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.