A RM consisting in interleaving uninterrupted mechanical ventilation with a certain number of breaths with a higher plateau pressure is referred to as ‘sigh’ RM and was the first technique proposed [24]. Such maneuver has been showed to improve oxygenation, lung compliance, and increase EELV, but these benefits are transient, and the sigh has to be performed frequently in order to maintain the patency of recruited lung units [27]. In animal models, patterns of sigh RMs with high frequency, e.g., 180/h as proposed in the first studies, were associated with elevated inflammation markers compared to ventilation without RMs and to CPAP maneuvers [28]. However, the clinical relevance of these aspects remains to be clarified. With the increased availability of more sophisticated ICU ventilators, sighs can be delivered with a predetermined frequency. Due to the lack of evidence concerning their safety and long-term efficacy, their routine cannot be recommended.

Sustained Inflation

Sustained inflation is the most described RM. It is performed increasing abruptly the airway pressure to a certain level and maintaining it constant for several seconds. A common sustained inflation maneuver consists in the application of a constant airway pressure of 40 cmH2O for 40s [29, 30]. These RMs can rapidly revert

Types of recruitment maneuvers

Fig. 5.1 Types of recruitment maneuvers. Sigh maneuver (a), typical sustained inflation maneuver (b), slow stepwise maneuver based on step-by-step changes in PEEP (c) atelectasis and cause an improvement of oxygenation and lung function in the short term in clinical and experimental settings; however their role in achieving a prolonged gas exchange amelioration is less clear [20, 31, 32]. However, in a study comparing sustained inflation with other RMs, a more persistent effect was observed [33]. Since the pressure rise mediates both the effectiveness RM and VILI, caution is recommended in translating into clinical practice the results of small sampled observational studies, in which long-term safety is difficult to assess.

Slow Stepwise Maneuvers

Efforts were made by the researchers to find alternatives to the sustained inflation RM, possibly achieving a comparable efficacy with less risks in terms of hemodynamic impairment and barotrauma. Slow increases of plateau pressure, performed with stepwise adjustments of airway pressure and/or PEEP, were proposed with this aim in ICU patients [7] and during general anesthesia for surgery [34, 35]. Stepwise maneuvers could allow a better control of airway pressure increase compared to sustained inflation, resulting in a decreased risk for hyperinflation and hypotension. In several experimental studies, stepwise RMs resulted in a more prolonged benefit than conventional RMs [36], were associated with lower inflammatory markers [26], and reduced epithelial cell damage in mild ARDS [37]. Despite this, large trials are warranted to assess the safety and efficacy of RMs and advantages of specific techniques [38].

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