Different strategies to keep the lung open: a study in isolated perfused rabbit lungs.
OBJECTIVE
Atelectatic alveoli can be recruited or kept open either by sustained inflation maneuvers or by positive end-expiratory pressure (PEEP). Little is known about potential interactions between both approaches. Especially, it is not known whether the recruiting effect of sustained inflation maneuvers is maintained in combination with a low PEEP, as suggested recently. In an attempt to answer this question, we combined sustained inflation maneuvers with either high or low PEEP. Both approaches were compared with a strategy likely to result in alveolar atelectasis and with another ensuring adequate alveolar recruitment by adjustment of PEEP alone.


METHODS
Randomized block design.


METHODS
Laboratory.


METHODS
Isolated perfused rabbit lungs (n = 28).


METHODS
The lungs were ventilated with a tidal volume of 8 mL/kg. After stabilization, the lungs were randomized to one of four ventilatory strategies, which then were followed for 120 mins: a) PEEP 1 cm H2O (PEEP1, negative control); b) PEEP 1 cm H2O and 30 sec-sustained inflations (20 cm H2O) every 30 mins (SI-1); c) PEEP 3 cm H2O combined with sustained inflations (SI-3); and d) PEEP repeatedly adjusted following a previously established strategy ensuring full alveolar recruitment (DYN, positive control).


RESULTS
Distribution of ventilation and perfusion (Va/Q distribution) was analyzed by the multiple inert gas elimination technique. Volume-dependent compliance within the tidal volume was determined by using the slice method. Shunt and Va/Q mismatch significantly differed between SI-1 and SI-3, indicating full alveolar recruitment only in the latter. Data of SI-1 did not differ substantially from those of PEEP1, and data obtained in SI-3 were similar to those of DYN.


CONCLUSIONS
First, enduring alveolar recruitment by sustained inflation maneuvers is only possible when the alveoli are stabilized thereafter by sufficient PEEP. Second, a ventilation strategy that uses repeated sustained inflations on a comparably high PEEP may not be superior to adequate adjustment of PEEP alone.
Mols
Georg
G
Department of Anesthesiology and Critical Care Medicine, University of Freiburg, Germany.
Hermle
Gerd
G
Fries
Gisela
G
Benzing
Albert
A
Lichtwarck-Aschoff
Michael
M
Geiger
Klaus
K
Guttmann
Josef
J
D000818:Animals; D066298:In Vitro Techniques; D011175:Positive-Pressure Respiration / Q000379:methods*; D011659:Pulmonary Gas Exchange; D011817:Rabbits; D011897:Random Allocation; D015656:Respiratory Mechanics