The role of mild hypothermia in air embolism-induced acute lung injury.

Background: Mild hypothermia has become an important treatment for ischemic brain injury. However, the role of mild hypothermia in air embolism-induced lung injury has not been explored. In this study, we investigated whether treatment with mild hypothermia before and synchronous with air infusion can attenuate acute lung injury induced by air embolism.

Methods: In this rat model study (Sprague-Dawley rats), pulmonary air embolism was induced by venous infusion of air at a rate of 25 microL/min for 40 minutes. Control animals received no air infusion. The rats were randomly assigned to 2 control groups of normothermia (37 degrees C) and mild hypothermia (34 degrees C) and 3 air embolism groups of mild hypothermia induced before air infusion, normothermia with air infusion, and mild hypothermia induced synchronous with air infusion. At the end of the experiment, the variables of lung injury were assessed.

Results: Air infusion elicited a significant increase in lung wet/dry weight ratio and protein, lactate dehydrogenase, and tumor necrosis factor-alpha concentration of the bronchoalveolar lavage fluid. Myeloperoxidase activity, neutrophil infiltration, and interstitial edema in lung tissue were also significantly increased. In addition, nuclear factor-kappaB activity was significantly increased in the lungs. Treatment with mild hypothermia before air infusion reduced increases in these variables, whereas mild hypothermia synchronous with air infusion had no significant effect on them.

Conclusions: Our study suggests that mild hypothermia before air infusion decreases air embolism-induced acute lung injury. The protective mechanism seems to be the inhibition of inflammation.