My morphine pumps have failed a few times resulting in withdrawal. When It was removed I went into full blown withdrawal. Several on this forum have had similar experiences. Thats because the pump was my only source of narcotic. So, in my situation some did go systemic. That only makes sense since the pain receptors are are in the brain and other areas that might not be where the pain is issuing from. So the narcotic has to eventually reach those receptors areas from the pain producing area to be effective and that means traveling to those receptor areas. Those receptors become greedy for the constant supply of morphine and when it is stopped that is when withdrawal sets in. Overly simplified and in layman's term, but I believe you get the point. Also, many anesthesiologists know this delivery system can result in dependence.