Hypothermia improves oral and gastric mucosal oxygenation during hypoxic challenges

Abstract

Background. Therapeutic hypothermia, used primarily for protective effects after hypoxia, improves oral and gastric mucosal microvascular oxygenation (μHbO2) during additional haemorrhage. Therefore, we questioned whether hypothermia likewise improves μHbO2 during hypoxic challenges. Since both hypothermia and hypoxia reduce cardiac output (e.g. by myofilament Ca2+ desensitization), and modulate vasomotor tone via K+ATP channels, we hypothesized that the Ca2+ sensitizer levosimendan and K+ATP channel blocker glibenclamide would support the cardiovascular system. Methods. The effects of mild hypothermia (34°C) on μHbO2 during hypoxia (F IO2=0.12, 15 min) were analysed in a cross-over study on five anaesthetized dogs and compared with normothermia (37.5°C) and hypoxia. During hypothermia, but before hypoxia, glibenclamide (0.2 mg kg-1) or levosimendan (20 μg kg-1+0.25 μg kg-1 min -1) was administered. Systemic haemodynamic variables, gastric and oral mucosal microvascular oxygenation (reflectance spectrophotometry), and perfusion (laser Doppler flowmetry) were recorded continuously. Data are presented as mean (SEM), P<0.05. Results. Hypoxia during normothermia reduced gastric μHbO2 by 27 (3)% and oral μHbO2 by 28 (3)% (absolute change). During hypothermia, this reduction was attenuated to 16 (3)% and 13 (1)% (absolute change). This effect was independent of microvascular flow that did not change during hypoxia and hypothermia. Additional administration of levosimendan during hypothermia restored reduced cardiac output but did not change flow or μHbO2 compared with hypothermia alone. Glibenclamide did not exert any additional effects during hypothermia. Conclusions. Hypothermia attenuates the decrease in μHbO2 during additional hypoxic challenges independent of systemic or regional flow changes. A reduction in cardiac output during hypothermia is prevented by Ca2+ sensitization with levosimendan but not by K+ATP channel blockade with glibenclamide. © The Author [2014].