Hemodynamic monitoring of ARDS by critical care echocardiography
Acute respiratory distress syndrome (ARDS) is a major cause of morbidity and mortality in intensive care units and affects about 10% of critically ill patients and almost 25% of mechanically ventilated patients. It is characterized by life-threatening impairment of pulmonary gas exchange, but in two-thirds of cases is associated with hemodynamic instability. Shock is the primary factor influencing mortality and is driven by sepsis in half of the cases and by a more specific mechanism of ARDS in the other half, which is pulmonary vascular dysfunction, i.e., pulmonary hypertension related to the inflammatory process in the lung, which is very sensitive to a respiratory strategy. ARDS-related right ventricular failure, which is also named acute cor pulmonale (ACP), occurs in 20–25% of patients in the area of lung protective ventilation. In this condition, critical care echocardiography (CCE) plays a central role in adequate hemodynamic assessment and management at the bedside because of its ability to yield information quickly on cardiac dimensions and function, respiratory variations of vena cava dimensions and changes in cardiac output in response to therapy. Added to clinical and laboratory data, with invasive blood pressure monitoring and a central venous catheter, such information can be used to define the cause of circulatory failure, to evaluate the benefit and risk balance of fluid expansion, and to consider a strategy for right ventricle protection. Moreover, in the most severe situations, CCE can also guide the establishment and good functioning of extracorporeal membrane oxygenation (ECMO). In this article, we illustrate and summarize the value of CCE in ARDS and give some physiological pointers to its appropriate use.