Lung recruitment maneuvers in acute respiratory distress syndrome and facilitating resolution

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Abstract
To summarize the possible ways that acute respiratory distress syndrome (ARDS) lungs can be recruited and to present the experimental and clinical results of these maneuvers, along with the possible effects on patient outcome. Selected published medical literature from 1972 to 2002 and personal observations. In the experimental setting, repeated derecruitments accentuate lung injury during mechanical ventilation, whereas open lung concept strategies can attenuate lung injury. In the clinical setting, recruitment maneuvers that use a continuous positive airway pressure of 40 cm H(2)O for 40 secs improve oxygenation in patients with early ARDS who do not have an impairment in the chest wall. High intermittent positive end-expiratory pressure (PEEP), intermittent sighs, or high-pressure controlled ventilation improves short-term oxygenation in ARDS patients. Both conventional and electrical impedance thoracic tomography studies indicate that high airway pressures increase the lung volume and recruitment percentage of lung tissue in ARDS patients. To sustain the recruited ARDS lungs, it is important to maintain adequate PEEP levels. High PEEP/low tidal volume ventilation was seen to reduce inflammatory mediators in both bronchoalveolar lavage and plasma, compared with low PEEP/high tidal volume ventilation, after 36 hrs of mechanical ventilation in ARDS patients. Recruitment maneuvers that used continuous positive airway pressure levels of 35-40 cm H(2)O for 40 secs, with PEEP set at 2 cm H(2)O above the Pflex (the lowest inflection point on the pressure-volume curve), and tidal volume <6 mL/kg were associated with a 28-day intensive care unit survival rate of 62%. This contrasted with a survival rate of only 29% with conventional ventilation (defined as the lowest PEEP for acceptable oxygenation without hemodynamic impairment with a tidal volume of 12 mL/kg), without recruitment maneuvers (number needed to treat = 3; p <.001). High airway pressures can open collapsed ARDS lungs and partially open edematous ARDS lungs. High PEEP levels and low tidal volume ventilation decrease bronchoalveolar and plasma inflammatory mediators and improve survival compared with low PEEP/high tidal volume ventilation. In the near future, thoracic computed tomography associated with high-performance monitoring of regional ventilation (electrical impedance tomography) may be used at the bedside to determine the optimal mechanical ventilation of ARDS patients.