Retrospective analysis of carboxyhemoglobin and methemoglobin levels and their association with pneumonia severity in dogs.

Bacterial pneumonia in dogs is a severe respiratory disease, and, currently, veterinary medicine lacks robust, evidence-based tools for assessing its severity, unlike those available in human medicine. While co-oximetry has been useful in diagnosing some respiratory diseases in humans, its application in veterinary medicine remains limited. This retrospective study aimed to assess carboxyhemoglobin (COHb), methemoglobin (MetHb), oxyhemoglobin (O2Hb), and deoxyhemoglobin (HHb) levels in 30 dogs diagnosed with bacterial pneumonia compared to 42 control dogs without respiratory conditions, and to correlate these levels with key clinical indicators, including length of hospital stay, and the PaO₂/FiO₂ ratio. Analysis of arterial blood revealed significant differences between groups: dogs with pneumonia exhibited lower levels of COHb (p = 0.047), MetHb (p = 0.008), and O2Hb (p < 0.001), alongside higher levels of HHb (p < 0.001). However, no significant correlations were observed between these biomarkers and hospital stay duration or the PaO₂/FiO₂ ratio. Among pneumonia patients, the mortality rate was 23.3%, and hospital stays ranged from 2 to 7 days. These results indicate that, although the biomarkers reflect alterations in oxygen transport, they are not reliable predictors of prognosis in canine bacterial pneumonia. This study underscores the necessity for prospective investigations with larger samples and a multifactorial approach that combines biomarkers with clinical, radiological, and laboratory parameters to enhance the management of this complex condition.