Fig. 5. Box plots of Pearson correlation coefficients between waveform variables and the steps of blood withdrawal. The line across the box indicates the median. The box represents the interquartile range (the difference between the 75th and 25th percentiles), which contains 50% of the values. The whiskers are lines that extend from the box to the highest and lowest values, excluding outliers (cases with values > 1.5 box lengths from the upper or lower edge of the box ). The marked ID of patients indicate those with nonsignificant correlation. dPOP = pulse oximetry waveform amplitude; PPV = pulse pressure variation; PWV = plethysmographic waveform variation; SPV = systolic pressure variations.