Effects of cardiogenic shock on lactate and glucose metabolism after heart surgery

Background: Hyperlactatemia is a prominent feature of cardiogenic shock. It can be attributed to increased tissue production of lactate related to dysoxia and to impaired utilization of lactate caused by liver and tissue underperfusion. The aim of this prospective observational study was to determine the relative importance of these mechanisms during cardiogenic shock.

Patients: Two groups of subjects were compared: seven cardiac surgery patients with postoperative cardiogenic shock and seven healthy volunteers.

Methods: Lactate metabolism was assessed by using two independent methods: a) a pharmacokinetic approach based on lactate plasma level decay after the infusion of 2.5 mmol·kg^-1 of sodium lactate; and b) an isotope dilution technique for which the transformation of [¹³C]lactate into [¹³C]glucose and ¹³CO₂ was measured. Glucose turnover was determined using 6,6²H₂-glucose.

Results: All patients suffered from profound shock requiring high doses of inotropes and vasopressors. Mean arterial lactate amounted to 7.8 ± 3.4 mmol·L^-1 and mean pH to 7.25 ± 0.07. Lactate clearance was not different in the patients and controls (7.8 ± 3.4 vs. 10.3 ± 2.1 mL·kg^-1·min^-1). By contrast, lactate production was markedly enhanced in the patients (33.6 ± 16.4 vs. 9.6 ± 2.2 μmol·kg^-1·min^-1;p < .01). Exogenous [¹³C]lactate oxidation was not different (107 ± 37 vs. 103 ± 4 mmol), and transformation of [¹³C]lactate into [¹³C]glucose was not different (20.0 ± 13.7 vs. 15.2% ± 6.0% of exogenous lactate). Endogenous glucose production was markedly increased in the patients (1.95 ± 0.26 vs. 5.3 ± 3.0 mg·kg^-1·min^-1;p < .05 [10.8 ± 1.4 vs. 29.4 ± 16.7 μmol·kg^-1·min^-1]), whereas net carbohydrate oxidation was not different (1.7 ± 0.5 vs. 1.3 ± 0.3 mg·kg^-1·min^-1 [9.4 ± 2.8 vs. 7.2 ± 1.7 μmol·kg^-1·min^-1]).

Conclusions: Hyperlactatemia in early postoperative cardiogenic shock was mainly related to increased tissue lactate production, whereas alterations of lactate utilization played only a minor role. Patients had hyperglycemia and increased nonoxidative glucose disposal, suggesting that glucose-induced stimulation of tissue glucose uptake and glycolysis may contribute significantly to hyperlactatemia.