ARDS is the name given to the clinical manifestation of a number of indirect lung injury states characterized by dyspnea, severe hypoxemia, and decreased lung compliance with radiographic evidence of diffuse bilateral pulmonary infiltrates. Alveolar consolidation with fluid, protein, and inflammatory cells in the presence of a normal capillary or wedge pressure is also a characteristic finding, i.e., low pressure pulmonary edema. The altered permeability results in a rapid movement of fluid from plasma to interstitial space with even a normal capillary (wedge) pressure. The causes and differential diagnosis of ARDS are presented.

The lung damage is the result of a systemic process initiated by burn tissue, infection or inflammation rather than a direct lung injury. However, the term "ARDS" is commonly but inappropriately used to describe direct lung injury processes, such as an inhalation injury. There are probably several distinct ARDS state, each with a different cause. Although the pathophysiology may be extremely complex and the etiologic agents varied, the presenting signs and symptoms for the ARDS states are nearly identical. The hypoxemia produced is characteristically refractory to an increase in fractional inspired oxygen, indicating increased shunting. In addition, the degree of shunt is not directly correlated with the degree of increased water content, as is the case with cardiogenic edema.

There is definitely a significant ventilatory impairment or airways component to the disease process not related to water. There is a decrease in dynamic compliance and functional residual capacity resulting in increased ventilation to perfusion mismatch, probably due to mediator-induced broncho constriction.

• Initial Onset

Administer oxygen: maintain oxygen saturation more than 90%
Determine and delete source of lung response
Maintain perfusion but avoid volume overload

• Phase 2 (2-7 days post-onset)

Administer oxygen; maintain oxygen saturation more than 90%
May need positive airway pressure (PEEP, CPAP)
Avoid volume overload (consider pulmonary artery catheter)

• Phase 3 (10 days plus)

Requires positive pressure ventilation; add PEEP
Needs pulmonary artery catheter
Adjust PEEP, tidal volume to improve static compliance and arterial oxygen tension but not impair oxygen delivery
Maintain wedge pressure below 15mmHg, preferably 10 to 12 mmHg.
Maintain blood volume and hemoglobin

Once resuscitation is completed and the patient has become stabilized and is beginning to be more active, there is a tendency to be lulled into complacency regarding pulmonary support. The patient remains at high risk for pneumonia for several weeks.

Maintenance of a "normal" minute ventilation in the perioperative period is not adequate in a patient generating up to twice the normal amount of carbon dioxide. Hypercapnia in the intraoperative or early postoperative period with its resultant massive catecholamine release can almost always be avoided by maintaining preoperative ventilatory needs in the intra- and postoperative period.

A two- to threefold increase in minute ventilation is a substantial work load. Ventilatory assist may be needed and should be initiated before respiratory deterioration.

Although a tracheostomy is usually not indicated in the first several days and is contraindicated through burn tissue, its use for chronic respiratory support is very advantageous. A tracheostomy through a non-burn or excised and grafted skin can improve pulmonary toilet, improve rehabilitation efforts by physical therapy, and will improve comfort.

THIS CONCLUDES THE END OF PULMONARY PROBLEMS