![]() Eventually, all of the gas in that segment will be absorbed and, without return of ventilation, the airway will collapse. Perfusion to the area is maintained however, so gas uptake into the blood continues. The obstruction either partially or completely inhibits ventilation to the area. Obstructive atelectasis is often referred to as resorptive atelectasis and occurs when alveolar air gets absorbed distal to an obstructive lesion. This is typically seen in bronchioalveolar carcinoma and results in complete lung collapse. Replacement atelectasis is one of the most severe forms and occurs when all of the alveoli in an entire lobe are replaced by tumor. Relaxation atelectasis involves the loss of contact between parietal and visceral tissue as seen in pneumothoraces and pleural effusions. Processes that lead to cicatrization atelectasis include tuberculosis, fibrosis, and other chronic destructive lung processes. Cicatrization atelectasis is often the result of parenchymal scarring of the lung, leading to contraction of the lung. ![]() Surfactant functions to decrease alveolar surface tension and prevent alveolar collapse therefore, any alterations to surfactant production and function often manifest as an increase in the surface tension of the alveoli leading to instability and collapse. Patients lying supine have cephalad displacement of the diaphragm further decreasing the transmural pressure gradient and increasing the likelihood of atelectasis. Adhesive atelectasis is often the result of a surfactant deficiency or dysfunction as seen in ARDS or RDS in premature neonates. This process is inhibited by general anesthesia due to diaphragm relaxation. The decrease in pressure allows for passive movement of air into the lungs. In an awake, spontaneously-ventilating patient, caudad excursion of the diaphragm during contraction causes a subsequent decrease in intrapleural pressure and alveolar pressure. In other words, there is a decreased transmural pressure gradient (transmural pressure gradient = alveolar pressure - intrapleural pressure) across the alveolus resulting in alveolar collapse. Compression atelectasis is secondary to increased pressure exerted on the lung causing the alveoli to collapse. Nonobstructive atelectasis can further classify into compression, adhesive, cicatrization, relaxation, and replacement atelectasis. ![]() Ītelectasis can categorize into obstructive, non-obstructive, postoperative, and rounded atelectasis. The mechanism by which atelectasis occurs is due to one of three processes: compression of lung tissue (compressive atelectasis), absorption of alveolar air (resorptive atelectasis), or impaired pulmonary surfactant production or function.
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