Acute respiratory distress syndrome (ARDS) is a distinct type of hypoxemia that was first called “shock lung” by the military in the 1960’s. Healthy lungs require dry alveoli and a small amount of interstitial fluid to work properly. ARDs disrupts the regulation and movement of fluids via increased alveolar capillary membrane permeability, resulting in excess fluid in both the interstitium and alveoli, leading to impaired gas exchange, decreased lung compliance, and increased pulmonary arterial pressure. ARDS is commonly associated with sepsis however, there are several non-infectious treatment that may also result in ARDS including massive blood transfusions of > 15 units of packed red blood cells and as little as one unit of plasma, lung transplantation related to primary graft failure, hematopoietic stem cell transplantation due to infectious and non-infectious causes, chemoradiation due to lung injury, thoracic surgery cardiopulmonary bypass, and drug toxicity due to the administration of amiodarone or other medications (Siegel, 2022).
Assessment findings in a patient with ARDS may include dyspnea, decreased arterial oxygen saturations, tachypnea, tachycardia, diffuse crackles, severe acute confusion cyanosis, and diaphoresis. Chest radiographs can be normal within 24 hours of initial lung insult and then may show diffuse bilateral opacities with dependent atelectasis that cannot be fully explained by pleural effusions, lobar collapse, lung collapse, and or pulmonary nodules. CT of the thorax may reveal widespread patchy or coalescent airspace opacities more apparent in dependent lung area and can resemble “ground glass” (Siegel, 2022).
Most patients with ARDS will require mechanical ventilation, which although beneficial in enhancing gas exchange and decreasing the work of breathing, is also associated with lungs damage due to positive pressures. Ventilator associated lung injury (VALI) is a molecular response to the application of abnormal forces within the lung resulting in inflammation, edema, and extracellular matrix remodeling, which can spread to cause multiple system organ dysfunction (MODS). There are three types of VALI including biotrauma, barotrauma, and atelectrauma. Biotrauma results from the use of positive pressure, which triggers the release of proinflammatory cytokines and neutrophilic infiltrates with systemic dissemination, leading to MODS. Barotrauma is associated with high ventilator pressures and subsequent alveolar over-stretching and edema. Atelectrauma is the result of epithelial damage by shear forces between air and fluid, leading to “open collapse phenomenon.” The latter of the VALI is minimized by peep (Rodriguez et al, 2017).
References
Rodriguez, A.L., del Busto, C., Garcia-Prieto, E., & Albaiceta, G.M. (2017). Mechanical ventilation in acute respiratory distress
syndrome. Medicina Intensiva, 41(9), 550-558. https://doi:10.1016/j.medine.2016.12.005
Siegel, M.D. (2022). Acute respiratory distress syndrome: Clinical features, diagnosis, and complications in adults. Retrieved on May
19, 2022, from https://www.uptodate.com/contents/acute-respiratory-distress-syndrome-clinical-features-diagnosis-and-complications-
