The RBC membrane becomes less deformable resulting in damage to the membrane when the RBC transits capillary beds. It was first reported over 20 years ago that the RBC cell membrane undergoes changes and is damaged as a result of sepsis, even in the absence of an associated hemolytic condition.
The purpose of this review is to examine the changes that occur to the RBC in critical illness, the contribution of the RBC to alveolar injury in ARDS, and potential interventions for future study. The red blood cell (RBC) also crosses the pulmonary capillary endothelium and can be found in the alveoli of patients with ARDS but until recently has primarily been viewed as a bystander to the alveolar inflammation and coagulation that occurs in ARDS. Given the known inflammation and coagulation that occur with ARDS, pharmacologic therapies have focused on these targets to try to improve clinical outcomes but with no benefit. The pulmonary capillary endothelium is also disrupted causing an influx of proteinacious fluid and white blood cells into the alveolus resulting in diffuse pulmonary inflammation and coagulation. In the case of direct injury to the lung epithelium by pneumonia, for example, there is an increase in epithelial permeability, and normal clearance of fluid from the alveolus is disrupted. Since the first description of ARDS in 1967, investigation into the pathophysiology of ARDS has focused on the interaction between the underlying cause, the lung endothelium, vasculature, and epithelium, and circulating white blood cells and platelets. The lack of targeted pharmacologic therapies may be a result of an incomplete understanding of the underlying pathophysiology of ARDS. Although processes of care interventions such as lung protective ventilation, prone positioning, and neuromuscular blockade may be beneficial, there are no specific pharmacologic interventions to improve outcomes in this patient population. This syndrome of acute lung inflammation and non-cardiogenic pulmonary edema is associated with significant morbidity and mortality during the acute hospitalization along with poor long-term outcomes including reduced functional status and increased mortality even beyond the initial hospitalization. The acute respiratory distress syndrome (ARDS) frequently complicates critical illness from a variety of underlying causes.
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