Repeated generation of the pulmonary pressure-volume curve may lead to derecruitment in experimental lung injury

Objective: Measurements from the pulmonary pressure-volume (PV) curve have been proposed to adjust ventilator settings. We investigated the effects of repeated construction of an inflation PV curve implemented in a standard ventilator on recruitment or derecruitment in acutely injured lungs. Design and setting: Prospective experimental animal study in eight anesthetized and mechanically ventilated pigs. Interventions: Acute lung injury was induced by lung lavage and animals were ventilated in volume controlled mode with PEEP 10 cmH₂O. The PV curve was constructed five times repeatedly by constant pressure rise, after which ventilation with the preset PEEP was resumed immediately. Studies of hemodynamics, lung mechanics, blood gases and computed tomography were carried out before and after maneuvers. Measurements and results: Derecruitment was assessed as an increase in nonaerated lung volume (V_NON), and V_PEEP was the end-expiratory volume difference between PEEP and ZEEP. There was a significant decrease in PaO₂ from 90.4±33.3 to 70.9±36.3 mmHg and a rise in venous admixture from 47.8±12.7 to 59.1±16.6%. V_PEEP was reduced from 244 to 202 ml. A corresponding decrease in normally aerated lung volume was observed, while regression analysis revealed increase in V_NON depending on the amount of preexisting atelectasis. Conclusions: Repeated generation of the PV curve with a readily available tool resulted in worsened oxygenation. Derecruitment of the lungs occurred with loss of PEEP at the start of the maneuver, which could not be recovered by a maximum inflation pressure of 40 cmH₂O. Repeated use of the investigated tool should be cautioned, and users should consider measures to preserve aerated lung volumes.