Mildly elevated lactate levels are associated with microcirculatory flow abnormalities and increased mortality: a microSOAP post hoc analysis

Namkje A. R. Vellinga, E. Christiaan Boerma, Matty Koopmans, Abele Donati, Arnaldo Dubin, Nathan I. Shapiro, Rupert M. Pearse, Peter H. J. van der Voort, Arjen M. Dondorp, Tony Bafi, Michael Fries, Tulin Akarsu-Ayazoglu, Andrius Pranskunas, Steven Hollenberg, Gianmarco Balestra, Mat van Iterson, Farid Sadaka, Gary Minto, Ulku Aypar, F. Javier Hurtado, Giampaolo Martinelli, Didier Payen, Frank van Haren, Anthony Holley, Hernando Gomez, Ravindra L. Mehta, Alejandro H. Rodriguez, Carolina Ruiz, Héctor S. Canales, Jacques Duranteau, Peter E. Spronk, Shaman Jhanji, Sheena Hubble, Marialuisa Chierego, Christian Jung, Daniel Martin, Carlo Sorbara, Jan Bakker, Can Ince, for the microSOAP study group

Mildly elevated lactate levels (i.e., 1-2 mmol/L) are increasingly recognized as a prognostic finding in critically ill patients. One of several possible underlying mechanisms, microcirculatory dysfunction, can be assessed at the bedside using sublingual direct in vivo microscopy. We aimed to evaluate the association between relative hyperlactatemia, microcirculatory flow, and outcome. This study was a predefined subanalysis of a multicenter international point prevalence study on microcirculatory flow abnormalities, the Microcirculatory Shock Occurrence in Acutely ill Patients (microSOAP). Microcirculatory flow abnormalities were assessed with sidestream dark-field imaging. Abnormal microcirculatory flow was defined as a microvascular flow index (MFI) < 2.6. MFI is a semiquantitative score ranging from 0 (no flow) to 3 (continuous flow). Associations between microcirculatory flow abnormalities, single-spot lactate measurements, and outcome were analyzed. In 338 of 501 patients, lactate levels were available. For this substudy, all 257 patients with lactate levels ≤ 2 mmol/L (median [IQR] 1.04 [0.80-1.40] mmol/L) were included. Crude ICU mortality increased with each lactate quartile. In a multivariable analysis, a lactate level > 1.5 mmol/L was independently associated with a MFI < 2.6 (OR 2.5, 95% CI 1.1-5.7, P = 0.027). In a heterogeneous ICU population, a single-spot mildly elevated lactate level (even within the reference range) was independently associated with increased mortality and microvascular flow abnormalities. In vivo microscopy of the microcirculation may be helpful in discriminating between flow- and non-flow-related causes of mildly elevated lactate levels. ClinicalTrials.gov, NCT01179243 . Registered on August 3, 2010.