<qa>  What is the percentage of perfused vessels?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. 