Adverse Reactions in Horses that Underwent General Anesthesia and Cervical Myelography

Background: The study was prompted by a perceived high prevalence of myelographic complications varying in severity and type, and attributed to the contrast material or the procedure. Hypotheses: 1. Any adverse reaction (AAR) is associated with a change in CSF volume induced either by removal of CSF or addition of contrast material. 2. AAR occurs more frequently in horses with higher premyelography neurologic grade. 3. Nonspecific hyperthermia is attenuated by anti-inflammatory and osmotic agents. Animals: Horses (n = 278) that underwent myelography between 2000 and 2012 at 5 institutions: A (87), B (68), C (65), D (46), and E (12). Methods: Multi-institutional, retrospective, observational cross-sectional study. Results: AAR were observed in 95/278 (34%) horses, were associated with longer general anesthesia time (P =.04) and higher contrast-medium volume (P =.04); euthanasia because of AAR was performed in 5/278 (2%) horses. Adverse neurologic reactions were the most common type of complication observed occurring in 15/278 (5%) and 42/235 (18%) of horses in the intra-and postmyelography periods. A relationship between AAR and premyelography neurologic grade was not identified (P =.31). Nonspecific hyperthermia was observed in 25/235 (11%) horses; no relationship was observed with administration of anti-inflammatory drugs and osmotic agents (P =.30). Conclusions and clinical importance: The category of AAR occurred in one-third of the horses generally was mild and self-limiting. These reactions were associated with increased contrast-medium volume and longer anesthesia time; but, no specific procedural recommendations could be made because of small odds ratios (OR) of < 2 for each 1 mL increase in contrast material and for each 1 minute of additional anesthesia time.