Partial liquid ventilation-induced mild hypothermia improves the lung function and alleviates the inflammatory response during acute respiratory distress syndrome in canines

Background Acute respiratory distress syndrome (ARDS), which is the severest form of pulmonary injury, is the leading cause of death in critical care. At present, the mortality remains high in ARDS. Partial liquid ventilation (PLV) using perfluorocarbon (PFC) has been proven to improve gas exchange and respiratory dynamics of the lungs during ARDS. However, PLV has not been shown to reduce the mortality of ARDS. Some studies have shown that mild hypothermia therapy can reduce lung injuries in animal models of ARDS by reducing inflammatory cytokine levels in lung tissues. However, hypothermia cannot produce a lung protection effect alone, and it may have a synergistic effect with other protective measures. To explore the possible role of PLV combined with mild hypothermia in the treatment of ARDS, in this study, we used PFC liquid ventilation to induce mild hypothermia in dogs suffering from ARDS and analyzed the effects of PFC liquid ventilation-induced mild hypothermia on the levels of inflammatory factors and lung histopathology in dogs with ARDS. The experimental dogs were randomly divided into conventional mechanical ventilation (CMV), normal temperature PFC liquid ventilation (NPLV), hypothermic PFC liquid ventilation (HPLV), and mechanical ventilation (MV) groups. After induction of ARDS, the CMV group was treated with CMV for respiratory support, the HPLV group was treated with PLV-induced mild hypothermia using 15 degrees C PFC and maintained the rectal temperature at 34-36 degrees C, the NPLV group was treated with PLV using 36 degrees C PFC and maintained the rectal temperature at 36-38 degrees C. The MV group served as the control group. Analyses of the pulmonary pathology, partial pressure of oxygen in the blood, and lung wet-dry weight ratio (W/T) of each dog revealed that PLV-induced mild hypothermia significantly increased the PaO2 values and attenuated lung injury, and there were no adverse effects on hemodynamics. Furthermore, treatment with PLV-induced mild hypothermia significantly increased the expression of the anti-inflammatory factor IL-10 in bronchoalveolar lavage fluid (BALF) and attenuated the expression of interleukin (IL-6) and tumor necrosis factor-alpha (TNF-alpha) in peripheral blood and in lung BALF. Moreover, the results showed that the expression of myeloperoxidase (MPO) and NF-kappa B p65 in lung tissues was significantly decreased by PLV-induced mild hypothermia compared with NPLV and CMV. Our results indicated that PLV combined with mild hypothermia can provide protection against oleic acid-induced ARDS in dogs.