Fig. 2From: Optimization of programmed intermittent epidural bolus volume for different concentrations of ropivacaine in labor analgesia: a biased coin up-and-down sequential allocation trialIndividual responses of women to different programmed intermittent epidural bolus (PIEB) volumes in group A. Open circle: ineffective PIEB volume; Filled circle: effective PIEB volumeBack to article page