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Physiology of Recruitment Maneuvers

Definition and Rationale

The transpulmonary pressure, calculated as difference between airway pressure and pleural pressure, is the mediator of lung recruitment and represents the distending force of the lung. A RM is a transient increase of the transpulmonary pressure, sufficient to overcome the chest wall elastance and to open collapsed alveoli [11]. In ARDS, the loss of aeration is due to alveolar flooding, as well as resorption and compression atelectasis. In most of the cases, moderate-high airway pressures, between 30 and 40 cmH2O, are able to recruit most of the compression atelectasis, while loss of aeration due to resorption mechanisms may require higher pressures, especially when a rigid chest wall coexists, such as in obese patients [12]. The potential of lung recruitment can be defined as the increase in end-expiratory lung volume or as a decrease in the non-aerated lung regions as a consequence of an increase of the transpulmonary pressure and has huge heterogeneity in ARDS patients [13]. Most of the studies investigated the use of RMs in patients with injured lungs; however they might have a role also in patients with healthy lungs both in the ICU and in the operating room, and their efficacy in those settings is under investigation [14-16]. Moreover, it must be underlined that even if the transpulmonary pressure is the real mediator of RMs, in most of the patients, its actual value is not known, because pleural pressure estimation with esophageal pressure monitoring is not often implemented in the clinical practice. Therefore in most cases the clinician sets the airway pressure on the ventilator rather than the transpulmonary pressure.

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