Evaluating the ratio of arterial partial pressure of oxygen to inspired oxygen fraction and dynamic compliance following anesthetic induction for predicting postanesthetic hypoxemia in dogs.

Abstract

Objective: To evaluate correlation between postanesthetic induction ratio of arterial partial pressure of oxygen to inspired oxygen fraction (PaO₂:FIO₂) and dynamic compliance (C_dyn) with postanesthetic hypoxemia [PaO₂ < 80 mmHg (10.7 kPa)] in mechanically ventilated dogs, and to compare PaO₂:FIO₂ and C_dyn for predicting postanesthetic hypoxemia.

Study design: Retrospective, single-cohort, observational study.

Animals: A total of 168 dogs anesthetized with isoflurane under pressure-controlled ventilation.

Methods: Postinduction arterial blood gas (ABG) analysis was performed 5-40 minutes postintubation and following postextubation (room-air). C_dyn values were matched to the nearest postinduction ABG measurement (within 15 minutes). PaO₂:FIO₂ and C_dyn values were categorized using thresholds of 300 mmHg (40.0 kPa) and 400 mmHg (53.3 kPa), and 1.0 and 1.5 mL cmH₂O^-1 kg^-1. Linear-by-linear association was used to evaluate PaO₂:FIO₂ and C_dyn with the prevalence of postanesthetic hypoxemia. Diagnostic accuracy of these variables was assessed using receiver operating characteristic (ROC) curve analysis. Optimal cut-off values for distinguishing hypoxemia were determined using the empirical quantile bootstrap method (fixed sensitivity of 95%).

Results: Postanesthetic hypoxemia was observed in 22/168 dogs. Lower postinduction PaO₂:FIO₂ (p = 0.033) and C_dyn (p = 0.002) values were associated with a significantly higher prevalence of postanesthetic hypoxemia. The area under the ROC curve (AUC) of PaO₂:FIO₂ {0.696 [95% confidence interval (CI): 0.599-0.807]} and C_dyn [0.716 (95% CI 0.602-0.824)] exhibited good (AUC 0.6-0.7) to satisfactory (AUC 0.7-0.8) diagnostic accuracy, with no significant difference between variables (p = 0.432). Optimal cut-off values were 332.80 mmHg (44.4 kPa) (95% CI 274.41-374.52 mmHg, 36.6-49.9 kPa) for PaO₂:FIO₂ and 1.01 (95% CI 0.86-1.13) mL cmH₂O^-1 kg^-1 for C_dyn.

Conclusions and clinical relevance: Postanesthetic hypoxemia was more frequently observed in dogs with low postinduction PaO₂:FIO₂ and C_dyn. These variables had good to satisfactory diagnostic accuracy.