in the previous issue of critical care , koefeld - nielsen and colleagues   provide us with interesting experimental data regarding the question of how to predict response to a recruitment manoeuvre before applying it . they conducted an animal study ( lavage - induced experimental lung injury ) to test the hypothesis that parameters derived from the pressure - volume ( pv ) loop recorded before application of the lung recruitment manoeuvre ( lrm ) predict the effects of the lrm on gas exchange , respiratory system compliance ( crs ) and changes in end - expiratory lung volume ( eelv ) . the parameter derived from the pv loop was the maximal volume difference between the inspiratory and the expiratory limbs of the pv loop at a given pressure , indicating the maximal hysteresis area . this was expressed as a ratio of the total lung capacity , measured as the volume gained on the pv loop at 4 kpa airway pressure . furthermore , they hypothesized that the volume difference between the inspiratory and expiratory limbs of the pv curve at a given pressure would correspond to the change in eelv after the lrm at the same pressure . both hypotheses were validated in their well controlled experimental study design . specifically , a maximal hysteresis / total lung capacity ratio of 0.3 predicted improvement in crs , eelv and gas exchange after the lrm . this easily applicable method provides a means to predict the potential for recruitment , which is of paramount importance to recruitment strategies in acute lung injury . however , we do not have any convincing evidence that recruitment strategies improve clinical outcomes of patients with acute lung injury ( ali)/acute respiratory distress syndrome ( ards ) [ 3 - 5 ] , although many physiological studies could demonstrate a recruitment - induced increase in crs , eelv and gas exchange ( see ) . recruitment of lung volume is critical in ali / ards , in which loss of aerated lung volume is an important pathophysiological factor that leads to intra - pulmonary shunting of blood , culminating in severe hypoxaemia . consequently , the effect of recruitment in the clinical setting is mostly assessed by determining the effect on gas exchange . however , computed tomography ( ct ) studies   indicate that dissociation between mechanical effects and the gas exchange effect of lrm can occur , rendering gas exchange a rather insensitive parameter with which to assess lrm . the reason for this dissociation is that gas exchange only improves when ventilation / perfusion ratios are affected concomitantly ; specifically , ventilation must improve and perfusion must not diminish . however , because lrm might also have effects on the perfusion site , gas exchange merely reflects the functional effect of recruitment , whereas lung mechanics or ct analysis might reflect anatomical changes brought about by the lrm . ct analysis may therefore be helpful in identifying the potential for recruitment as well as for assessing anatomical effects on lung ventilation . however , clinically , it is not practical to conduct repeated ct analyses in patients with severe ards patients in order to optimize the ventilator settings or guide a recruitment strategy . hence , the observation that routine , detailed analysis of a single pv loop might be helpful in predicting the anatomical effect of a lrm is of great interest . it is consistent with the finding that analysis of lung mechanics might be more accurate than gas exchange in assessing the effect of lrm , insofar as it emphasizes the effect on respiratory mechanical behaviour rather than functional results . it is important to appreciate this because many studies were required to teach us that achievement of optimal gas exchange is not necessarily associated with the best outcomes in patients . how could the information provided by koefeld - nielsen and colleagues   be used clinically ? their method could be used as a diagnostic tool to determine potential for recruitment in individual patients , who could then be stratified as possible responders or nonresponders in a clinical study of a recruitment strategy that applies only to responders . this makes perfect sense because it is reasonable to assume that any potential evidence in favour of a recruitment strategy in ali / ards , in terms of clinical outcomes , will only be found if responders are subjected to the manoeuvre . we would be able to enter into a strategy of testing ali / ards therapies tailored to individual pathophysiological observations , rather then just randomizing large groups of patients who share only a rather unspecific diagnosis , namely ali / ards as defined by gas exchange and radiographical criteria . i am absolutely convinced that this is the way to go for future studies in our field . before doing so , however , the experimental observation made by koefeld - nielsen and colleagues   must be assessed clinically . if the method presented proves to be sufficiently robust to reflect the effect of lrms before they are actually applied , then this could be the basis for a larger clinical trial , in which it is used as a diagnostic tool to stratify patients before randomization . i look forward to seeing this work followed ; i consider it the way to go . ali = acute lung injury ; ards = acute respiratory distress syndrome ; eelv = end - expiratory lung volume ; crs = respiratory system compliance ; ct = computed tomography ; lrm = lung recruitment manoeuvre ; pv = pressure - volume .
using recruitment manoeuvres in acute lung injury remains a controversial issue because no convincing outcome data support their general use , although many physiological studies have demonstrated beneficial effects on lung compliance , end - expiratory lung volume and gas exchange . 
 one of the reasons why physiologically meaningful observations do not translate into clear clinical benefit could be the heterogeneity of the studied patient population . in patients with consolidated lungs and 
 only limited potential for recruitment , manoeuvres might be harmful , whereas in patients with high potential for recruitment they might be helpful . 
 however , when those populations are mixed any signal may be lost because of counteracting effects , depending on how the patient population was mixed . 
 we do not currently have any simple tool that may readily be applied at the bedside to assess the recruitment potential in an individual patient , which would be a sine qua non for identifying a homogeneous population in a recruitment study . 
 therefore , the method presented by jacob koefeld - nielsen and colleagues in the previous issue of critical care provides us with a simple method that could be used at the bedside to assess recruitment potential before the manoeuvre is applied .