Acute respiratory distress syndrome (ARDS) is one of the major causes of respiratory failure and hospital morbidity that nurses face today. It is significant that improvements in mortality and morbidity have not been achieved until recently. This is primarily due to an increased understanding in the pathophysiology of ARDS and the effects of our medical interventions.

The goal of this article is to explore the concept of acute lung injury, and to answer some of the questions nurses frequently have about ARDS.

What is ARDS?

Acute respiratory distress syndrome is a malignant inflammation of the lung in response to an identifiable injury or infection.

The term "malignant" probably brings to mind visions of terminal cancer. In the context of ARDS, the meaning is similar. Malignant cancer is the type that is out-of-control, and the body is unable to contain it. Similar variations occur in the inflammatory response with ARDS.

Normally inflammation is well controlled in the body. However, in ARDS inflammation exceeds the normal control mechanisms and begins to damage healthy tissue. Therefore, additional damage occurs before tissue repair begins.

The results of malignant inflammation of the lung can be classified into four major events:

The first event in inflammation is vasodilation. Initially, the increased perfusion from vasodilation will maintain the patient's oxygenation. Secondly, capillary permeability occurs to allow white blood cells and proteins to migrate to the area of injury. Leaking of fluid, WBCs, and proteins into the lung tissue causes pulmonary edema to form and is responsible for the "white out" seen on chest x-ray. Next, the clotting cascade is activated. This will result in microclotting occurring throughout the lung, causing millions of microscopic pulmonary emboli. As a result of these changes, the patient will develop hypoxemia. The lung's response to hypoxemia is vasoconstriction, which worsens oxygen perfusion.

How do we diagnose it?

The current diagnostic criteria are broad and not specific to the early detection of ARDS. They include:

If your patient presents with one or more of the above risk factors and progressive respiratory decompensation, suspect ARDS.

How can ARDS best be managed?

The best management strategies for ARDS include a balance of ventilatory assistance, hemodynamic support, nutrition, and management of the underlying risk factor.

Mechanical ventilation is often necessary for the treatment of ARDS. However, it must be managed carefully. Most recent research supports the use of low tidal volumes (5-6 mL/kg), moderate respiratory rates (20-28), and moderate levels of PEEP (8-12 cm/H2O). Care must be taken to use the lowest possible FiO2 to avoid further injury to the lung by oxygen toxicity. Alternate methods of delivery of ventilatory assistance should also be considered. These include:

Other interventions that may improve oxygenation include:

Hemodynamic support is often necessary as well. Care must be taken when resuscitating the patient with ARDS. Excessive fluid resuscitation can contribute to pulmonary edema formation. Vasopressors constrict pulmonary vessels and worsen hypoxemia.

ARDS causes increases in metabolism and oxygen consumption. Therefore, it is important to maintain nutrition by tube feedings or TPN. Your hospital dietitian should be able to assist in choosing the appropriate diet.

The malignant inflammation in ARDS is caused by one or more of the above risk factors. The most important treatment modality is to treat the underlying condition to "turn off" the stimulus of inflammation.

What's new in the treatment of ARDS?

The most significant strides made in the treatment of ARDS involve recognizing the deleterious effects of mechanical ventilation. All patients are different in how well they will tolerate mechanical ventilation, but the best practice to date recommends using low tidal volumes, low FiO2, with moderate respiratory rates, and moderate PEEP.

Inflammatory modulation may also be helpful. Corticosteroids given between day 5 and day 7 of ARDS have been shown to reduce secondary inflammation. Other inflammatory modulators that may be beneficial include:

Acute respiratory distress syndrome is a malignant inflammatory response of the lung that can be best managed by early detection, and aggressive management using moderate levels of mechanical ventilation, budgeting fluid resuscitation, and aggressively balancing oxygen supply and demand.