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

Abstract

Allen, Gilman, Lennart K. A. Lundblad, Polly Parsons, and Jason H. T. Bates. Transient mechanical benefits of a deep inflation in the injured mouse lung. J Appl Physiol 93: 1709-1715. First published July 12, 2002 10.1152/japplphysiol.00473.2002The lasting effects of a recruitment maneuver (RM) in the injured lung are not well characterized. We speculated that the reduction in respiratory elastance (H) after a deep inflation (DI) is transient in nature and should be sustained longer at higher positive end-expiratory pressure (PEEP). Thirteen ventilated mice were given 2 DIs at various levels of PEEP before and after saline lavage. Forced oscillations were used to measure H periodically over 7 min after the DIs. Time constants ( ) were estimated for the post-DI recovery in H. Values for before lavage (80-115 s) were reduced after lavage (13-30 s) at all levels of PEEP (P ϭ 0.0001). PEEP did not significantly influence before or after lavage. The plateau level and total recovery in H after a DI were significantly influenced by PEEP and lavage (P Ͻ 0.0001). Our results suggest that for a DI to be beneficial in the injured mouse lung, it may have to be applied several times a minute. atelectasis; acute lung injury; recruitment; elastance; positive-pressure respiration PHYSICIANS HAVE KNOWN for a long time that atelectasis plays a pivotal role in the development of hypoxemia during mechanical ventilation, both in general anesthesia for routine surgery and in various instances of acute lung injury. Recent practice has now moved toward the use of lower tidal volumes (VT) in patients with acute lung injury and acute respiratory distress syndrome (ARDS) after two important studies demonstrated lower mortality outcomes by using this strategy (1, 1a). However, because of the progressive alveolar derecruitment that is often encountered with the use of lower VT (27), there has been a renewed interest in the use of recruitment maneuvers (RMs) as a means of reopening these regions of atelectasis. Many studies have demonstrated improvement in oxygenation, respiratory system compliance, and even lung volume after sustained or deep inflations (DIs) in many different scenarios (3-5, 17, 18, 26, 28), but some of these same studies were unable to show any lasting improvement when RMs were delivered during conventional positive pressure ventilation (4,18,25).These apparently conflicting results may be explained by the different experimental situations involved, as the effect of a RM is likely to depend on the size and duration of the inflation, the mode of ventilation in which the inflation is delivered, and the level of positive end-expiratory pressure (PEEP) employed. 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 ...

Lung volume recruitment maneuvers and respiratory system mechanics in mechanically ventilated mice

“…Infrequent application of large RMs had transient effects on H; however the pattern of progressive increase in H after the IM followed a similar trajectory to that seen before the IM. This finding is in line with those from other studies in animals with healthy and pre-injured lungs (Mead and Collier, 1959;Allen et al, 2002;Allen et al, 2004;Frank et al, 2005;Allen et al, 2006;Ko et al, 2008) and may reflect inadequate PEEP during low V T ventilation.…”

“…It is essential to provide information on ventilator settings in order to facilitate future studies. However, apart from specific "recruitment maneuver studies" (Allen et al, 2002;Allen et al, 2004;Frank et al, 2005;Koh et al, 2005;Farias et al, 2005;Allen et al, 2006;Allen et al, 2007;Ko et al, 2008;Jonasson et al, 2008) few experimental studies using mechanical ventilation protocols provide detailed information on application, frequency, and type of lung volume recruitment maneuvers (RMs). Given that the mechanical properties of the respiratory system are specific to the lung volume at which their measurements are made (Sly et al, 2003) and to the lung volume history , it is surprising that details of RMs are not always reported.…”

Suppressive oligonucleotides inhibit inflammation in a murine model of mechanical ventilator induced lung injury

“…Tissue elastance began to rise after 1 h and reached significantly elevated levels at 2-4 h of MV (P<0.05, Figure 2). These changes were accompanied by a decrease in static compliance over the same period of time ( Figure 2) and were consistent with the effects of MV observed in other studies utilizing low ventilation volumes (29,30). By comparison, central airway resistance and lung tissue damping did not change over time.…”

Modeling the Complex Dynamics of Derecruitment in the Lung

“…15,26 Part of the confusion surrounding the use of recruitment maneuvers in ALI may stem from the underappreciated fact that recruitment and derecruitment in the lung are dynamic processes that evolve with time, 10 even in the face of a perfectly constant ventilatory regimen. Furthermore, several studies in mice from our laboratory [3][4][5][6] have shown that the dynamics of recruitment and derecruitment depend markedly on the nature and severity of lung injury, likely reflecting variations in the degree of instability of the liquid layer that lines the small airways.…”