Influence of tidal volume on alveolar recruitment - Respective role of PEEP and a recruitment maneuver

Both reduction in tidal volume (VT) and alveolar recruitment may be importa nt to limit ventilator-associated lung injury during mechanical ventilation of patients with the acute respiratory distress syndrome (ARDS). The aim o f this study was to assess the risk of alveolar derecruitment associated wi th VT reduction from 10 to 6 ml/kg. Whether this VT-related derecruitment c ould be reversed, either by a recruitment maneuver or by an increase in pos itive end-expiratory pressure (PEEP) level, was also investigated. Fifteen patients with ARDS were successively ventilated using conventional VT (CVT = 10 +/- 1 ml/kg) and low VT (LVT = 6 +/- 1 ml/kg); total PEEP (PEEPtot) wa s individually set at the lower inflection point (Plip) of the pressure-vol ume curve (PEEPtot = 11 +/- 4 cm H2O). Pressure-volume curves were recorded from zero PEEP (ZEEP) and from PEEP, and recruited volume (Vrec) was calcu lated as the volume difference between the two curves for a given pressure. Despite a similar PEEPtot, Vrec was significantly lower with LVT than with CVT, indicating low VT-induced alveolar derecruitment. Reduction in VT was associated with a reduced Sa(O2). In 10 patients, Vrec was also measured b efore and after a recruitment maneuver (two sustained inflations at 45 cm H 2O), and after an increase in PEEP (by 4 cm H2O). Low VT-induced derecruitm ent was reversed by a recruitment maneuver and by increasing PEEP. We concl ude that a reduction in VT could be responsible for alveolar derecruitment, which may be transiently reversed by a reexpansion maneuver or prevented b y a PEEP increase above Flip.