Monitoring patients with ARDS, part 2: Pulmonary oxygen uptake: Looking beyond PaO₂ for assessment and management

An essential goal in the treatment of the acute respiratory distress syndrome is the maintenance of adequate oxygenation, but deciding on the most appropriate therapeutic option depends on clinical judgment as to whether intrapulmonary shunting or a combination of shunting and ventilation-perfusion disturbance or mismatch is responsible for impaired pulmonary gas exchange and resultant hypoxemia. Because the physical findings of hypoxemia are nonspecific, the clinician may not be able to adequately assess the severity of oxygen depletion without measuring PaO₂. However, the changes in lung function that cause hypoxemia cannot be inferred from measurements of PaO₂. Therefore, several oxygenation indices have been developed to guide the assessment of the cause of hypoxemia and the selection of a management strategy.