An alternative approach is to perform periodically large sustained lung inflations. In this connection, it should be noted that in spontaneously breathing postoperative patients, periodic deep breaths, in the form of incentive spirometry, are an effective and common modality for treating atelectasis. (4) In our patients, application of PEEP produced an increase in EELV and Cst,rs, at ZEEP, which probably reflects a persistent reopening of atelectatic lung units. This finding is consistent with the observations of Mead and Collier and Bendixen et al, who found that lung compliance increased immediately after forced inflation of the lungs, and attributed it to recruitment of previously closed lung units.

Based on that study, the use of periodic inflations with large tidal volume (sighs) was adopted during mechanical ventilation. Recently, however, with the administration of large tidal volumes (10 to 15 ml/kg) and PEEP, the use of sighs has been generally abandoned. Our study suggests that even when relatively large tidal volumes are used (in the order of 12 ml/kg in our patients) in association with low levels of PEEP, large periodic inflations (sighs) might be beneficial in reopening atelectatic units. This, however, needs to be confirmed in further clinical investigations.