 3. STUDY OF MICROCIRCULATION In 25 patients, functional capillary density FCD microvascular flow index MFI, proportion of perfused vessels PPV and microvascular heterogeneity index MHI will be measured with a side-stream dark-field SDF camera at five time points: 1Baseline, 2 At the end of the fluid challenge 4 ml kg in 5 minutes, 3 5 minutes after the end of the fluid challenge, 4 10 minutes after the end of the fluid challenge, 5 15 minutes after the end of the fluid challenge. 