ARDSNet lower tidal volume ventilatory strategy may generate intrinsic positive end-expiratory pressure in patients with acute respiratory distress syndrome.

The ARDSNet trial revealed that the use of a smaller tidal volume (V-T) reduced mortality by 22%. However, three earlier studies that lowered V-T did not find a decrease in mortality. We tested the hypothesis that the increased respiratory rate used in the ARDSNet lower V-T strategy might have led to intrinsic positive end-expiratory pressure (PEEPi), raising total PEEP (PEEPtotal). Ten patients with acute respiratory distress syndrome (ARDS) were ventilated using the ARDSNet lower V-T protocol. Respiratory rate was then reduced (10-15 breaths/minute) to obtain a V-T of 12 ml/kg (ARDSNet traditional V-T). PEEP on the ventilator (PEEPnominal: 10.1 +/- 0.7 cm H2O), FIO2 (0.7 +/- 0.1), and minute ventilation (V-E: 12.4 +/- 1.7 L/minute) were set using the ARDSNet protocol and maintained constant during the two ventilatory strategies. Values of airway pressure at end-expiration of a regular breath (PEEPexternal) and 3-5 seconds after the onset of an end-expiratory occlusion (PEEPtotal) were measured. PEEPi was calculated by subtracting PEEPexternal from PEEPtotal. PEEPtotal and PEEPi were, respectively, 16.3 +/- 2.9 and 5.8 +/- 3.0 cm H2O during the lower V-T strategy and 11.7 +/- 0.9 and 1.4 +/- 1.0 cm H2O during the traditional V-T strategy (p < 0.01). The reduced mortality observed with the ARDSNet strategy may have been due to the protective effect of a higher PEEPtotal.