Pulmonary Disease - Volume 15, Part 3, December 2014

highly selected population. In this cohort, a Simplified Acute Physiology Score II (SAPS II) greater than 34 and inability to improve the PaO2/FIO2 ratio after 1 hour predicted failure of noninvasive ventilation. In another study, 38 (70%) of 54 patients with ARDS (including all 19 patients with shock) initially managed with noninvasive ventilation eventually required intubation. 22 Patients who failed noninvasive ventilation also had higher than predicted mortality (68% versus 39%, P < 0.01).

Noninvasive ventilation has not been adequately evaluated in clinical trials to recommend its routine use in patients with ARDS. However, if used it should likely be reserved for patients without shock and with less severe lung injury. Patients should be reassessed within 1 hour and patients without significant physiologic improvement should probably be intubated to avoid potential negative consequences of delayed intubation.

PRONE POSITIONING

Previous studies in adults and children have
shown that while prone positioning transiently
improved oxygenation and lung compliance, it did
not improve outcomes.23–25 Additionally, in a multi-
center randomized clinical trial of 791 patients, the
rates of pressure sores, mainstem endotracheal
intubation, and endotracheal tube obstruction were
increased.24 However, a post-hoc analysis sug-
gested a benefit of proning in patients with more
severe hypoxemia and new technology in rotating
beds (potentially allowing increased frequency of
rotation with reduced nursing time and compli-
cation rates) supported a follow-up trial (Prone-
Supine II).26 Again, despite improved oxygenation
there was no difference in mortality among 342 pa-
tients with moderate and severe ARDS randomly
assigned to prone versus supine positioning. Also,
complications (need for sedation and paralysis,
hemodynamic instability, and device displace-
ment) were higher in the prone group. However,
the 33% 28-day mortality in the supine group was
lower than anticipated, and there was a nonsignifi-
cant 10% difference (53% versus 63%, P = 0.19)
in 6-month mortality among patients with severe
(PaO2/FIO2 <100 mm Hg) ARDS.
A subsequent meta-analysis of 1867 patients
found prone positioning reduced mortality among
555 patients with severe ARDS (relative risk 0.84,
95% confidence interval [CI] 0.74 to 0.96) but not
among patients with moderate ARDS.27 The ben-
efit of prone positioning extended to patients with
a PaO2/FIO2 up to 140 mm Hg. A recent multicenter
trial randomly assigned 466 patients with severe
ARDS (PaO2/FIO2 <150 mm Hg on a FIO2 ≥0.6) to at
least 16 hours a day in the prone position versus
24 hours supine.28 The original ARDS Network low
PEEP protocol was used in both groups. Proning
was performed using standard beds and at least
3 trained staff members to ensure device security
(the online publication in the New England Journal
of Medicine includes an instructional video). Mor-
tality was significantly reduced in the prone group
(16% versus 33%, P < 0.001), with no observed
increase in complications. After adjustment for
the Sequential Organ Failure Assessment (SOFA)
score and use of vasopressors and neuromuscular
blockade, prone positioning was associated with
a 53% reduction in the hazard for death. Impor-
tantly, the theoretical benefit of proning results
from improved recruitment of posterior-basilar lung
units and has not been directly compared to other
recruitment strategies such as high PEEP.