Distribution of epidural lipophilic and hydrophilic opioids

This figure shows the purported mechanisms actions of epidural lipophilic and hydrophilic opioids. The thickness of the arrows reflects the relative importance of the route or effect. Note that addition of epinephrine to the epidural solution can reduce vascular uptake of lipophilic opioids and increased penetration of the dura-arachnoid, leading to a local spinal effect and improved analgesia.