Positive End-Expiratory Pressure after a Recruitment Maneuver Prevents Both Alveolar Collapse and Recruitment/Derecruitment

TLDR

The study tested whether alveoli opened by a recruitment maneuver remain stable without sufficient PEEP. In anesthetized pigs with surfactant deactivation, a recruitment maneuver (45 cm H₂O, 35 cm H₂O PEEP for 1 min) was performed and alveolar number and stability were quantified using an in‑vivo microscope, then animals were randomized to 5 cm H₂O or 10 cm H₂O PEEP for further assessment. The recruitment maneuver opened many alveoli that were stable during the maneuver, and while both 5 cm H₂O and 10 cm H₂O PEEP improved oxygenation, only the 10 cm H₂O group maintained alveolar stability, indicating that inadequate PEEP after recruitment can lead to unstable alveoli and potential ventilator‑induced lung injury.

Abstract

We tested the hypothesis that collapsed alveoli opened by a recruitment maneuver would be unstable or recollapse without adequate positive end-expiratory pressure (PEEP) after recruitment. Surfactant deactivation was induced in pigs by Tween instillation. An in vivo microscope was placed on a lung area with significant atelectasis and the following parameters measured: (1) the number of alveoli per field and (2) alveolar stability (i.e., the change in alveolar size from peak inspiration to end expiration). We previously demonstrated that unstable alveoli cause lung injury. A recruitment maneuver (peak pressure = 45 cm H2O, PEEP = 35 cm H2O for 1 minute) was applied and alveolar number and stability were measured. Pigs were then separated into two groups with standard ventilation plus (1) 5 PEEP or (2) 10 PEEP and alveolar number and stability were again measured. The recruitment maneuver opened a significant number of alveoli, which were stable during the recruitment maneuver. Although both 5 PEEP and 10 PEEP after recruitment demonstrated improved oxygenation, alveoli ventilated with 10 PEEP were stable, whereas alveoli ventilated with 5 PEEP showed significant instability. This suggests recruitment followed by inadequate PEEP permits unstable alveoli and may result in ventilator-induced lung injury despite improved oxygenation.