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

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. To perform a recruitment maneuver, once a minute we increased the pressure applied to the airway from 10 cmH(2)O to 25 cmH(2)O 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)). Compared to V(MASK), n-CPAP at 10 cmH(2)O 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 +/- A 88 vs. 308 +/- A 105, respectively), whereas it produced no further improvement in PaO(2)/FiO(2) in U(L) (232 +/- A 72 vs. 231 +/- A 77, respectively). SIGH did not affect hemodynamics in both groups. 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).