Severe hypoxemia is still a major problem in the intensive care unit (ICU). Here, we will limit our discussion to the hypoxemia due to acute lung injury (ALI), of which the acute respiratory distress syndrome (ARDS) represents an extreme case, and we will describe the therapeutic approach in the early phase of ALI/ARDS. ALI and
ARDS have recently been defined by the American-European Consensus Conference on ARDS (Bernard. etal 1994). Both are characterized by bilateral pulmonary infiltration, edema, and low compliance of the respiratory system. They are distinguished by blood gas values: ALI is defined by a PaO^FiO2 ratio below 300 mmHg (40 kPa), and ARDS by a PaO^FiO2 ratio below 200 mmHg (26.7 kPa), where PaO2 is the arterial oxygen tension and FiO2 is the fractional inspired oxygen, irrespective of the level of positive end-expiratory pressure (PEEP) in use. However, this distinction is arbitrary, and the selected thresholds are not related to outcome.
We describe the approach to the individual patient, which is not substantially different in ALI and ARDS. The rational approach must include the following:
1. understanding the etiology and pathogenesis;
2. understanding the underlying pathology;
3. tailoring the symptomatic respiratory treatment to the individual patient;
4. general rules for setting mechanical ventilation.
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