The V-line: a sonographic aid for the confirmation of pleural fluid

In this short report, we describe the sonographic observation of the vertebral or ‘V-line’ to help confirm the presence of pleural fluid in the supine patient. The V-line sign is a result of the fluid acting as an acoustic window to enable visualization of vertebral bodies and posterior thoracic wall, thus confirming the presence of pleural fluid.The V-line is a useful sonographic sign to aid the diagnosis of pleural free fluid.The use of ultrasound for the detection of pleural fluid is reliable when correctly identified [1]. Pleural free fluid is common in patients presenting to hospital with respiratory symptoms. In one study of 880 patients presenting to emergency departments in North America and Europe with a chief complaint of shortness of breath, 17% were found to have pleural effusions [2]. As many as 62% of patients requiring admission to medical intensive care units (ICU) have pleural effusions [3], and between 10% to 20% [4-10] of patients presenting with thoracic trauma have hemothorax. Abnormal accumulation of fluid in the pleural cavity occurs when there is an imbalance between production and absorption, resulting from a variety of disease processes including, but not limited to, malignancy, heart failure, pneumonia, empyema, and traumatic bleeding. Fluid accumulation in the pleural cavity ultimately leads to lung compression and abnormalities in oxygenation or ventilation. The presence of pleural fluid is typically diagnosed through physical examination and plain radiography. Classic physical exam findings of pleural fluid have extremely poor sensitivities and specificities for the diagnosis of pleural fluid and should not be relied on for diagnosis [11].Chest X-ray (CXR), the most commonly used radiographic modality to detect pleural effusion, is able to detect only relatively large effusions. Studies have shown that over 175 mL of fluid is required to cause blunting of the costophrenic angles in an upright CXR [12]. Supine CXR, used in critically ill