Recruitment Maneuvers in Three Experimental Models of Acute Lung Injury

Abstract

Recruitment maneuvers (RM), consisting of sustained inflations at high airway pressures, have been advocated as an adjunct to mechanical ventilation in acute respiratory distress syndrome (ARDS). We studied the effect of baseline ventilatory strategy and RM on end-expiratory lung volume (EELV) and oxygenation in 18 dogs, using three models of acute lung injury (ALI; n = 6 in each group): saline lavage (LAV), oleic acid injury (OAI), and intratracheal instillation of Escherichia coli (pneumonia; PNM). All three models exhibited similar degrees of lung injury. The PNM model was less responsive to positive end-expiratory pressure (PEEP) than was the LAV or OAI model. Only the LAV model showed an oxygenation response to increasing tidal volume (VT). After RM, there were transient increases in Pa(O(2)) and EELV when ventilating with PEEP = 10 cm H(2)O. At PEEP = 20 cm H(2)O the lungs were probably fully recruited, since the plateau airway pressures were relatively high ( approximately 45 cm H(2)O) and the oxygenation was similar to preinjury values, thus making the system unresponsive to RM. Sustained improvement in oxygenation after RM was seen in the LAV model when ventilating with PEEP = 10 cm H(2)O and VT = 15 ml/kg. Changes in EELV correlated with changes in Pa(O(2)) only in the OAI model with PEEP = 10 cm H(2)O. We conclude that responses to PEEP, 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.

Transient mechanical benefits of a deep inflation in the injured mouse lung

“…The role of the RM is then to reach the higher critical opening pressures for segments not opened during normal tidal inflations (6,23). This means that the amount of recruitable lung decreases with increasing PEEP (5,17,27). This was clearly the case in the present study after lung injury because we found that increasing PEEP markedly reduced baseline H (Fig.…”

“…Indeed, studies have demonstrated reductions in lung compliance and increased lung volumes after RMs delivered during high-frequency ventilation (3,4,18) but not during conventional positive pressure ventilation (4,18). In addition, sustained DIs have been shown to result in greater recruited lung volumes when using low VT or low levels of PEEP but not with high VT or high PEEP (17). Nevertheless, despite using conventional positive pressure ventilation with a moderate VT in our study, we were still able to demonstrate an improvement in H after a DI both at baseline and after lavage.…”

“…Furthermore, if the effects of a RM are transient, then its apparent benefits will depend on when they are measured. Different researchers have measured the effects of a RM at different time points after its administration (3,4,17,26,28), yet there has been little attempt to characterize the rate at which the benefits of a RM are lost in the period immediately after its delivery.The goal of our study, therefore, was to characterize the effects of a DI on lung mechanics during conventional mechanical ventilation in a mouse model of lung injury. We followed a measure of respiratory elastance (H) as an index of ongoing derecruitment after DI, both at baseline and after saline lavage at various levels of PEEP.…”

“…Furthermore, if the effects of a RM are transient, then its apparent benefits will depend on when they are measured. Different researchers have measured the effects of a RM at different time points after its administration (3,4,17,26,28), yet there has been little attempt to characterize the rate at which the benefits of a RM are lost in the period immediately after its delivery.…”

Variable positive end-expiratory pressure can maintain oxygenation in experimental acute respiratory distress syndrome induced by oleic acid in dogs

“…Thus, further collapsed areas were opened before we started the variation. The application of the recruitment maneuver (23,24) has been standardized by Lachmann (19) according to "the open-lung concept". There is no doubt that initial lung recruitment rapidly improves oxygenation, which will only be maintained when using high PEEP levels (25)(26)(27)(28)(29).…”