Respiratory controversies in the critical care setting. Do the NIH ARDS Clinical Trials Network PEEP/FIO2 tables provide the best evidence-based guide to balancing PEEP and FIO2 settings in adults?

Positive end-expiratory pressure (PEEP) and inspired oxygen fraction (F(IO(2))) are the primary means of improving P(aO(2)) during mechanical ventilation. Patients with acute respiratory distress syndrome (ARDS) typically present with a large intrapulmonary shunt, which makes even high F(IO(2)) ineffective in improving P(aO(2)). PEEP decreases intrapulmonary shunt by recruiting collapsed alveoli, but PEEP is associated with important adverse effects, whereas prolonged exposure to high F(IO(2)) may cause oxidative lung injury. The improved survival found in the National Institutes of Health's ARDS Network low-tidal-volume study may suggest that their PEEP/F(IO(2)) titration tables represent the best method for adjusting these variables. Based upon an extensive literature review of PEEP and respiratory system mechanics in ARDS, we conclude that: (1) for most patients the therapeutic range of PEEP is relatively narrow, so the ARDS Network PEEP/F(IO(2)) strategy is reasonable and supported by high-level evidence, (2) how best to adjust PEEP to prevent or ameliorate ventilator-associated lung injury is unknown and still under investigation, and (3) in a small subset of patients with severe lung injury and/or abnormal chest-wall compliance, highly individualized titration of PEEP, based upon the respiratory-system pressure-volume curve, PEEP/tidal-volume titration grids, or a recruitment maneuver and a PEEP decrement trial is a reasonable alternative.