JAVMA, Vol 221, No. 1, July 1, 2002
ment would have been lost. Use of play-the-winner analyses allowed inclusion of long-term follow-up data for 12 dogs in which medical treatment failed and surgery was undertaken. In the present study, dogs that were euthanatized because of recurrence of pyothorax or treatment failure were classified as having died of pyothorax. This may have affected DFI, because different owners were likely committed to different levels of treatment. The issue of how, in these types of studies, to classify dogs that have been euthanatized is controversial. Two other methods of dealing with this problem have been proposed: exclusion of all animals that were euthanatized and classification of all dogs that were euthanatized as having died of causes unrelated to the underlying disease. Both of these methods are valid but have the disadvantage of decreasing the number of animals included in the study or of disregarding the likelihood that animals were euthanatized because of a perceived poor quality of life secondary to the underlying disease. For the present study, animals were included only if they had undergone surgery or had been treated medically for at least 2 days. Thus, dogs that were euthanatized within 24 hours after the initial examination were excluded. In addition, 1 dog that was euthanatized after 20 days of medical treatment was excluded from the study because the decision was made on the basis of financial concerns and not quality of life reasons. Given the low number of subjects and subsequent low power of some results, we cannot conclude that there is not a difference between treatment groups in regard to some of the variables evaluated.30 A multicenter study would help increase the number of cases but might increase the diversity of treatment modalities. A prospective multicenter study with standardized treatment protocols would be ideal in evaluating risk factors and DFI following medical versus surgical treatment of pyothorax. Data obtained at the time of the initial examination cannot be relied on solely to determine whether medical or surgical treatment should be performed, and overall clinical assessments should be considered. In addition, results of the present study suggest that dogs with pyothorax that are treated surgically have a better prognosis and longer DFI than dogs treated medically. Furthermore, surgical intervention should be considered if there is radiographic evidence of mediastinal or pulmonary lesions or if Actinomyces organisms are isolated from the pleural fluid. a
Statview, SAS Institute Inc, Cary, NC. Solo power analysis, BMDP Statistical Software, Los Angeles, Calif.
b
References 1. Frendin J. Pyogranulomatous pleuritis with empyema in hunting dogs. Zentralbl Veterinarmed [A] 1997;44:167–178. 2. Piek CJ, Robben JH. Pyothorax in nine dogs. Vet Q 2000;22:107–111. 3. Robertson SA, Stoddart ME, Evans RJ, et al. Thoracic empyema in the dog: a report of twenty-two cases. J Small Anim Pract 1983;24:103–119. 4. Turner WD, Breznock EM. Continuous suction drainage for management of canine pyothorax—a retrospective study. J Am Anim Hosp Assoc 1988;24:485–494. Scientific Reports: Retrospective Study
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outcome. In many dogs in this study, the percentage of WBC that were band neutrophils was not excessive. Immature neutrophils have been reported as an indicator of outcome in dogs with sepsis.24 However, dogs with pyothorax rarely have acute septicemia at the time of initial examination. It is possible that pyothorax is so slowly progressive that the body has time to heighten local and systemic immune responses. Thus, the bone marrow may maintain adequate production of neutrophils without releasing excessive numbers of premature forms into the circulation.25 Results of bacterial culture of pleural fluid samples were analyzed individually in the present study, as well as after grouping as aerobic or anaerobic and gram-positive or gram-negative. This was done to determine whether 1 group of bacteria was more pathogenic than another, influencing outcome. Anaerobic bacteria are thought to increase the severity of mixed bacterial infections,26 and gram-negative bacteria are considered highly pathogenic under certain conditions.27 However, no bacterial grouping was associated with DFI or outcome in the present study. Results of antimicrobial susceptibility testing of aerobic bacteria isolated from pleural fluid from dogs in the present study suggest that cefoxitin, enrofloxacin, and trimethoprim-sulfonamide would be good empirical choices for antimicrobial treatment while results of bacterial culture and susceptibility testing are pending. Of these 3, enrofloxacin has the best gram-negative spectrum and can be given IV. Antimicrobial susceptibility testing of anaerobic bacteria is difficult and expensive, but these bacteria generally are susceptible to a variety of antimicrobials, such as penicillin.26,28 Similarly, Actinomyces spp typically are susceptible to ampicillin.29 Thus, a combination of enrofloxacin and ampicillin may be considered the antimicrobial treatment of choice while results of bacterial culture and susceptibility testing are pending in dogs with pyothorax. Although enrofloxacin was commonly given IV in this study, it is not approved for IV administration in dogs. There are inherent limitations to retrospective studies. In particular, inclusion of results for dogs that were initially treated medically and underwent surgery after medical treatment was considered to have failed likely introduced some bias, so that dogs in the surgical treatment group may have been more severely affected than dogs in the medical treatment group. In addition, treatment (medical vs surgical) was not standardized but allocated at the attending clinician’s discretion. Thus, confounding effects cannot be ruled out. The play-the-winner study design has been used mainly in prospective studies, and in these studies, criteria are established in advance to decide when to change treatment. In the present study, we relied on the attending clinicians’ discretion to determine when to change from medical to surgical treatment. We elected to use the play-the-winner design to analyze results of the present study because it more accurately reflects the clinical setting,10-12 where treatment is often changed if the initial treatment fails. If a more traditional study design had been used to analyze data in the present study, data obtained after a change in treat-