Atelectosis (from ancient Greek ἄτηλκος - “underdeveloped” + Greek έκατος - “cup”) is the presence in the lung tissue of a part of the former alveolar area with a relatively small volume of residual structural elements of the lung tissue and almost complete loss of elastic tissue [1]. In the tissue structure, atelectosis gradually disappears due to the processes of sclerosis and lysis. Atelectosis can be primary or secondary [2]. It is observed with adynamic ventilation, pathological (for example, interstitial) fibrosis due to the inflammatory process and pulmonary infarctions [3]. Atelectosis cannot be considered a normal condition; it occurs during pathological processes in the lungs caused by various factors. Unlike other respiratory diseases, atelectosis is not based on a purulent-inflammatory or infectious process, but on chronic, toxic, thermal or mechanical damage to the lungs. Atelectic pneumonia is common.