A patient with recent abdominal surgery is at high risk for venous thromboembolism due to immobilization and inflammatory changes that promote clot formation. Sudden onset of dyspnea and hypoxia postoperatively strongly suggests pulmonary embolism (PE), which can cause rapid cardiopulmonary compromise and requires immediate diagnosis and treatment. Other causes like pneumonia or atelectasis develop more gradually and are less likely to present with acute hypoxia. Prompt recognition and management of PE are critical to reducing mortality in postoperative patients.

Reference: Harrison's Principles of Internal Medicine, Jameson et al., 20th Edition.