Right-to-left shunt

Abstract

A right-to-left shunt occurs when a part of the venous blood short-circuits the pulmonary alveoli and directly passes into the systemic circulation. Normally a part of mediastinal, portal, bronchial and myocardial venous blood flows into the left cavities resulting in a physiologic shunt, about 1 to 2% of the cardiac output. In pathologic conditions, much greater shunts may be encountered: extrapulmonary shunts due to congenital cardiac malformation, congenital or acquired pulmonary fistula, specially in liver cirrhosis, intra pulmonary atelectasis, acute edema or pneumopathy [1]. It is important to identify the right-to-left shunt because it is responsible for oxygenotherapy resistant hypoxemia. Shunt is often associated with other respiratory or circulatory disorders and often occurs in very debilitated patients. Thus, a specific and noninvasive diagnostic procedure is required.