This text outlines a structured approach to diagnose and manage hypoxemia in dogs and cats using pulse oximetry and arterial blood gas (ABG) analysis. It details the main causes—low FiO2, hypoventilation, and venous admixture—and explains how tools like the A–a gradient, partial pressure of oxygen/FiO2 ratio, and respiratory-rate oxygenation index help assess severity and guide therapy. Stepwise ABG interpretation is emphasized to tailor oxygen support, from conventional methods to high-flow oxygen therapy or mechanical ventilation in severe cases. Continuous monitoring improves prognosis and informs escalation of care.