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 Ca(2+) desensitization), and modulate vasomotor tone via K(+) ATP channels, we hypothesized that the Ca(2+) 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 [Formula see text] 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 Ca(2+) sensitization with levosimendan but not by K(+) ATP channel blockade with glibenclamide.