Objective To observe the effects of different hypothermia on cerebral oxygen metabolism during cardiopulmonary bypass(CPB).Methods 20 patients undergoing valvular replacements were randomly divided in two groups:shallow hypothermia group(30℃) and middle hypothermia group(26℃).Blood gas analysis and lactate concentration in arterial and internal jugular vein blood were monitored at 3 time points during operation,from which the arterial-internal jugular venous oxygen content difference(Ca-jvO 2),cerebral oxygen extraction ratio(ERO 2),cerebral lactate production(ADVL) were calculated.Results CaO 2,Ca-jvO 2 and ERO 2 of the two groups were significantly reduced(P0 05) at the same time points.Ca-jvO 2 at the T 3 time point was both lower(P