Influence of lung collapse distribution on the physiologic response to recruitment maneuvers during noninvasive continuous positive airway pressure

Purpose: Noninvasive continuous positive airway pressure (n-CPAP) has been proposed for the treatment of hypoxemic acute respiratory failure (h-ARF). Recruitment maneuvers were shown to improve oxygenation, i.e., the ratio of arterial oxygen tension to inspiratory oxygen fraction (PaO 2/FiO 2), during either invasive mechanical ventilation, and n-CPAP, with a response depending on the distribution of lung collapse. We hypothesized that, during n-CPAP, early h-ARF patients with bilateral (B L) distribution of lung involvement would benefit from recruitment maneuvers more than those with unilateral (U L) involvement. Methods: To perform a recruitment maneuver, once a minute we increased the pressure applied to the airway from 10 cmH 2O to 25 cmH 2O for 8 s (SIGH). We enrolled 24 patients with h-ARF (12 B L and 12 U L) who underwent four consecutive trials: (1) 30 min breathing through a Venturi mask (V MASK), (2) 1 h n-CPAP (n-CPAP 1), (3) 1 h n-CPAP plus SIGH (n-CPAP SIGH), and (4) 1 h n-CPAP (n-CPAP 2). Results: Compared to V MASK, n-CPAP at 10 cmH 2O delivered via a helmet, increased PaO 2/FiO 2 and decreased dyspnea in both B L and U L; furthermore, it reduced the respiratory rate and brought PaCO 2 up to normal in B L only. Compared to n-CPAP, n-CPAP SIGH significantly improved PaO 2/FiO 2 in B L (225 ± 88 vs. 308 ± 105, respectively), whereas it produced no further improvement in PaO 2/FiO 2 in U L (232 ± 72 vs. 231 ± 77, respectively). SIGH did not affect hemodynamics in both groups. Conclusions: Compared to n-CPAP, n-CPAP SIGH further improved arterial oxygenation in B L patients, whereas it produced no additional benefit in those with U L.