Ultrasound at the pulmonary air-tissue interface: Mechanism of haemorrhage induction and implications for safe use of diagnostic and therapeutic lung ultrasound applications

Despite the high-diagnostic value of sonographic lung imaging, providing substantial patient benefit, clinician should be aware that ultrasound exposure on lung is not absolutely without risk of harm. As shown in animal models, lung ultrasound (LUS) even in the diagnostic regime can induce pulmonary capillary haemorrhage (PCH) at the alveolar epithelium-gas interface. Acoustic peak negative pressure in the range of 1.0–1.5 MPa correlates well with PCH threshold. However, in retrospective human studies, adverse events could not be demonstrated following LUS examination, which is evidence of symptomatic PCH after therapeutic ultrasound ablation in proximity of lung exists. Therefore, this subject remains controversial. This work summarizes the underlying physical causes and consequences of ultrasound induced PCH. The complexity of PCH thresholds depending on imaging modes, pathological lung conditions including ventilation parameters will be presented. In addition, current recommendations for the safe use of LUS based on Safety Indices given by AIUM and EFSUMB guidelines and the impact of LUS specific settings, available on modern scanners, will be discussed.