We read with great interest the article by Kowara et al.,^[1] which highlights the potential of PvCO2 × Ve/Q as a key predictive marker for hyperlactatemia during cardiopulmonary bypass (CPB). This study is an important step toward identifying reliable, real-time markers for monitoring hypoperfusion. However, several critical aspects of this work deserve further discussion.

The authors show that PvCO2 × Ve/Q predicts lactate kinetics with high sensitivity, though its specificity (55.6%) is modest. This raises the risk of false-positive alerts, leading to unnecessary interventions during CPB. To improve accuracy, combining PvCO2 × Ve/Q with other parameters like oxygen extraction ratio or respiratory quotient could enhance its clinical value.^[2,3] Continuous monitoring of PvCO2 × Ve/Q instead of intermittent sampling could provide dynamic assessments and support real-time decisions.

The study’s exclusion criteria such as preoperative lactate levels >2 mmol/L and pump flow indices outside 1.2–2.4 L/min/m² limits its generalizability. Patients undergoing CPB often have comorbidities and suboptimal perfusion. Future studies should evaluate PvCO2 × Ve/Q in broader clinical settings, including extreme conditions like profound hypothermia, prolonged CPB, or the use of vasopressors and blood transfusions, which could affect CO2 and lactate levels and warrant further analysis.