Mild Hypothermia via External Cooling Improves Lung Function and Alleviates Pulmonary Inflammatory Response and Damage in Two-Hit Rabbit Model of Acute Lung Injury

Abstract

Objectives Targeted temperature management (TTM) with therapeutic hypothermia (TH) has an organ-protective effect by mainly reducing inflammatory response. Here, our objective was to determine, for the first time, whether mild TH with external cooling, a simple and inexpensive method, could be safe or even beneficial in two-hit rabbit model of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Methods Twenty-two New Zealand rabbits (6-month-old) were randomly divided into healthy control (HC) with conventional ventilation, but without injury, model group (ALI), and hypothermia group with external cooling (ALI-HT). After induction of ALI/ARDS through mild lung-lavages followed by non-protective ventilation, mild hypothermia was started in ALI-HT group (body temperature of 33-34 degrees C). All rabbits were conventionally ventilated for an additional 6-h by recording respiratory parameters. Finally, lung histopathology and inflammatory response were evaluated. Results Hypothermia was associated with higher oxygen saturation, resulting in partial improvement in the P/F ratio (PaO2/FiO(2)), oxygenation index, mean airway pressure, and PaCO2, but did not affect lactate levels. The ALI-HT group had lower histopathological injury scores (hyperemia, edema, emphysema, atelectasis, and PMN infiltration). Further, tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and -8 levels in lung tissue and serum samples markedly reduced due to hypothermia. Conclusion Mild TH with external cooling reduced lung inflammation and damage, whereas it resulted in partial improvement in gas exchanges. Our findings highlight that body temperature control may be a potentially supportive therapeutic option for regulating cytokine production and respiratory parameters in ALI/ARDS.