Effects of hypothermia and CO2 on hypoxic brain injury

CHI Yang; SUN Qian; XIAO Yu-wei; ZHAO Shuang; LU Na; ZHANG He

doi:10.16048/j.issn.2095-5561.2025.03.11

Abstract：Objective To investigate the effects of low temperature and CO2 levels on hypoxic brain injury and provide reference for the detection indicators of hypoxic brain injury animal models.Methods A total of 30 male Bama pigs with a body weight of(15.0±0.3)kg were selected and randomly divided into the hypoxia-normal temperature group,hypoxia-subhypothermia group,hypoxia-hypothermia group,asphyxia-normal temperature group,asphyxia-subhypothermia group,and asphyxia-hypothermia group by random number table method,with 5 pigs in each group.The anorectal temperature of the hypoxia-normal temperature group and the asphyxia-normal temperature group was maintained within the physiological range[(38.5±0.5)℃]using a servo heating pad.The temperature of the hypoxia-subhypothermia group and the asphyxia-subhypothermia group was maintained at(33.5±0.5)℃,and that of the hypoxia-hypothermia group and the asphyxia-hypothermia group was maintained at(28.5±0.5)℃ by controlling the temperature in the high-low temperature environmental simulation training chamber.Hypoxic condition was maintained by ventilation with a hypoxic mixture of 6％O2+94％N2 for 20 minutes,while asphyxia condition was maintained by ventilation with a hypoxic and hypercapnic gas mixture of 6％O2+20％CO2+74％N2 for 20 minutes,and the respiratory rate was reduced from 30 times/min to 15 times/min.Then,all six groups were given 21％O2+79％N2 mechanical ventilation for 60 minutes.Before hypoxia or asphyxia,20 minutes after hypoxia or asphyxia(at the end of 20 minutes of hypoxia or asphyxia),and 60 minutes after resuming oxygen supply,arterial blood samples were collected.The arterial pH,partial pressure of oxygen,partial pressure of carbon dioxide,central blood oxygen saturation,blood glucose,base excess,and lactic acid levels in the blood samples were analyzed using the blood analysis system.The brain interstitial pH was detected using the brain stereotaxic device,and the electrical signal datas of the brain interstitial pH were recorded and saved using the micro-sensor multimeter and sensor tracking and recording software for analysis.Results After 20 min of hypoxia or asphyxia,the blood oxygen saturation and partial pressure of oxygen decreased in the 6 groups,while the partial pressure of carbon dioxide and blood sugar increased,and the partial pressure of carbon dioxide increased more significantly under the induction of asphyxia conditions.At 60 minutes after resuming oxygen supply,the blood oxygen saturation,oxygen partial pressure,carbon dioxide partial pressure and blood sugar in the 6 groups basically recovered to the level before hypoxia or asphyxia.After 20 min of hypoxia or asphyxia,brain interstitial pH and arterial pH decreased.At 20 minutes after induction of hypoxia or asphyxia,the arterial pH of the hypoxia-normal temperature group was higher than that of the asphyxia-normal temperature group,the arterial pH of the asphyxia-normal temperature group was higher than that of the asphyxia-subhypothermia group,the arterial pH of the hypoxia-subhypothermia group was higher than that of the asphyxia-subhypothermia group,and the differences were statistically significant(P＜0.05).At 20 minutes after hypoxia or asphyxia induction,the brain interstitial pH in the hypoxia-normal temperature group was higher than that in the asphyxia-normal temperature group,while the brain interstitial pH in the hypoxia-hypothermia group was lower than that in the hypoxia-normal temperature group,and the differences were statistically significant(P＜0.05).Before hypoxia or asphyxia,the levels of blood base excess and lactic acid in the 6 groups were all within the normal physiological range.At 20 minutes after hypoxia or asphyxia induction,the blood base excess decreased and lactic acid increased.At 60 min after resuming oxygen supply,the level of blood base excess and lactic acid returned to the level before hypoxia or asphyxia induction.At 20 minutes after hypoxia or asphyxia induction,the base excess in the asphyxia-hypothermia group was lower than in the asphyxia-normal temperature group,while the lactic acid level in the asphyxia-hypothermia group was higher than that in the asphyxia-normal temperature group,and the differences were statistically significant(P＜0.05).At 60 minutes after resuming oxygen supply,the lactic acid level in the asphyxia-hypothermia group was higher than that in the asphyxia-normal temperature group,and the lactic acid level in the asphyxia-subhypothermia group was higher than that in the hypoxia-subhypothermia group,and the differences were statistically significant(P＜0.05).Conclusion In the hypoxia model and the asphyxia model,under the condition of low temperature,the extent of cerebral acidosis was similar,while it is mitigated under the sub-hypothermic condition.Brain interstitial pH,blood base excess and lactic acid level can be used as indicators of brain hypoxic model.