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Objectives: 1) Describe the clinical course and diagnostic findings of cats with histopathologic evidence of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). 2) Identify risk factors for ALI/ARDS in cats.

Animals: Sixty-five client-owned cats with moderate to severe interstitial pneumonia, pneumonitis or alveolitis consistent with ALI/ARDS on post-mortem examination and clinical evidence of respiratory compromise.

Procedure: Retrospective evaluation of medical records, postmortem examination and radiographs.

Results: Cats in this study tended to be middle aged (mean 6.5±4.9 years). They had a short duration of illness (median 4 days; range 0–120 days) and of dyspnea (median 1 day; range 1–7 days). On presentation, the cats were tachypneic (mean respiratory rate 53±23 bpm) and relatively bradycardic (mean heart rate 166±43 bpm). The majority of cats were dyspneic (n=39) at presentation; all others developed respiratory difficulties during hospitalization. The mean white blood cell count was within normal limits (14.6±14.0 k/μL); 8 cats had a leukocytosis and 7 were leucopenic. Clinical findings consistent with SIRS (n=39) and sepsis (n=10) were common. Thoracic radiographs were reviewed in 31 cats and alveolar disease was the most frequent pattern (105 lung lobes) followed by interstitial disease (86 lung lobes). No cat had normal thoracic radiographs throughout hospitalization. Underlying disease was not identified on post-mortem examination in 15 cats (23%), but in the remaining cats underlying diseases included infectious systemic disease (n=11), neoplasia (n=8), respiratory (n=8) and urinary (n=7) system disorders, acute pancreatitis (n=7), hepatic diseases (n=5), major trauma (n=4), sepsis (n=3), CNS (n=2) and other systems (n=5). Nine cats had more then one underlying process.

Conclusions: This study describes a naturally-occurring syndrome of ALI/ARDS in cats analogous to that which occurs in dogs and humans. In cats, ALI/ARDS occurs as a sequela of a variety of underlying systemic diseases, but in approximately one-quarter of patients an underlying cause is not identified at necropsy. It is important to consider ALI/ARDS in systemically ill cats who become dyspneic; in cats with pulmonary disease with acute worsening of respiratory status and in cats with pulmonary infiltrates for which no other cause can be identified.