It 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 splenomegaly 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
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 ultrasonographically measured organ thickness at the region of the hilus.1,4 Despite these previous reports, the magnitude of drug-induced changes on splenic size remains controversial. The mechanisms of drug-induced splenic dilation or constriction are complex and beyond simple local smooth muscle reactivity, and they are not fully understood. It is difficult to interpret results of previous 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 images rapidly with little stress to patients. In humans, CT is accepted as an accurate tool to measure organ volume6 by providing high-resolution images that are spatially accurate.7 Volume can be calculated by determining the area of an organ on each CT slice, multiplying the area by the slice thickness, and adding the volume of all slices.8 The use of CT volumetry provides an opportunity to noninvasively study the effects of anesthetic drugs on splenic volume. The lack of potentially stressful interaction with patients helps investigators avoid or diminish catecholamine release, which may interfere with baseline measurements and the apparent effect of drugs. An additional benefit of this technique is the ability to acquire volume data without general anesthesia because of the rapid image acquisition afforded by modern multislice helical CT scanners, which further minimizes factors that could influence splenic volume. The purpose of the study reported here was to use CT to measure changes in splenic volume caused by commonly used sedative and anesthetic drugs in dogs.
Excel, Microsoft Office 2007, Microsoft Corp, Redmond, Wash.
Boehringer Ingelheim Vetmedica Inc, St Joseph, Mo.
Abbott Laboratories Inc, Chicago, Ill.
Propoflo, Abbott Animal Health, Chicago, Ill.
Hydromorphone HCl, Westward Pharmaceuticals, Eatontown, NJ.
Dexdomitor, Pfizer Animal Health, Madison, NJ.
GE BrightSpeed Elite 16-slice, General Electric, Fairfield, Conn.
Mimics x64, version 14, Materialise, Plymouth, Mich.
PROC GLM, SAS, version 9.2, SAS Institute Inc, Cary, NC.
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