and correlates with postoperative morbidity and mortality. Although lactate is measured directly via enzymatic sensors, its rise can be anticipated through perfusion, hemodynamic, and metabolic indicators. We reviewed the literature and synthesized a Lactate Risk Score (LRS) weighted by published population data, focusing on adult cardiac surgery procedures performed under mild hypothermia (34–36°C). A Evidence-based Conceptual Review (PubMed, Embase, Scopus, up to September 2025) was conducted using keywords lactate, oxygen delivery, DO₂, carbon dioxide production, vasoactive drugs, arterial pressure, glucose, microemboli, cardiopulmonary bypass duration, cardiac surgery. Studies reporting perfusion thresholds linked with lactate levels in adult cardiac surgery were prioritized. Weighting of score components reflected both the strength of association and the population size of published cohorts. Across the literature, indexed oxygen delivery (DO₂i) below 260–280 mL/min/m² emerged as the strongest predictor of lactate increase and was assigned +2 points in the score. Similarly, indexed carbon dioxide production greater than 60 mL/min/m² (+2) and a DO₂i/VCO₂i ratio lower than 5 (+2) were strongly correlated with anaerobic metabolism. An oxygen extraction ratio ≥ 0.35 (+1) and a venous-to-arterial CO₂ gap ≥ 6 mmHg or a Pv–PaCO₂/Ca–CvO₂ ratio ≥ 1.8 (+1) added further risk information. The cumulative oxygen debt, quantified as the area under the curve of DO₂ below the critical threshold, was weighted with +2 points, while prolonged CPB duration increased the score according to time: >90 min (+1), >120 min (+2), and >180 min (+3). Hemodynamic instability with mean arterial pressure or arterial line pressure persistently <50 mmHg was considered highly relevant and attributed +2 points, and the requirement for noradrenaline infusion >0.05 µg/kg/min was weighted with +1. Among preoperative factors, advanced age, coronary artery disease, and baseline hemoglobin <8 g/dL were each scored +1. Metabolic stress, reflected by intraoperative glucose increase >180 mg/dL, added +1, and significant gaseous microembolic activity in the arterial line, defined as more than 500 bubbles per hour or emboli >40 µm diameter, contributed +1. Based on this integration, the Lactate Risk Score ranges from 0 to 18 points, with risk stratification defined as low (0–3), intermediate (4–7), and high (≥8) for the development of clinically significant hyperlactatemia (≥4 mmol/L). The Lactate Risk Score integrates preoperative vulnerability (age, coronary artery disease, anemia), perfusion adequacy, cumulative oxygen debt, CPB duration, hemodynamic stability, vasoactive use, metabolic stress, and gaseous microembolic load. Derived from published cardiac surgery cohorts at 34–36°C, the score provides a structured, evidence-weighted framework to anticipate lactate elevation during CPB. Prospective validation is warranted before clinical adoption.