Fig. 8. Simulation of the cumulative amount of opioid (percent dose) that is cleared over time into the systemic circulation via  the spinal cord (dotted line) or the epidural space (straight line). The amounts are the sum of the predicted amount in the L2–L3 and T11 compartments. The median for morphine and sufentanil and the geometric mean for alfentanil and fentanyl of the estimated model parameters were used to simulate the profiles for each drug.