Recruitment maneuver in experimental acute lung injury: the role of alveolar collapse and edema.
OBJECTIVE
In acute lung injury, recruitment maneuvers have been used to open collapsed lungs and set positive end-expiratory pressure, but their effectiveness may depend on the degree of lung injury. This study uses a single experimental model with different degrees of lung injury and tests the hypothesis that recruitment maneuvers may have beneficial or deleterious effects depending on the severity of acute lung injury. We speculated that recruitment maneuvers may worsen lung mechanical stress in the presence of alveolar edema.


METHODS
Prospective, randomized, controlled experimental study.


METHODS
University research laboratory.


METHODS
Thirty-six Wistar rats randomly divided into three groups (n = 12 per group).


METHODS
In the control group, saline was intraperitoneally injected, whereas moderate and severe acute lung injury animals received paraquat intraperitoneally (20 mg/kg [moderate acute lung injury] and 25 mg/kg [severe acute lung injury]). After 24 hrs, animals were further randomized into subgroups (n = 6/each) to be recruited (recruitment maneuvers: 40 cm H₂O continuous positive airway pressure for 40 secs) or not, followed by 1 hr of protective mechanical ventilation (tidal volume, 6 mL/kg; positive end-expiratory pressure, 5 cm H₂O).


RESULTS
Only severe acute lung injury caused alveolar edema. The amounts of alveolar collapse were similar in the acute lung injury groups. Static lung elastance, viscoelastic pressure, hyperinflation, lung, liver, and kidney cell apoptosis, and type 3 procollagen and interleukin-6 mRNA expressions in lung tissue were more elevated in severe acute lung injury than in moderate acute lung injury. After recruitment maneuvers, static lung elastance, viscoelastic pressure, and alveolar collapse were lower in moderate acute lung injury than in severe acute lung injury. Recruitment maneuvers reduced interleukin-6 expression with a minor detachment of the alveolar capillary membrane in moderate acute lung injury. In severe acute lung injury, recruitment maneuvers were associated with hyperinflation, increased apoptosis of lung and kidney, expression of type 3 procollagen, and worsened alveolar capillary injury.


CONCLUSIONS
In the presence of alveolar edema, regional mechanical heterogeneities, and hyperinflation, recruitment maneuvers promoted a modest but consistent increase in inflammatory and fibrogenic response, which may have worsened lung function and potentiated alveolar and renal epithelial injury.
Santiago
Viviane R
VR
Laboratory of Pulmonary Investigation, Carlos Chagas Filho Institute of Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Rzezinski
Andréia F
AF
Nardelli
Liliane M
LM
Silva
Johnatas D
JD
Garcia
Cristiane S N B
CS
Maron-Gutierrez
Tatiana
T
Ornellas
Debora S
DS
Morales
Marcelo M
MM
Capelozzi
Vera L
VL
Marini
John
J
Pelosi
Paolo
P
Rocco
Patricia R M
PR
D055371:Acute Lung Injury / Q000150:complications / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D000818:Animals; D024061:Collagen Type III / Q000096:biosynthesis; D045422:Continuous Positive Airway Pressure; D015850:Interleukin-6 / Q000096:biosynthesis; D007668:Kidney / Q000473:pathology; D008099:Liver / Q000473:pathology; D008168:Lung / Q000473:pathology; D046529:Microscopy, Electron, Transmission; D011650:Pulmonary Alveoli / Q000293:injuries / Q000473:pathology / Q000503:physiopathology; D001261:Pulmonary Atelectasis / Q000209:etiology* / Q000628:therapy; D011654:Pulmonary Edema / Q000209:etiology* / Q000628:therapy; D051381:Rats; D017208:Rats, Wistar; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology
D024061:Collagen Type III; D015850:Interleukin-6