Lung ultrasound for diagnosing pulmonary embolism

Pulmonary embolism (PE) remains a challenge for any physician because its clinical presentation covers a broad spectrum and is often similar to other cardio-pulmonary disorders. PE is still under-diagnosed due to it’s various/atypical clinical presentations, the dynamic of embolic processes and due to the fact that we have several diagnostic methods without 100% sensitivity and specificity. About 5% of patients with acute PE suffer from circulatory collapse without comorbidity, about 10% from syncope with cardiovascular comorbidity, about 25% from isolated dyspnea and about 60% from pleuritic pain and/or hemoptysis [1, 2]. According to the ERC guidelines, PE is stratified for high (>15%), intermediate (3-1%) and low (<1%) mortality risk [3]. Patients with high mortality risk reveal shock or hypotension, those with intermediate risk show right ventricular dysfunction or myocardial injury, whereas patients with low risk have no evidence of these symptoms [3]. However, it has been demonstrated that the outcome of PE depends on the size of the emboli as well as on comorbidity [4]. The dynamic of embolic processes is characterised by incomplete and complete infarctions. Incomplete infarctions may disappear completely within 2 to 4 days, in accordance with resolution of the intra-alveolar haemorrhage [5]. Infarctions are visible by LUS as well as by CT [5]. Computed tomographic pulmonary angiography (CTPA) is regarded as the method of choice for diagnosing PE. Nevertheless, CTPA is limited by radiation dose, application of contrast medium and availability. Therefore, lung sonography (LUS), as a non-invasive technique, is recommended by German AWMF guidelines in patients with renal failure, pregnancy or contrast agent allergy [6]. Detection of thromboembolic lesions in the lung using ultrasound was first described by Joyner and Miller in 1966 [7, 8]. They created experimental PE in dogs and monitored changes in reflected ultrasound in the affected peripheral lung areas. In recent years, several studies have investigated the role of LUS in diagnosing PE [9-11].