Microcirculatory blood flow as a tool to select ICU patients eligible for fluid therapy

PURPOSE: The aim of this study is to assess the incidence of sublingual microcirculatory flow alterations, according to a predefined arbitrary cutoff value, in patients with “clinical signs of impaired organ perfusion”. Secondary endpoints were the changes in microvascular flow index (MFI), “clinical signs of impaired organ perfusion”, and stroke volume (SV) after fluid administration, and the differences between groups. METHODS: Prospective, single-center, observational study in a 22-bed mixed intensive care unit (ICU). Patients ≥18 years with invasive hemodynamic monitoring and “clinical signs of impaired organ perfusion” as the principal reason for fluid administration were included. Before and after fluid challenge, systemic hemodynamics and direct in vivo observation of the sublingual microcirculation with sidestream dark-field imaging were obtained. Microvascular flow index (MFI) <2.6 was predefined as abnormal. RESULTS: N = 50. At baseline, MFI <2.6 was present in 66 % of the patients. In these patients, MFI increased from 2.3 (2–2.5) at baseline to 2.5 (2.1–2.8) after fluid challenge (p = 0.003). This was accompanied by a reduction in the number of “clinical signs of impaired organ perfusion” from 2 (1–2) to 1 (0–2) (p < 0.001). However, in patients with MFI >2.6 at baseline, MFI and clinical signs changed insignificantly [2.8 (2.8–2.9) versus 2.8 (2.7–3), p = 0.45, respectively, 1 (1–2) versus 1 (1–2), p < 0.32]. These changes were not restricted to patients with a rise in SV ≥10 %. CONCLUSIONS: These data add to the understanding that noninvasive assessment of microvascular blood flow may help to identify patients eligible for fluid therapy, and to evaluate its effect. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00134-012-2793-8) contains supplementary material, which is available to authorized users.