Bench-to-bedside review: Recruitment and recruiting maneuvers

Abstract

In patients with acute respiratory distress syndrome (ARDS), the lung comprises areas of aeration and areas of alveolar collapse, the latter producing intrapulmonary shunt and hypoxemia. The currently suggested strategy of ventilation with low lung volumes can aggravate lung collapse and potentially produce lung injury through shear stress at the interface between aerated and collapsed lung, and as a result of repetitive opening and closing of alveoli. An 'open lung strategy' focused on alveolar patency has therefore been recommended. While positive end-expiratory pressure prevents alveolar collapse, recruitment maneuvers can be used to achieve alveolar recruitment. Various recruitment maneuvers exist, including sustained inflation to high pressures, intermittent sighs, and stepwise increases in positive end-expiratory pressure or peak inspiratory pressure. In animal studies, recruitment maneuvers clearly reverse the derecruitment associated with low tidal volume ventilation, improve gas exchange, and reduce lung injury. Data regarding the use of recruitment maneuvers in patients with ARDS show mixed results, with increased efficacy in those with short duration of ARDS, good compliance of the chest wall, and in extrapulmonary ARDS. In this review we discuss the pathophysiologic basis for the use of recruitment maneuvers and recent evidence, as well as the practical application of the technique.

Figure 1

Schematic representation of mechanisms of injury during tidal ventilation. Dependent areas are poorly aerated at end-expiration because of compressing hydrostatic pressures. At end-inspiration, patent alveoli may become over-stretched (A), excessive stresses may be generated at the boundary between aerated and nonaerated lung tissue (B), and dependent alveoli may be repetitively opened and closed producing tissue damage (C).

Figure 2

Pressure–volume curve demonstrating tidal ventilation at various positive end-expiratory pressure levels. Tidal ventilation is shown at 12, 18 and 24 cmH₂O with no recruitment effect (solid lines); at 18 cmH₂O with partial recruitment (18a), and at 12 and 24 cmH₂O following an effective recruitment manuever (12a, 24a).