Effects of cardiogenic shock on lactate and glucose metabolism after heartsurgery

Background: Hyperlactatemia is a prominent feature of cardiogenic shock. It can be attributed to increased tissue production of lactate related to dys oxia and to impaired utilization of lactate caused by liver and tissue unde rperfusion, The aim of this prospective observational study was to determin e the relative importance of these mechanisms during cardiogenic shock. Patients: Two groups of subjects were compared: seven cardiac surgery patie nts 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 dilutio n technique for which the transformation of [C-13]lactate into [C-13]glucos e and (CO2)-C-13 was measured. Glucose turnover was determined using 6,6(2) H(2)-glucose. Results: All patients suffered from profound shock requiring high doses of inotropes and vasopressors. Mean arterial lactate amounted to 7.8 +/- 3.4 m mol . 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) . m in(-1)). By contrast, lactate production was markedly enhanced in the patie nts (33.6 +/- 16.4 vs. 9.6 +/- 2.2 mu mol . kg(-1) . min(-1); p < .01), Exo genous [C-13]lactate oxidation was not different (107 +/- 37 vs. 103 +/- 4 mmol), and transformation of [C-13]lactate into [C-13]glucose was not diffe rent (20.0 +/- 13.7 vs, 15.2% +/- 6.0% of exogenous lactate), Endogenous gl ucose 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 mu mol . kg(-1) min(-1)]), whereas net carbohydrate oxidation was not diffe rent (1.7 +/- 0.5 vs, 1.3 +/- 0.3 mg . kg(-1) . min(-1) [9.4 +/- 2.8 vs. 7. 2 +/- 1.7 mu mol . kg(-1) . min(-1)]). Conclusions Hyperlactatemia in early postoperative cardiogenic shock was ma inly related to increased tissue lactate production, whereas alterations of lactate utilization played only a minor role. patients had hyperglycemia a nd increased nonoxidative glucose disposal, suggesting that glucose-induced stimulation of tissue glucose uptake and glycolysis may contribute signifi cantly to hyperlactatemia.