Fig. 2. Cerebrospinal fluid concentrations in the horizontal and vertical groups for bupivacaine (A, B ) and baclofen (C, D ). Data points are averages, and error bars  are omitted for clarity. The average of the last five data points (280–360 min) from each probe site was used to calculate the steady-state concentration of each drug in both groups. Values equal to zero are omitted to permit use of log-scale.