Recruitment maneuvers in three experimental models of acute lung injury - Effect on lung volume and gas exchange

Recruitment maneuvers (RM), consisting of sustained inflations at high airw ay pressures, have been advocated as an adjunct to mechanical ventilation i n acute respiratory distress syndrome (ARDS). We studied the effect of base line ventilatory strategy and RM on end-expiratory lung volume (EELV) and o xygenation in 18 dogs, using three models of acute lung injury (ALI; n = 6 in each group): saline lavage (LAV), oleic acid injury (OAI), and intratrac heal instillation of Escherichia coli (pneumonia; PNM). All three models ex hibited similar degrees of lung injury. The PNM model was less responsive t o positive end-expiratory pressure (PEEP) than was the LAV or OAI model. On ly the LAV model showed an oxygenation response to increasing tidal volume (VT). After RM, there were transient increases in Pao, and EELV when ventil ating with PEEP = 10 cm H2O. At PEEP = 20 cm H2O the lungs were probably fu lly recruited, since the plateau airway pressures were relatively high (app roximate to 45 cm H2O) and the oxygenation was similar to preinjury values, thus making the system unresponsive to RM. Sustained improvement in oxygen ation after RM was seen in the LAV model when ventilating with PEEP = 10 cm H2O and VT = 15 ml/kg. Changes in EELV correlated with changes in Pa-O2 on ly in the OAI model with PEEP = 10 cm H2O. We conclude that responses to PE EP, VT, and RM differ among these models of ALI. RM may have a role in some patients with ARDS who are ventilated with low PEEP and low VT.