AJVR, Vol 73, No. 11, November 2012 1715 I t is important to understand the effects of commonly used sedatives and anesthetic drugs on splenic size. Iatrogenic splenic enlargement may complicate surgical access to the abdomen and possibly increase the chance of accidental splenic laceration. Drug-induced spleno- megaly may lead to the misdiagnosis of splenic disease because generalized splenomegaly can result from a variety of pathological causes, including neoplasia, rickettsial disease, passive congestion, extramedullary hematopoesis, and hypersplenism. 1,2 Effects of anesthetic drugs on canine splenic volume determined via computed tomography Caroline F. Baldo, DVM, PhD; Fernando L. Garcia-Pereira, DVM, MS; Nathan C. Nelson, DVM; Joe G. Hauptman, DVM, MS; Andre C. Shih, DVM Objective—To evaluate effects of commonly used anesthetics administered as single bo- lus injections on splenic volume. Animals—10 adult Beagles. Procedures—A randomized crossover study was conducted. Computed tomography was performed on dogs to determine baseline splenic volume and changes after IV injection of assigned drug treatments. Dogs were allowed to acclimate for 10 minutes in a plastic crate before acquisition of abdominal CT images. Treatments were administered at 7-day inter- vals and consisted of IV administration of saline (0.9% NaCl) solution (5 mL), acepromazine maleate (0.03 mg/kg), hydromorphone (0.1 mg/kg), and dexmedetomidine (0.005 mg/kg) to all 10 dogs; thiopental (8 mg/kg) to 5 of the dogs; and propofol (5 mg/kg) to the other 5 dogs. Splenic volume was calculated from the CT images with image processing software. A repeated-measures ANOVA was performed, followed by a Bonferroni post hoc test. Results—No significant difference in splenic volume was detected between the aceproma- zine, propofol, and thiopental treatments, but splenic volume was greater with these drugs than with saline solution, hydromorphone, and dexmedetomidine. Splenic volume was less with hydromorphone, compared with dexmedetomidine, but splenic volume with hydro- morphone and dexmedetomidine did not differ significantly from that with saline solution. Conclusions and Clinical Relevance—Administration of acepromazine, thiopental, and propofol resulted in splenomegaly. Dexmedetomidine did not alter splenic volume. Hydro- morphone slightly decreased splenic volume. Propofol should not be used when spleno- megaly is not desirable, whereas hydromorphone and dexmedetomidine may be used when it is best to avoid splenic enlargement. (Am J Vet Res 2012;73:1715–1719) The effects of drugs on splenic size have long been recognized. The effects of barbiturates on the spleen were first reported in dogs. 3 In that study, splenic size was subjectively evaluated on abdominal radiographs, which revealed splenomegaly 20 to 30 minutes after IV administration of 30 mg of thiopental sodium/kg. More recently, investigators directly measured splenic size after splenectomy in Beagles and ultrasonographi- cally measured organ thickness at the region of the hi- lus. 1,4 Despite these previous reports, the magnitude of drug-induced changes on splenic size remains contro- versial. The mechanisms of drug-induced splenic dila- tion or constriction are complex and beyond simple local smooth muscle reactivity, and they are not fully understood. It is difficult to interpret results of previ- ous studies because of differences in target drugs, lack of baseline values, use of inaccurate 2-D techniques as measurement tools, and the combination of anesthesia and surgical stimulation, which have opposing effects on splenic volume. 5 Computed tomography can be used to obtain im- ages rapidly with little stress to patients. In humans, CT is accepted as an accurate tool to measure organ volume 6 by providing high-resolution images that are spatially accurate. 7 Volume can be calculated by deter- Received October 12, 2011. Accepted December 2, 2011. From the Departments of Large Animal Clinical Sciences (Baldo) and Small Animal Clinical Sciences (Garcia-Pereira, Nelson, Haupt- man), College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824; and the Department of Large Animal Clini- cal Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32608 (Shih). Presented in part as an oral presentation during the 17th Internation- al Veterinary Emergency and Critical Care and American College of Veterinary Anesthesia Conference, Nashville, Tenn, September, 2011. Supported by Michigan State University startup funds provided to Dr. Garcia-Pereira. Address correspondence to Dr. Garcia-Pereira (fgarcia@cvm.msu. edu).