An abnormal ventilationperfusion ratio (Qs/Qr) | NEET Based MCQ

An abnormal ventilationperfusion ratio (Qs/Qr) in the postoperative patient has been associated with 

A. Pulmonary thromboembolism 
B. Lower abdominal surgery 
C. Starvation 
D. The upright position

Answer A. Pulmonary thromboembolism

Abnormalities of ventilation-perfusion ratio result from the shunting of blood to a hypoventilated lung or from the ventilation of hypoperfused regions of lung tissue. When this imbalance is extreme, as following massive pulmonary thromboembolism, the effect is life-threatening hypoxemia. Other common predisposing factors in the postoperative patient that contribute to this maldistribution include the assumption of a supine position, thoracic and upper abdominal incisions, obesity, atelectasis, and reduced cardiac output.