Systemic and local effects associated with long-term epidural catheterization and morphine-detomidine administration in horses.

OBJECTIVE The purpose of this study was to determine the systemic and local effects associated with long-term epidural catheterization and epidural morphine-detomidine administration in horses. STUDY DESIGN Development of systemic or local effects was assessed by placing caudal epidural catheters in study horses and administering injections through the catheters every 12 hours for 14 days. ANIMALS Ten horses with epidural catheters that received daily injections; six uncatheterized horses presented for euthanasia. METHODS Horses received either 0.2 mg/kg morphine sulfate and 30 micrograms/kg detomidine hydrochloride or an equivalent volume of physiologic saline solution through epidural catheters. Systemic effects were compared between control and treatment horses by measuring physical parameters and hay and water consumption, as well as by evaluating major organs after euthanasia. Local effects were studied by examining cerebrospinal fluid and by grading representative samples of the spinal cord and surrounding tissues histologically for inflammation and fibrosis. Local effects were compared between control and treatment horses, as well as between catheterized (control plus treatment) horses and uncatheterized horses. RESULTS No significant difference was identified in daily variables or hay and water consumption between control and treatment horses. No growth was obtained from cerebrospinal fluid cultures. No significant difference in cerebrospinal fluid values or spinal tissue inflammation or fibrosis grades was shown between control and treatment horses. However, when compared with uncatheterized horses, cerebrospinal fluid red blood cell values were marginally higher and protein concentrations were significantly higher in the catheterized group. Lumbosacral and sacral spinal tissue segment inflammation grades, and sacral segment fibrosis grades were significantly higher in catheterized horses. CONCLUSIONS Long-term epidural administration of a morphine-detomidine combination is not associated with apparent adverse systemic effects in horses. Localized inflammation and fibrosis seem to be catheter-related. CLINICAL RELEVANCE Potential systemic and local effects are important considerations with long-term administration of a morphine-detomidine combination through indwelling epidural catheters for alleviation of chronic musculoskeletal pain in horses.