Retrospective Assessment of the Oxygenation Index in Dogs Undergoing Mechanical Ventilation for Primary Pulmonary Parenchymal Disease

OBJECTIVE: To assess the association between the oxygenation index (OI) and survival in mechanically ventilated dogs with primary pulmonary parenchymal disease. DESIGN: Retrospective, multicenter study. SETTING: Three veterinary medical teaching institutions and one private veterinary referral center. ANIMALS: Seventy-nine client-owned dogs. INTERVENTIONS: None. METHODS: (PF) ratio were calculated for dogs undergoing mechanical ventilation for primary pulmonary disease. Median OI was lower in survivors (2.6) than nonsurvivors (6.6; p < 0.001), while PF was higher in survivors (317.9 vs. 177.9; p < 0.001). OI predicted mortality with an area under the receiver operating characteristic curve of 0.73, sensitivity of 65%, and specificity of 80% at an optimal cutoff of 4.3. Median PF had an area under the receiver operating characteristic curve of 0.72, sensitivity of 70%, and specificity of 73% at an optimal cutoff of 237.8. Each 1-unit increase in OI was associated with a 35% higher mortality risk (odds ratio: 1.35; 95% confidence interval: 1.14-1.61). Survivors showed greater improvement in OI during ventilation (p = 0.004). Using Pediatric Acute Lung Injury Consensus Conference and pediatric acute respiratory distress syndrome thresholds, survival likelihood declined with increasing severity, with no survivors in the severe category (OI >16). Similar trends were observed using updated Pediatric Acute Lung Injury Consensus Conference-2 criteria and acute respiratory distress syndrome severity classifications. CONCLUSIONS: Higher OI values and lower PF ratios were associated with mortality in this group of mechanically ventilated dogs, with both metrics demonstrating similar predictive accuracy. Results suggest species-specific OI and PF thresholds are needed.