N Engl J Med. 2006 Apr 27;354(17):1775-86.
Gattinoni L, Caironi P, Cressoni M, Chiumello D, Ranieri VM, Quintel M, Russo S,
Patroniti N, Cornejo R, Bugedo G.
Istituto di Anestesiologia e Rianimazione, Fondazione Istituto di Ricovero e Cura
a Carattere Scientifico, Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena
di Milano, Università degli Studi di Milano, Milan, Italy.
gattinon@policlinico.mi.it
BACKGROUND: In the acute respiratory distress syndrome (ARDS), positive
end-expiratory pressure (PEEP) may decrease ventilator-induced lung injury by
keeping lung regions open that otherwise would be collapsed. Since the effects of
PEEP probably depend on the recruitability of lung tissue, we conducted a study
to examine the relationship between the percentage of potentially recruitable
lung, as indicated by computed tomography (CT), and the clinical and
physiological effects of PEEP. METHODS: Sixty-eight patients with acute lung
injury or ARDS underwent whole-lung CT during breath-holding sessions at airway
pressures of 5, 15, and 45 cm of water. The percentage of potentially recruitable
lung was defined as the proportion of lung tissue in which aeration was restored
at airway pressures between 5 and 45 cm of water. RESULTS: The percentage of
potentially recruitable lung varied widely in the population, accounting for a
mean (+/-SD) of 13+/-11 percent of the lung weight, and was highly correlated
with the percentage of lung tissue in which aeration was maintained after the
application of PEEP (r2=0.72, P<0.001). On average, 24 percent of the lung could
not be recruited. Patients with a higher percentage of potentially recruitable
lung (greater than the median value of 9 percent) had greater total lung weights
(P<0.001), poorer oxygenation (defined as a ratio of partial pressure of arterial
oxygen to fraction of inspired oxygen) (P<0.001) and respiratory-system
compliance (P=0.002), higher levels of dead space (P=0.002), and higher rates of
death (P=0.02) than patients with a lower percentage of potentially recruitable
lung. The combined physiological variables predicted, with a sensitivity of 71
percent and a specificity of 59 percent, whether a patient’s proportion of
potentially recruitable lung was higher or lower than the median. CONCLUSIONS: In
ARDS, the percentage of potentially recruitable lung is extremely variable and is
strongly associated with the response to PEEP. Copyright 2006 Massachusetts
Medical Society.