Comparison of different dynamic indices of preload. Box-and-whisker plots and individual values (open circles) of respiratory variations of brachial peak velocity (ΔVpeakbrach), radial arterial pulse pressure variation (ΔPPrad) and stroke volume variation measured using the FloTrac/Vigileo monitoring system (ΔSVVigileo) before volume expansion (VE), in responder (R, stroke volume index (SVi) ≥15% after VE) and nonresponder (NR, SVi <15% after VE) patients. The central box represents the values from the lower to upper quartile (25th to 75th percentile). The middle line represents the median. A line extends from the minimum to the maximum value.