Figure 4. Receiver-operator characteristic curve for upper sensory level obtained 10 min after the first 2.5 mg isobaric bupivacaine injection to predict maldistribution. The area under the receiver-operator characteristic curve is 0.98 +/- 0.04. For a given upper sensory level, the abscissa value is the ratio of the number of maldistributions occurring in patients with an upper sensory level greater or equal to this threshold to the number of maldistributions occurring in all patients. No maldistribution occurred if the upper sensory level was greater or equal to L3 in the isobaric group.