Associations between oxygen delivery and cardiac index with hyperlactatemia during cardiopulmonary bypass

Metabolism management plays an essential role during cardiopulmonary bypass (CPB). There are different metabolic management devices integrated to heart-lung machines; the most commonly used and accepted metabolic target is indexed oxygen delivery (DO_2i) (280 mL/min/m²) and cardiac index (CI) (2.4 L/min/m²), which can be managed independently or according to other metabolic parameters. Our objective was to compare lactate production during CPB procedures using different metabolic management: DO_2i in relation to indexed oxygen extraction ratio (O₂ER_i) and CI in relation to mixed venous oxygen saturation (SvO₂).

Data on 500 CPB procedures were retrospectively collected in a specialized regional tertiary cardiac surgery center in Italy between September and 2012 and November 2019. In group A, the DO_2i with 280 mL/min/m² target in relation to O₂ER_i 25% was used; in group B, CI with 2.4 L/min/m² target in relation to SvO₂ 75% was used. During CPB, serial arterial blood gas analyses with blood lactate and glucose determinations were obtained. Hyperlactatemia (HL) was defined as a peak arterial blood lactate concentration >3 mmol/L. The postoperative outcome of patients with or without HL was compared.

Eight pre- and intraoperative factors were found to be significantly associated with peak blood lactate level during CPB at univariate analysis. HL (>3 mmol/L) was detected in 15 (6%) patients of group A and in 42 (16.8%) patients of group B (P = .022); hyperglycemia (>160 mg/dL) was found in 23 (9.2%) patients of group A and in 53 (21.2%) patients of group B (P = .038). Patients with HL during CPB had a significant increase in serum creatinine value, higher rate of prolonged mechanical ventilation time and intensive care unit stay. A cutoff of DO_2i <270 mL/min/m² in relation to O₂ER_i >35% in group A and a cutoff of CI <2.4 L/min/m² in relation to SvO₂ <65% in group B were found to have a positive predictive value of 80% and 75% for HL, respectively. A cutoff of DO_2i >290 mL/min/m² in relation to O₂ER_i 24% in group A and a cutoff of CI >2.4 L/min/m² in relation to SvO₂ >75% in group B were found to have a negative predictive value of 78% and 62% for HL, respectively.

This retrospective observational analysis showed that management of DO_2i in relation to O₂ER_i was 16% more specific in terms of negative predictive value for HL during CPB compared with the use of CI in relation to SvO₂. Group A reported a significant reduction in the incidence of intraoperative lactate peak, correlated with postoperative reduction of serum creatinine value, mechanical ventilation time, and intensive care unit stay, compared with group B.