Effects of continuous epidural administration of bupivacaine through a catheter in pigs

We studied whether long-term epidural catheter (nylon) placement for bupivacaine administration (morphine in 2 pigs) would cause any pathological changes in the epidural space and spinal cord of pigs. There were similar kinds of slight inflammatory changes in ligamentum flavum and dura mater in bupivacaine-treated (4 ml 0.5% bupivacaine, twice daily for 7 days, n = 8; 16 ml 0.25% bupivacaine infusion in 12 h, n = 3) and morphine-treated (2 mg preservative-free morphine, twice daily for 7 days, n = 2) pigs compared with corresponding control pigs (saline, n = 8) 24 h after treatment. There were minimal inflammatory changes in one of the two bupivacaine-treated pigs recovering for 3 weeks. In one of the bupivacaine pigs there was a bacterial infection (Staphylococcus aureus) all along the epidural catheter. In this pig the overall level of bupivacaine plasma concentrations after an injection decreased stepwise during the 7-day period (sampling at 2-day intervals). In the other pigs treated for 7 days, the level of bupivacaine concentrations did not change markedly from first sampling to later samplings. It is probable that inflammatory changes in the epidural space, following prolonged administration of bupivacaine and morphine, are largely due to catheter irritation.